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Chronic Lymphocytic Leukemia (CLL)

Definition

• Harrison's Principles of Internal Medicine 22E, p. 893
• Goldman-Cecil Medicine, p. 1928

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Epidemiology

• Most common leukemia in the Western Hemisphere (~20,000+ new US cases/year)
• Median age at diagnosis: 70-72 years
• Male:Female ratio = 2:1 (becomes more equal after age 80)
• More common in Caucasians; rare in Asians/Pacific Islanders even after migration
• 5-year survival improved from 70% (1980) to 92% (2015) and continues to rise
• Strong familial risk: first-degree relatives have 5-8x increased risk; two affected first-degree relatives confer ~27x increased risk
• Associated with Agent Orange/burn pit exposure (service-connected illness for Vietnam veterans)
• NOT linked to radiation exposure (unlike most other leukemias)

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Precursor: Monoclonal B-Cell Lymphocytosis (MBL)

• Low-count MBL (<0.5 × 10⁹/L): negligible risk of progression
• High-count MBL (0.5-5 × 10⁹/L): progresses to CLL at 1-2% per year
• MBL prevalence is ~12% in general population, ~18% in first-degree relatives of CLL patients

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Pathology & Immunophenotype

• Henry's Clinical Diagnosis and Management by Laboratory Methods, p. 3954

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Cytogenetics and Molecular Prognostic Markers

• Unmutated IGHV (immunoglobulin heavy-chain variable region) - in ~50% of cases; associated with ZAP-70 expression, CD38 expression, and worse prognosis
• TP53 mutation/del(17p): resistance to chemoimmunotherapy
• NOTCH1, SF3B1, BIRC3 mutations: additional adverse features
• β₂-microglobulin elevation, lymphocyte doubling time <12 months: adverse

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Staging

• Washington Manual of Medical Therapeutics, p. 867

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Clinical Presentation

• Most patients are asymptomatic at diagnosis, found incidentally on CBC
• When symptomatic: fatigue, weight loss, night sweats, lymphadenopathy
• Infections (leading cause of morbidity/mortality; 30-50% of deaths)
• Autoimmune complications: Autoimmune hemolytic anemia (AIHA), immune thrombocytopenia (ITP)
• Richter transformation: CLL transforms to diffuse large B-cell lymphoma (DLBCL) in ~5% - presents with rapid nodal enlargement, B symptoms, elevated LDH

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Treatment Indications

• Progressive marrow failure (worsening anemia/thrombocytopenia)
• Massive or symptomatic splenomegaly (>6 cm below costal margin)
• Lymphadenopathy >10 cm in longest diameter
• Progressive lymphocytosis (>50% increase in 2 months or doubling time <6 months)
• Symptomatic disease (significant fatigue, night sweats, weight loss, fever)
• AIHA or ITP poorly responsive to steroids

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Treatment

• Ibrutinib - first-generation; once daily; continuous therapy
• Acalabrutinib - more selective, fewer off-target effects (preferred over ibrutinib for cardiac patients)
• Zanubrutinib - most selective BTK inhibitor; shown superior to ibrutinib in relapsed CLL

• Venetoclax - used in combination with obinutuzumab (anti-CD20) as fixed-duration therapy; also with ibrutinib or rituximab

• FCR (fludarabine, cyclophosphamide, rituximab) - still used for young, fit patients with mutated IGHV (potential for very long-term remission)

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Key Complications Summary

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• Harrison's Principles of Internal Medicine 22E (2025), Ch. 112
• Goldman-Cecil Medicine International Edition, Ch. on CLL
• Washington Manual of Medical Therapeutics, p. 867
• Henry's Clinical Diagnosis and Management by Laboratory Methods, p. 3954

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Chronic Myeloid Leukemia (CML)

Definition

• Goldman-Cecil Medicine, p. 1938
• Robbins Pathologic Basis of Disease

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Pathogenesis

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Epidemiology

• Accounts for ~14-15% of all leukemias
• Annual incidence: ~2 per 100,000; ~8,000-9,000 new US cases/year
• Median age at diagnosis: 55-65 years (younger than CLL)
• Slight male predominance (M:F = 1.6:1)
• Uncommon in children (<3% of CML cases under age 20)
• Risk factors: ionizing radiation (unlike CLL); no consistent links to chemical exposures

• Pre-TKI era: median survival 3-7 years; 10-year survival <30%
• TKI era (imatinib): 10-year survival >85%, approaching age-matched normal population

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Clinical Phases

1. Chronic Phase (~75% at diagnosis)

• Insidious onset; most patients found incidentally on routine CBC
• Symptoms when present: fatigue, weight loss, anorexia, splenomegaly (left upper quadrant dragging pain, early satiety, splenic infarction)
• Peripheral blood: marked leukocytosis (often >100,000 cells/µL) with the full granulocytic spectrum - neutrophils, band forms, metamyelocytes, myelocytes, eosinophils, basophilia (characteristic)
• Blasts typically <10% in blood
• Platelets often elevated (sometimes markedly)
• Bone marrow: markedly hypercellular, granulocytic hyperplasia, "sea-blue histiocytes" (scattered macrophages with green-blue cytoplasm), increased reticulin

2. Accelerated Phase

• Worsening anemia and thrombocytopenia, rising basophils
• Additional clonal cytogenetic abnormalities (trisomy 8, isochromosome 17q, duplication of Ph chromosome)
• ELN criteria: blasts 15-<30% in blood or marrow
• WHO criteria: blasts 10-20%

3. Blast Phase (Blast Crisis)

• Resembles acute leukemia
• ELN criteria: blasts ≥30%; WHO criteria: blasts ≥20%
• 70% myeloid blast crisis, ~30% lymphoid blast crisis (pre-B cell) - evidence that CML originates from a pluripotent stem cell
• Prognosis poor; modest benefit from TKIs in blast phase

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Diagnosis

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Staging / Response Criteria

• By 3 months: BCR-ABL1 ≤10% (IS)
• By 6 months: BCR-ABL1 ≤1% (IS) / CCyR
• By 12 months: BCR-ABL1 ≤0.1% (IS) = MMR

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TKI Therapy - The Cornerstone of Treatment

• Nilotinib is 30x more potent than imatinib (structurally similar)
• Dasatinib is ~300x more potent; also inhibits SRC kinases
• Bosutinib is 30-50x more potent; also inhibits SRC kinases
• Ponatinib and asciminib are active against the T315I "gatekeeper" mutation (resistant to all other TKIs)
• Asciminib is a STAMP inhibitor - uniquely targets the ABL myristoyl pocket (allosteric inhibition) rather than the ATP binding site - a different mechanism from all other TKIs
• Asciminib in newly diagnosed CML (ASCEMBL trial data, NEJM 2024) shows promising results as 1st-line therapy

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TKI Resistance and Mutations

• Most common resistance mutations: E255K, Y253H (nilotinib/dasatinib sensitive mutations)
• T315I ("gatekeeper mutation"): confers resistance to all 1st and 2nd generation TKIs → use ponatinib or asciminib

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Treatment-Free Remission (TFR)

• ~40-60% of eligible patients maintain TFR
• Most relapses occur within the first 6 months and respond to TKI rechallenge
• Requires close molecular monitoring after stopping

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Management of Advanced Phase / Blast Crisis

• Accelerated phase: TKIs (often higher dose or 2nd/3rd generation) ± consideration of allogeneic HSCT
• Blast crisis: TKI + acute leukemia-type chemotherapy (regimen depends on myeloid vs. lymphoid crisis) → bridge to allogeneic HSCT if response achieved
• HSCT is now a later-line option after TKI failure; no longer first-line for chronic phase

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CML vs. Leukemoid Reaction (key differential)

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• Harrison's Principles of Internal Medicine 22E (2025), Ch. 110
• Goldman-Cecil Medicine International Edition, Ch. on CML
• Robbins Pathologic Basis of Disease, Ch. 13
• Washington Manual of Medical Therapeutics, p. 866

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Chronic Myeloid Leukemia (CML)

Definition

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Pathogenesis

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Epidemiology

• ~14-15% of all leukemias; ~8,000-9,000 new US cases/year
• Median age: 55-65 years; male predominance (M:F = 1.6:1)
• Risk factor: ionizing radiation (unlike CLL)
• Pre-TKI: median survival 3-7 years | TKI era: 10-year survival >85%

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Clinical Phases

1. Chronic Phase (~75% at diagnosis)

• Usually asymptomatic, found on routine CBC
• Symptoms: fatigue, weight loss, splenomegaly (LUQ pain, early satiety)
• Blood: leukocytosis often >100,000/µL, full granulocytic spectrum, basophilia (characteristic), eosinophilia, thrombocytosis
• Blasts <10%; bone marrow hypercellular with "sea-blue histiocytes"

2. Accelerated Phase

• Worsening anemia/thrombocytopenia, rising basophils
• Additional cytogenetic abnormalities (trisomy 8, iso17q, Ph duplication)
• ELN: blasts 15-<30% | WHO: blasts 10-20%

3. Blast Phase (Blast Crisis)

• Resembles acute leukemia
• ELN: blasts ≥30% | WHO: blasts ≥20%
• 70% myeloid, ~30% lymphoid (pre-B cell) - confirms pluripotent stem cell origin
• 50% progress through accelerated phase; 50% go directly to blast crisis

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Diagnosis

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Treatment Response Milestones

• CHR: normalized CBC + no splenomegaly
• CCyR: no Ph+ metaphases on marrow cytogenetics
• MMR (MR3): BCR-ABL1 ≤0.1% IS
• Deep MR (MR4/MR4.5): ≤0.01% / ≤0.0032% IS - required for TFR attempt

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FDA-Approved TKIs

• Nilotinib = 30x more potent than imatinib
• Dasatinib = ~300x more potent; also inhibits SRC kinases
• Ponatinib + Asciminib = active against T315I "gatekeeper" mutation
• Asciminib uniquely targets the ABL myristoyl pocket (allosteric) - different from all other TKIs
• First-line choice guided by comorbidities, toxicity profile, and TFR goal

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TKI Resistance

• Test for BCR-ABL1 kinase domain mutations when milestones not met
• T315I mutation → resistant to all 1st/2nd gen TKIs → use ponatinib or asciminib
• Omacetaxine (protein synthesis inhibitor): option when TKI resistance is BCR-ABL mutation-independent

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Treatment-Free Remission (TFR)

• Patients achieving sustained MR4.5 may attempt TKI discontinuation
• ~40-60% maintain TFR; most relapses within 6 months and respond to TKI rechallenge
• Requires close molecular monitoring

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Advanced Phase Management

• Accelerated phase: 2nd/3rd gen TKI ± allogeneic HSCT consideration
• Blast crisis: TKI + acute leukemia chemotherapy (myeloid vs. lymphoid regimen) → bridge to allogeneic HSCT
• HSCT is now later-line (after TKI failure), not first-line for chronic phase

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CML vs. Leukemoid Reaction

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30 Clinical Vignettes: Myeloproliferative Neoplasms

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SECTION 1: CHRONIC MYELOID LEUKEMIA (CML)

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Vignette 1 - CML Diagnosis

• A) Acute myeloid leukemia
• B) Chronic myeloid leukemia
• C) Leukemoid reaction
• D) Primary myelofibrosis
• E) Chronic myelomonocytic leukemia

• ✅ B is correct. The classic triad of CML: massive splenomegaly + extreme leukocytosis with the full granulocytic spectrum (not just blasts) + low LAP score. Basophilia is a hallmark. The WBC is predominantly mature and maturing forms; blasts <10% is consistent with chronic phase.
• ❌ A (AML): AML presents with a high blast percentage (≥20%), not the mature left shift spectrum seen here. Also, cytopenias are more prominent in AML.
• ❌ C (Leukemoid reaction): Leukemoid reactions have a high LAP score (>100), occur in response to infection/inflammation, and lack basophilia or the full granulocytic spectrum at this magnitude.
• ❌ D (PMF): PMF has splenomegaly and leukoerythroblastosis but WBC is rarely >50,000, and teardrop cells (dacryocytes) dominate. Marrow fibrosis is key.
• ❌ E (CMML): CMML is defined by persistent monocytosis >1 × 10⁹/L, not the picture described here.

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Vignette 2 - CML Confirmatory Test

• A) JAK2 V617F mutation PCR
• B) BCR-ABL1 by RT-PCR (quantitative PCR)
• C) FISH for del(13q)
• D) FLT3-ITD mutation
• E) CALR exon 9 mutation

• ✅ B is correct. BCR-ABL1 qPCR on the International Scale (IS) is the gold standard for both confirming CML and monitoring treatment response. It detects the chimeric BCR::ABL1 mRNA transcript.
• ❌ A (JAK2 V617F): This is the mutation in PV, ET, and PMF - not CML.
• ❌ C (FISH del(13q)): This is an adverse prognostic marker in CLL, not relevant here.
• ❌ D (FLT3-ITD): This mutation is associated with AML, particularly AML-M3/M5.
• ❌ E (CALR): CALR mutations are found in JAK2-negative ET and PMF, not CML.

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Vignette 3 - CML Treatment Response Monitoring

• A) Treatment failure
• B) Suboptimal response
• C) Optimal response - Major Molecular Response achieved
• D) Complete cytogenetic response only
• E) Treatment-free remission

• ✅ C is correct. MMR = BCR-ABL1 ≤0.1% IS (a 3-log reduction). Her 12-month level of 0.08% achieves this milestone. ELN milestones: ≤10% at 3 months, ≤1% at 6 months, ≤0.1% at 12 months. All three are met - this is optimal response.
• ❌ A (Failure): Failure at 12 months = BCR-ABL1 >1% IS or new mutations. Her result is far below this.
• ❌ B (Suboptimal): Suboptimal would be intermediate levels, e.g., BCR-ABL1 between 0.1% and 1% at 12 months.
• ❌ D: CCyR (no Ph+ metaphases) is a cytogenetic assessment. MMR by qPCR is the more sensitive and standard monitoring tool today.
• ❌ E (TFR): Treatment-free remission requires sustained deep molecular response (MR4.5) for ≥2 years before attempting TKI discontinuation. This is month 12 only.

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Vignette 4 - CML Resistance Mutation

• A) Switch to nilotinib
• B) Switch to bosutinib
• C) Switch to ponatinib or asciminib
• D) Add hydroxyurea and continue dasatinib
• E) Proceed immediately to allogeneic HSCT

• ✅ C is correct. The T315I mutation (substitution of isoleucine for threonine at position 315 in the ABL kinase domain) is called the "gatekeeper mutation" because it abolishes hydrogen bonding with ALL 1st and 2nd generation TKIs (imatinib, dasatinib, nilotinib, bosutinib). Only ponatinib (3rd gen) and asciminib (STAMP inhibitor, targets the myristoyl pocket) are active against T315I.
• ❌ A (Nilotinib): T315I confers resistance to nilotinib. Switching to another 2nd gen TKI is futile.
• ❌ B (Bosutinib): Same reason - T315I is resistant to bosutinib.
• ❌ D: Adding hydroxyurea is a temporizing measure (cytoreduction) but does not overcome kinase domain resistance.
• ❌ E (HSCT): HSCT may ultimately be needed if TKI options fail, but a targeted switch to an active agent is always tried first.

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Vignette 5 - CML Blast Crisis

• A) Accelerated phase CML; switch to 2nd gen TKI
• B) Myeloid blast crisis of CML; TKI + AML-type induction chemotherapy, then allogeneic HSCT if response
• C) Lymphoid blast crisis of CML; TKI + ALL-type chemotherapy
• D) De novo AML; standard 7+3 chemotherapy alone
• E) Myeloid blast crisis; hydroxyurea cytoreduction only

• ✅ B is correct. Blast crisis = blasts ≥30% (ELN) or ≥20% (WHO) in a patient with known CML. Myeloid markers (MPO+, CD33+) confirm myeloid blast crisis, which accounts for ~70% of blast crises. Management: continue or add a TKI (to suppress BCR-ABL) PLUS AML-type induction chemotherapy to achieve remission, followed by allogeneic HSCT as the only potentially curative approach.
• ❌ A: Blasts of 38% are above the accelerated phase threshold (15-30% by ELN). This is blast crisis, not accelerated phase.
• ❌ C: The blasts are MPO+ and CD33+, confirming myeloid lineage. Lymphoid blast crisis would be TdT+, CD19+, CD10+, requiring ALL-type chemotherapy (e.g., with hyper-CVAD).
• ❌ D: This is not de novo AML - the history of CML on imatinib + known BCR-ABL positivity makes this CML blast crisis. Management differs because a TKI must be part of the regimen.
• ❌ E: Hydroxyurea alone is purely palliative and does not alter disease course in blast crisis.

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Vignette 6 - Asciminib Mechanism

• A) Inhibits the ATP-binding site of BCR-ABL
• B) Inhibits SRC kinase family in addition to ABL
• C) Targets the ABL myristoyl pocket (allosteric inhibition) - a STAMP inhibitor
• D) Inhibits JAK2 signaling downstream
• E) Promotes apoptosis via BCL-2 inhibition

• ✅ C is correct. Asciminib is a STAMP (Specifically Targeting the ABL Myristoyl Pocket) inhibitor. It binds the myristoyl pocket at the C-terminal end of the ABL kinase - an allosteric site completely different from the ATP-binding cleft. This means it works even when ATP-site mutations confer resistance to other TKIs, and it can be combined with ATP-competitive TKIs for additive/synergistic effects.
• ❌ A: All other TKIs (imatinib, dasatinib, nilotinib, bosutinib, ponatinib) work by blocking the ATP-binding site of BCR-ABL.
• ❌ B: SRC kinase inhibition is a feature of dasatinib and bosutinib, not asciminib.
• ❌ D: JAK2 inhibition describes ruxolitinib, used in PV and myelofibrosis.
• ❌ E: BCL-2 inhibition describes venetoclax, used in CLL and AML.

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SECTION 2: POLYCYTHEMIA VERA (PV)

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Vignette 7 - Classic PV Presentation

• A) BCR-ABL1 t(9;22)
• B) CALR exon 9 frameshift
• C) JAK2 V617F (valine-to-phenylalanine at position 617)
• D) MPL W515L
• E) FIP1L1-PDGFRA

• ✅ C is correct. JAK2 V617F is present in 95-98% of PV cases. It causes constitutive activation of the JAK-STAT pathway, making erythroid progenitors growth factor-independent (EPO-independent). The result is panmyeloid proliferation, but red cell excess dominates. The low EPO is the critical distinguishing feature from secondary polycythemia (where EPO is elevated to drive RBC production).
• The clinical picture - aquagenic pruritus (histamine from basophils), plethora, DVT history, hypertension, splenomegaly - is classic PV.
• ❌ A (BCR-ABL1): This is CML. PV does NOT have the Philadelphia chromosome.
• ❌ B (CALR): CALR mutations are found in ~25-35% of ET and PMF cases (JAK2-negative). Not PV.
• ❌ D (MPL W515L): MPL mutations occur in ET (~5-10%) and PMF. Not PV.
• ❌ E (FIP1L1-PDGFRA): This is found in chronic eosinophilic leukemia, not PV.

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Vignette 8 - PV vs Secondary Polycythemia

• A) Hgb level above 18.5 g/dL
• B) Elevated EPO and normal WBC/platelets with a cause of hypoxia
• C) Absence of JAK2 V617F must be confirmed by PCR
• D) Bone marrow biopsy showing no panmyelosis
• E) B, C, and D are all correct

• ✅ E is correct. Distinguishing PV from secondary polycythemia requires multiple criteria:
  • In secondary polycythemia (e.g., COPD, high-altitude, EPO-secreting tumors): EPO is elevated (compensatory); only RBCs increase; WBC and platelets are normal; no splenomegaly; no JAK2 mutation.
  • In PV: EPO is low (suppressed by autonomous RBC production); WBC and platelets often elevated (panmyelosis); splenomegaly; JAK2 V617F present; bone marrow shows hypercellularity with panmyelosis.
• The key single discriminator is: low EPO + JAK2 V617F = PV; elevated EPO + hypoxia cause = secondary.

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Vignette 9 - PV Complication: Budd-Chiari

• A) Antiphospholipid syndrome
• B) Polycythemia vera - send JAK2 V617F
• C) Paroxysmal nocturnal hemoglobinuria (PNH)
• D) Factor V Leiden
• E) Essential thrombocythemia

• ✅ B is correct. Budd-Chiari syndrome (hepatic vein thrombosis) is a classic and serious complication of PV, caused by increased blood viscosity and platelet dysfunction leading to thrombosis of unusual sites. PV should be suspected in any patient with abdominal vein thrombosis (hepatic, portal, mesenteric veins). The elevated Hgb (>16.0 g/dL in women), thrombocytosis, and aquagenic pruritus are all pointing to PV. JAK2 V617F must be tested.
• ❌ A: APS can cause thrombosis but does not explain the polycythemia/pruritus.
• ❌ C: PNH causes hemolytic anemia and venous thrombosis but presents with hemoglobinuria and cytopenias, not polycythemia.
• ❌ D: Factor V Leiden causes DVT/PE but not the hematologic picture described.
• ❌ E: ET can also cause hepatic vein thrombosis but would not explain the elevated Hgb.

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Vignette 10 - PV Treatment

• A) Observation only - PV rarely causes mortality
• B) Phlebotomy alone to target Hct <45%, plus low-dose aspirin
• C) Phlebotomy + hydroxyurea (cytoreductive therapy) + low-dose aspirin, given high-risk features
• D) Ruxolitinib alone
• E) Allogeneic HSCT immediately

• ✅ C is correct. This patient is high-risk (age ≥60 AND prior thrombotic event - TIA). High-risk PV requires:
  1. Phlebotomy to target Hct <45% (reduces thrombotic risk)
  2. Cytoreductive therapy - hydroxyurea is first-line for high-risk PV
  3. Low-dose aspirin (81 mg) to reduce microvascular events
• ❌ A: Untreated PV patients die of vascular complications within months. Median survival with treatment is ~10 years.
• ❌ B: Phlebotomy alone is appropriate only for low-risk PV (age <60, no thrombosis history). High-risk patients need cytoreduction.
• ❌ D: Ruxolitinib (JAK1/2 inhibitor) is used for PV refractory to or intolerant of hydroxyurea - it is second-line, not first-line cytoreduction.
• ❌ E: HSCT is not standard for PV; it is considered only for transformation to myelofibrosis or AML.

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Vignette 11 - PV "Spent Phase"

• A) Transformation to AML
• B) Iron deficiency from repeated phlebotomy
• C) Post-PV myelofibrosis (spent phase transformation)
• D) New diagnosis of primary myelofibrosis
• E) CML transformation

• ✅ C is correct. PV can progress to a "spent phase" or post-PV myelofibrosis in ~10-20% of patients, typically after >10 years. The hallmarks are: paradoxical normalization/fall in Hgb (marrow no longer producing effectively), massive splenomegaly (extramedullary hematopoiesis compensating), leukoerythroblastic blood smear (teardrop cells + nucleated RBCs + immature granulocytes), and marrow fibrosis replacing hematopoietic cells.
• ❌ A (AML): AML transformation occurs in ~1-2% of PV cases; presents with high blast count (≥20%).
• ❌ B: Iron deficiency from phlebotomy causes microcytic anemia; it does not cause marrow fibrosis or leukoerythroblastosis.
• ❌ D: This is NOT de novo PMF - she has a documented 12-year history of PV. Post-PV MF is a known complication.
• ❌ E: CML transformation does not occur from PV.

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SECTION 3: ESSENTIAL THROMBOCYTHEMIA (ET)

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Vignette 12 - ET Diagnosis

• A) Start hydroxyurea immediately
• B) Test for CALR exon 9 and MPL W515L mutations
• C) Bone marrow biopsy alone is sufficient
• D) Diagnose reactive thrombocytosis and reassure
• E) Test for BCR-ABL1 to exclude CML

• ✅ B is correct. When JAK2 V617F is negative in a patient with suspected ET or PMF, the next step is to test for CALR (~30% of ET) and MPL (~5-10% of ET) mutations. The clinical picture (thrombocytosis >450,000/µL + erythromelalgia + visual symptoms) is classic ET. JAK2 V617F is positive in only ~50-60% of ET.
• ❌ A: Treatment should not precede diagnosis confirmation.
• ❌ C: Bone marrow biopsy is important for diagnosis but is done alongside - not instead of - molecular testing. The diagnostic criteria require marrow morphology AND mutation status together.
• ❌ D: Reactive thrombocytosis is caused by inflammation, iron deficiency, post-splenectomy, or infection. Normal CRP and iron, plus giant platelets and erythromelalgia, make clonal ET far more likely.
• ❌ E: BCR-ABL1 must be excluded, but the absence of leukocytosis, left shift, basophilia, and splenomegaly makes CML very unlikely. Still, it is part of the WHO/ICC workup for ET - but CALR/MPL testing is the more targeted next step given JAK2 negativity.

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Vignette 13 - ET and Bleeding

• A) Thrombocytopenia-related bleeding; transfuse platelets
• B) Acquired von Willebrand disease from platelet binding of large VWF multimers; check ristocetin cofactor activity
• C) Hemophilia A; check Factor VIII level
• D) DIC; check fibrinogen and D-dimer
• E) Platelet dysfunction from aspirin; hold aspirin

• ✅ B is correct. When platelet counts exceed ~1,000,000-1,500,000/µL in ET, platelets bind and remove the large von Willebrand factor multimers (the most hemostatically effective) from circulation, causing acquired von Willebrand disease (Type 2A-like). Paradoxically, extreme thrombocytosis INCREASES bleeding risk, not just thrombosis. Preoperatively: check ristocetin cofactor activity (reduced <30% indicates aVWD) and VWF multimer analysis (loss of high-molecular-weight multimers confirms aVWD). Surgery should be deferred until platelets are reduced by cytoreduction.
• ❌ A: Platelets are markedly elevated, not low. Transfusion would worsen the problem.
• ❌ C: Hemophilia A is a congenital clotting factor deficiency, unrelated to ET.
• ❌ D: DIC involves consumption of clotting factors and fibrinogen; the patient has no sepsis, malignancy exacerbation, or trigger for DIC.
• ❌ E: While aspirin affects platelet function, it does not explain aVWD in the context of extreme thrombocytosis.

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Vignette 14 - ET Risk Stratification and Treatment

• A) High-risk: start hydroxyurea immediately
• B) Very high-risk: allogeneic HSCT recommended
• C) Low-risk: observation + low-dose aspirin
• D) Intermediate-risk: interferon-alpha preferred
• E) Low-risk: no treatment, not even aspirin needed

• ✅ C is correct. ET risk stratification:
  • High-risk: Age ≥60 OR prior thrombosis OR platelet count >1,500,000 (bleeding risk)
  • Low-risk: Age <60, no thrombosis, no extreme thrombocytosis
  • This 44-year-old woman has no high-risk features → low-risk ET. Management: observation + low-dose aspirin (reduces microvascular symptoms like erythromelalgia and headaches). The presence of JAK2 mutation confers a modestly higher thrombotic risk, supporting aspirin use.
• ❌ A: Cytoreductive therapy (hydroxyurea) is reserved for high-risk ET patients.
• ❌ B: HSCT is not a standard treatment for ET regardless of risk.
• ❌ D: Interferon-alpha is an alternative cytoreductive option (preferred in young patients wanting pregnancy), but is not indicated in low-risk disease.
• ❌ E: Aspirin is recommended for symptomatic low-risk ET (erythromelalgia, headaches) and in JAK2+ patients.

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Vignette 15 - ET Erythromelalgia

• A) Peripheral neuropathy; gabapentin
• B) Raynaud phenomenon; calcium channel blocker
• C) Erythromelalgia due to platelet microvascular occlusion; low-dose aspirin
• D) Deep vein thrombosis; anticoagulation
• E) Cellulitis; antibiotics

• ✅ C is correct. Erythromelalgia is a microvascular thrombotic syndrome caused by occlusion of small arterioles by platelet aggregates in ET (and PV). It presents with episodic burning pain + redness + warmth of hands/feet, triggered by warmth, and relieved by cold and elevation. It is characteristically and dramatically relieved by low-dose aspirin, which is essentially diagnostic. This distinguishes it from other causes of hand/foot pain.
• ❌ A: Neuropathy presents with numbness/tingling, not burning erythema relieved by cold. Aspirin would not help neuropathy.
• ❌ B: Raynaud phenomenon causes vasoconstriction → pallor → cyanosis → redness (triphasic), triggered by cold, not warmth. Treatment is calcium channel blockers.
• ❌ D: DVT presents with unilateral leg swelling, tenderness, and requires anticoagulation. Erythromelalgia is bilateral and microvascular, not a large-vessel DVT.
• ❌ E: Cellulitis is unilateral, associated with fever, lymphangitis, and leukocytosis; it is not episodic and not platelet-related.

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SECTION 4: PRIMARY MYELOFIBROSIS (PMF)

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Vignette 16 - PMF Classic Presentation

• A) Hypercellular marrow with panmyelosis and no fibrosis
• B) Hypocellular marrow with fat replacement
• C) Clusters of atypical megakaryocytes + reticulin/collagen fibrosis + osteosclerosis
• D) 30% myeloblasts with Auer rods
• E) Dense lymphocytic infiltrate with CD5+ CD23+ B cells

• ✅ C is correct. PMF bone marrow shows the pathognomonic combination of:
  1. Megakaryocytic proliferation and atypia - enlarged, immature megakaryocytes with "cloud-like" nuclei, clustering around sinuses and trabeculae
  2. Reticulin (early) and collagen (late) fibrosis
  3. Osteosclerosis in up to 50% of cases on X-ray The leukoerythroblastic blood smear (teardrop cells + NRBCs + immature WBCs) reflects bone marrow dysfunction and extramedullary hematopoiesis in the spleen/liver.
• ❌ A: Panmyelosis without fibrosis describes PV (early stage).
• ❌ B: Hypocellular marrow with fat replacement describes aplastic anemia.
• ❌ D: ≥20% blasts + Auer rods = AML.
• ❌ E: CD5+/CD23+ B-cell infiltrate is the hallmark of CLL/SLL.

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Vignette 17 - PMF Molecular Markers

• A) FLT3 and NPM1 mutations
• B) CALR exon 9 mutation and MPL W515 mutation
• C) TP53 and RUNX1 mutations
• D) KIT D816V mutation
• E) No further testing is needed; PMF is a clinical diagnosis

• ✅ B is correct. In PMF, if JAK2 V617F is negative, the next step is to test for:
  • CALR (calreticulin) exon 9 frameshift mutations: present in ~25-35% of PMF
  • MPL W515L/K mutations: present in ~5-10% of PMF Together with JAK2, these three cover ~85-90% of PMF cases. A small minority are "triple-negative" (no JAK2/CALR/MPL), which carries the worst prognosis and requires expert bone marrow evaluation.
• ❌ A: FLT3 and NPM1 are AML mutations.
• ❌ C: TP53 and RUNX1 are associated with MDS or AML transformation, not primary PMF diagnosis.
• ❌ D: KIT D816V is the hallmark of systemic mastocytosis.
• ❌ E: Molecular markers are now a required part of WHO/ICC diagnostic criteria for PMF.

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Vignette 18 - PMF Prognostication

• A) Low risk (0 points)
• B) Intermediate-1 risk (1 point)
• C) Intermediate-2 risk (2 points)
• D) High risk (≥3 points)
• E) Cannot be determined without bone marrow blast count

• ✅ D is correct. The IPSS for PMF assigns 1 point each for:
  1. Age >65 ✅ (70 years)
  2. Constitutional symptoms ✅ (night sweats, weight loss)
  3. Hgb <10 g/dL ✅ (9.8 g/dL)
  4. WBC >25,000/µL ✅ (28,000)
  5. Circulating blasts ≥1% ✅ (3%)
  Score = 5 points = High risk (median survival ~27 months). Scores: 0=Low, 1=Int-1, 2=Int-2, ≥3=High. High-risk PMF should be evaluated for allogeneic HSCT (the only potentially curative approach) if the patient is eligible.

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Vignette 19 - PMF Treatment

• A) Imatinib (BCR-ABL TKI)
• B) Hydroxyurea alone
• C) Ruxolitinib (JAK1/2 inhibitor)
• D) Prednisone
• E) Lenalidomide

• ✅ C is correct. Ruxolitinib is a JAK1/2 inhibitor FDA-approved for intermediate-2 and high-risk PMF (and also for PV refractory to hydroxyurea). It significantly reduces spleen size, improves constitutional symptoms (night sweats, fatigue, weight loss), and improves quality of life. The COMFORT-I and COMFORT-II trials demonstrated its superiority over placebo and best available therapy. It is the standard of care for symptomatic PMF in non-transplant candidates.
• ❌ A (Imatinib): CML is BCR-ABL driven. PMF is JAK2/CALR/MPL driven. Imatinib has no role in PMF.
• ❌ B (Hydroxyurea): Hydroxyurea can reduce leukocytosis and mild splenomegaly but is inferior to ruxolitinib for symptom control and spleen reduction in high-risk PMF.
• ❌ D (Prednisone): Steroids may modestly improve anemia in PMF but do not address the core disease process or splenomegaly.
• ❌ E (Lenalidomide): Lenalidomide + prednisone may help anemia in del(5q) MDS or occasionally PMF-related anemia, but is not standard first-line for symptomatic PMF.

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Vignette 20 - PMF Fibrosis on Imaging

• A) Osteoporosis; indicates increased fracture risk
• B) Lytic bone lesions; indicates transformation to AML
• C) Osteosclerosis; reflects extramedullary osteoblastic activity driven by abnormal megakaryocyte cytokines
• D) Paget's disease; an incidental finding
• E) Metastatic bone disease; requires oncology referral

• ✅ C is correct. Osteosclerosis (diffuse increased bone density) is found in up to 50% of PMF patients on radiography. It results from abnormal megakaryocytes releasing fibrogenic and osteogenic cytokines (TGF-β, PDGF, bFGF), which stimulate both reticulin/collagen fibrosis in the marrow AND osteoblastic activity in bone. This is distinct from the lytic lesions of myeloma or metastatic disease.
• ❌ A: Osteoporosis means decreased bone density (radiolucency). PMF causes the opposite.
• ❌ B: Lytic lesions (punched-out) are characteristic of multiple myeloma.
• ❌ D: Paget's disease has a characteristic mosaic/disorganized pattern and elevated alkaline phosphatase; it is a separate diagnosis.
• ❌ E: Metastatic bone disease typically causes lytic or blastic lesions in isolated areas, not the diffuse pattern of PMF-related osteosclerosis.

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SECTION 5: OVERLAP AND DIFFERENTIAL DIAGNOSIS

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Vignette 21 - MPN Differentiation

• A) Patient 1 = CML, Patient 2 = PV
• B) Patient 1 = PV, Patient 2 = CML
• C) Patient 1 = ET, Patient 2 = PMF
• D) Patient 1 = PMF, Patient 2 = ET
• E) Patient 1 = Secondary polycythemia, Patient 2 = CML

• ✅ B is correct.
  • Patient 1 = PV: Elevated Hgb/Hct + panmyeloid proliferation + low EPO (autonomous) + JAK2 V617F + aquagenic pruritus (histamine from basophils) = classic PV.
  • Patient 2 = CML: Extreme leukocytosis with full granulocytic spectrum + basophilia + low LAP (opposite of leukemoid reaction) + BCR-ABL1 fusion = CML.
  • The two key discriminators: EPO (low in PV, normal in CML) and LAP (low in CML, elevated in leukemoid reaction and reactive states).

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Vignette 22 - Philadelphia Chromosome Negative vs Positive

• A) PV, ET, and PMF are Ph-negative MPNs driven by JAK2/CALR/MPL mutations
• B) All MPNs have BCR-ABL1 by PCR even if cytogenetics are normal
• C) CML is Ph-negative in 50% of cases
• D) JAK2 mutations are found in CML but not PV
• E) The Philadelphia chromosome is only found in ALL, not CML

• ✅ A is correct. The WHO/ICC classifies MPNs into Ph-positive (CML) and Ph-negative (PV, ET, PMF). The Ph-negative MPNs are driven by activating mutations in JAK2 (all three), CALR (ET, PMF), and MPL (ET, PMF) - all leading to constitutive JAK-STAT pathway activation. This distinction is fundamental and clinically critical because it determines whether BCR-ABL-targeted TKIs are useful.
• ❌ B: Ph-negative MPNs have no BCR-ABL1 by any method - that is the definition.
• ❌ C: CML is Ph-positive in >90% by cytogenetics and 100% by PCR/FISH. There is no BCR-ABL-negative CML.
• ❌ D: JAK2 mutations are the hallmark of PV (>95%) and ET/PMF - NOT CML.
• ❌ E: Ph chromosome (BCR-ABL1) is found in both CML (~95%) and a subset of ALL (~25% of adult ALL, especially B-ALL).

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Vignette 23 - Hydroxyurea Side Effects

• A) Vitamin B12 deficiency from PV; supplement B12
• B) Hydroxyurea toxicity (mucocutaneous ulcers, macrocytosis); switch to ruxolitinib or interferon-alpha
• C) Transformation to MDS; bone marrow biopsy urgently
• D) Iron deficiency from phlebotomy; supplement iron
• E) Folate deficiency; supplement folic acid

• ✅ B is correct. Hydroxyurea (ribonucleotide reductase inhibitor) commonly causes:
  • Macrocytosis (inhibits DNA synthesis - megaloblastic-like effect)
  • Mucocutaneous ulcers - oral and leg ulcers are a classic, troublesome side effect
  • Myelosuppression (anemia, neutropenia)
  • Skin hyperpigmentation, nail changes When these toxicities occur, the patient is classified as intolerant of hydroxyurea, and alternative cytoreductive agents are indicated: ruxolitinib (FDA-approved for HU-refractory/intolerant PV) or interferon-alpha (preferred in younger patients/pregnancy).
• ❌ A: B12 deficiency causes macrocytosis but not leg ulcers in this context. The temporal relationship with hydroxyurea is key.
• ❌ C: MDS transformation is possible in PV (especially with cytotoxic therapy) but would require bone marrow biopsy and typically presents with cytopenias + dysplastic changes, not ulcers.
• ❌ D/E: Iron deficiency causes microcytosis (MCV low); folate causes macrocytosis but not the ulcers.

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Vignette 24 - Myelofibrosis vs CML: Key Differentiator

• A) Serum EPO level
• B) JAK2 V617F PCR
• C) BCR-ABL1 PCR
• D) Bone marrow biopsy
• E) Peripheral blood FISH for del(13q)

• ✅ C is correct. BCR-ABL1 PCR is positive in CML (Patient B) and negative in PMF (Patient A). This is the single most important test to distinguish CML from other MPNs including PMF. Both can have leukocytosis and splenomegaly, but:
  • PMF: Teardrop cells, NRBCs, marrow fibrosis, JAK2/CALR/MPL mutations → BCR-ABL1 negative
  • CML: Full granulocytic spectrum, basophilia, low LAP → BCR-ABL1 positive
• ❌ A: EPO differentiates PV from secondary polycythemia, not PMF from CML.
• ❌ B: JAK2 V617F can be positive in PMF but is also positive in PV and ET; it does not definitively diagnose or exclude CML.
• ❌ D: Bone marrow biopsy shows fibrosis in PMF vs. hypercellular granulocytic hyperplasia in CML - useful, but molecular testing is faster and more definitive.

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Vignette 25 - Reactive vs Clonal Thrombocytosis

• A) Essential thrombocythemia
• B) CML
• C) Reactive thrombocytosis (post-splenectomy + iron deficiency)
• D) Polycythemia vera
• E) Primary myelofibrosis

• ✅ C is correct. Reactive (secondary) thrombocytosis has common causes:
  • Post-splenectomy - the spleen normally sequesters ~1/3 of platelets; after removal, platelet count rises sharply
  • Iron deficiency - a well-recognized cause of thrombocytosis
  • Infection, inflammation, malignancy, tissue injury Reactive thrombocytosis does NOT carry the same thrombotic/hemorrhagic risk as clonal ET. Platelets are functionally normal. JAK2/CALR/MPL will be negative. There are no giant platelets or bone marrow clonal changes.
• ❌ A: ET is a diagnosis of exclusion. Young age, clear precipitants (splenectomy + iron deficiency), and absence of clonal markers make ET unlikely here.
• ❌ B: CML would show leukocytosis with the granulocytic spectrum, basophilia, and BCR-ABL1 positivity.
• ❌ D: PV requires elevated Hgb/Hct - not present here.
• ❌ E: PMF presents with cytopenias, fibrosis, and leukoerythroblastic smear, not isolated thrombocytosis in a young trauma patient.

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SECTION 6: TRANSFORMATION, COMPLICATIONS, AND SPECIAL SCENARIOS

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Vignette 26 - MPN Transformation to AML

• A) Richter transformation to DLBCL; moderately good prognosis
• B) Post-PV myelofibrosis (spent phase); treat with ruxolitinib
• C) Transformation to AML (blast phase); very poor prognosis, median survival months
• D) Secondary MDS; lenalidomide is first-line
• E) CML transformation; start imatinib

• ✅ C is correct. Approximately 1-2% of PV patients transform to AML (accelerated or blast transformation). Risk is increased by cytotoxic therapy (alkylating agents > hydroxyurea) and disease duration. Post-PV AML carries a very poor prognosis - median survival 2-6 months, with complex karyotype adding further adverse features. Treatment is difficult; outcomes with standard AML induction are poor. Allogeneic HSCT if feasible offers the only potential for cure.
• ❌ A: Richter transformation (CLL → DLBCL) is specific to CLL, not PV.
• ❌ B: Post-PV myelofibrosis (spent phase) does not show 35% blasts; it shows marrow fibrosis with leukoerythroblastosis.
• ❌ D: MDS requires <20% blasts. ≥20% blasts (35% here) defines AML.
• ❌ E: PV does not transform to CML; BCR-ABL1 would still be negative.

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Vignette 27 - CML in Pregnancy

• A) Continue imatinib - it is safe in all trimesters
• B) Stop imatinib immediately; switch to interferon-alpha for the first trimester
• C) Stop all therapy; disease will not progress during pregnancy
• D) Perform emergency HSCT before delivery
• E) Switch to dasatinib, which is safer in pregnancy

• ✅ B is correct. All BCR-ABL1 TKIs (imatinib, dasatinib, nilotinib, bosutinib, ponatinib) are teratogenic (Category D or X) and must be avoided, especially in the first trimester (organogenesis). Interferon-alpha does not cross the placenta and is the preferred cytoreductive agent during pregnancy for CML and other MPNs. Management depends on response depth:
  • If in deep molecular response (MR4/MR4.5) before conception: TKI-free interval may be tolerable with close monitoring
  • If disease requires treatment: interferon-alpha is the safe option
• ❌ A: Imatinib causes fetal malformations - it must be stopped.
• ❌ C: CML can progress during pregnancy without treatment, potentially to accelerated/blast phase.
• ❌ D: Emergency HSCT is not indicated in this stable scenario.
• ❌ E: Dasatinib is also teratogenic; ALL TKIs are contraindicated in early pregnancy.

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Vignette 28 - TKI Side Effect Profile

• A) Pneumonia; treat with antibiotics
• B) Congestive heart failure from dasatinib cardiomyopathy; stop dasatinib permanently
• C) Dasatinib-induced pleural effusion; hold dasatinib, add diuretics ± steroids, then resume at lower dose or switch TKI
• D) Pulmonary embolism; start anticoagulation
• E) Nilotinib-induced QTc prolongation causing cardiac failure

• ✅ C is correct. Pleural effusion is the most characteristic and common serious adverse effect of dasatinib (seen in 10-35% of patients), caused by its inhibition of PDGFR and SRC kinases affecting pleural fluid homeostasis. Management:
  1. Hold dasatinib temporarily
  2. Thoracentesis if large/symptomatic
  3. Diuretics and/or short course of steroids
  4. Resume at lower dose or switch to another TKI (nilotinib, bosutinib)
• ❌ A: No fever, no infiltrate - pneumonia is unlikely. Antibiotics are not the answer.
• ❌ B: Dasatinib does not typically cause cardiomyopathy. This is a drug-specific side effect, not permanent cardiac damage.
• ❌ D: PE is possible but the clinical context (new TKI, unilateral effusion without DVT symptoms) points strongly to dasatinib toxicity.
• ❌ E: Nilotinib's characteristic toxicity is QTc prolongation, arterial occlusive events, and pancreatitis - not pleural effusion.

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Vignette 29 - Treatment-Free Remission (TFR) in CML

• A) TFR is not possible; CML patients must stay on TKIs for life
• B) TFR can be attempted after ≥2 years of sustained MR4.5; ~50% maintain remission; relapsers respond to TKI rechallenge
• C) TFR requires allogeneic HSCT first to confirm cure
• D) TFR is only possible after switching to asciminib
• E) Any patient achieving MMR (MR3) can stop therapy

• ✅ B is correct. TFR is a validated goal in CML management. Requirements:
  • Sustained MR4.5 for ≥2 years (some guidelines require ≥3 years)
  • On a TKI for adequate duration (typically ≥5 years total)
  • Close molecular monitoring (monthly qPCR for 1 year after stopping)
  • ~40-60% of eligible patients maintain TFR at 1 year
  • Most relapses occur in the first 6 months and are universally responsive to TKI rechallenge
  • TFR eliminates drug costs and side effects and is particularly valuable for young patients/women desiring pregnancy.
• ❌ A: TFR is well-established and endorsed by ELN and NCCN guidelines.
• ❌ C: HSCT is not required for TFR; molecular remission on TKIs is sufficient.
• ❌ D: TFR has been demonstrated with imatinib (STIM trial), nilotinib (ENESTfreedom), dasatinib, and others - not only asciminib.
• ❌ E: MMR alone (BCR-ABL1 ≤0.1%) is insufficient; deeper MR4.5 is required for TFR to be safe.

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Vignette 30 - Integrated MPN Final Challenge

• A) He has developed ET; stop phlebotomy and observe
• B) Iron deficiency from phlebotomy is masking PV progression; his rising WBC/platelets suggest disease progression requiring cytoreduction; start hydroxyurea and treat erythromelalgia with aspirin
• C) He has transformed to CML; send BCR-ABL1
• D) He has developed PMF; start ruxolitinib
• E) His response is optimal; continue phlebotomy alone

• ✅ B is correct. This integrates multiple key PV concepts:
  1. Iron deficiency from phlebotomy is intentionally induced to limit erythropoiesis, but it may mask the full picture of PV (suppressed Hgb despite continued clonal activity). The WBC and platelets continuing to rise confirms ongoing clonal myeloproliferation.
  2. Rising WBC >10,000 and platelets >1,000,000 = disease not adequately controlled by phlebotomy alone → cytoreduction is now indicated.
  3. Burning pain in feet = erythromelalgia from platelet microvascular occlusion → low-dose aspirin (dramatic relief).
  4. High-risk criteria also met (age 59 = near threshold, rising counts) → hydroxyurea as first-line cytoreduction.
• ❌ A: ET diagnosis cannot be made in a patient with confirmed PV (JAK2+, previously elevated Hgb/Hct). Iron deficiency from phlebotomy has lowered the Hgb, not cured the disease.
• ❌ C: PV does not transform to CML. BCR-ABL1 testing is not warranted here.
• ❌ D: No teardrop cells, no marrow fibrosis described - PMF transformation has not occurred.
• ❌ E: Phlebotomy alone is failing to control the myeloproliferative drive (rising WBC, platelets, erythromelalgia). Cytoreduction is overdue.

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Quick Reference: Topics Covered Across the 30 Vignettes

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30 Clinical Vignettes: Polycythemia Vera & Essential Thrombocythemia

Final Year Level | Complete Answer Explanations

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PART 1: POLYCYTHEMIA VERA (15 Vignettes)

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Vignette 1 - Classic Presentation

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✅ ANSWER: B - Polycythemia Vera

• ❌ A (Sleep apnea/secondary polycythemia): Secondary causes have elevated EPO (compensatory response to hypoxia) and isolated RBC elevation - WBC and platelets are normal. Aquagenic pruritus does not occur.
• ❌ C (ET): ET has markedly elevated platelets as the dominant feature; Hgb/Hct are normal.
• ❌ D (CML): CML presents with extreme leukocytosis (WBC often >100,000) with the full granulocytic spectrum, basophilia, and BCR-ABL1 positivity. The EPO is not the key marker.
• ❌ E (Relative polycythemia): Relative/spurious polycythemia occurs due to plasma volume contraction (dehydration, diuretics). WBC and platelets are normal; EPO is normal; no aquagenic pruritus or splenomegaly.

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Vignette 2 - PV Diagnostic Criteria

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✅ ANSWER: B - Yes, two major criteria are sufficient

• Major criteria: (1) Hgb >16.5 g/dL (M) or >16.0 g/dL (F), or Hct >49% (M) or >48% (F); (2) Bone marrow hypercellularity with panmyelosis; (3) JAK2 V617F or JAK2 exon 12 mutation
• Minor criterion: Subnormal serum EPO

• ❌ A: Bone marrow biopsy is required when Hgb/Hct does not reach the threshold but JAK2 is positive, or when polycythemia vera is suspected without a clear molecular marker. It is not always mandatory first.
• ❌ C: JAK2 V617F is present in >97% of PV; it is highly specific for clonal erythrocytosis in the right context.
• ❌ D: BCR-ABL1 exclusion is part of the PV workup, but it is not a criterion that must be stated as positive/negative to make the PV diagnosis. Excluding CML is implicit.
• ❌ E: Low EPO supports the diagnosis - it is a minor criterion. A normal EPO would argue against PV (or at least require further workup), but low EPO is not required if all 3 major criteria are met.

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Vignette 3 - PV Pathogenesis

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✅ ANSWER: B - JAK2 V617F → constitutive JAK-STAT activation → EPO-independent proliferation → suppressed EPO

• ❌ A: PV does not directly damage the kidneys. Renal involvement may occur from hyperviscosity complications, but this is not the mechanism of low EPO.
• ❌ C: EPO receptor downregulation from high Hgb is not the established mechanism in PV.
• ❌ D: Bone marrow fibrosis is a late complication of PV (spent phase), not the mechanism of low EPO at diagnosis.
• ❌ E: Anti-EPO antibodies cause pure red cell aplasia (low Hgb), the opposite of PV.

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Vignette 4 - PV vs Relative Polycythemia

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✅ ANSWER: B - Relative/Spurious Polycythemia (Gaisbock Syndrome)

• ❌ A (PV): JAK2 V617F is negative and EPO is normal. PV requires JAK2 positivity or low EPO + bone marrow panmyelosis.
• ❌ C (Secondary COPD): Secondary polycythemia from COPD would have elevated EPO and may show signs of chronic lung disease (cor pulmonale, reduced spirometry). It is possible in a smoker, but normal EPO + normal WBC/platelets in a plethoric obese/alcohol-drinking patient with no pulmonary symptoms points to relative polycythemia.
• ❌ D: ET does not cause elevated Hct as a primary feature.
• ❌ E (Chuvash polycythemia): This is a rare autosomal recessive condition due to VHL mutations causing high-affinity EPO sensing. It is congenital, typically presents in childhood/young adulthood, and EPO is elevated - not the picture here.

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Vignette 5 - PV and Thrombosis

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✅ ANSWER: B - TIA from PV-related hyperviscosity and thrombosis

1. Increased blood viscosity from elevated RBC mass → sluggish flow and vascular sludging
2. Thrombocytosis with dysfunctional platelets → paradoxical tendency to both thrombose and bleed
3. Basophilia and histamine contribute to vascular reactivity

• ❌ A: PV causes thrombocytosis (elevated platelets), not thrombocytopenia. Hemorrhagic events do occur but TIAs are thrombotic.
• ❌ C: PFO-related paradoxical emboli require a venous source. While possible, this ignores the direct PV pathophysiology.
• ❌ D: While AF is common in the elderly, this patient's PV with elevated viscosity is the most likely culprit. PV management must be addressed regardless.
• ❌ E: Hyperviscosity from IgM paraprotein occurs in Waldenström macroglobulinemia (plasma cell/lymphoplasmacytic neoplasm), causing hyperviscosity syndrome with very different lab findings (elevated IgM, normal RBC mass).

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Vignette 6 - PV Risk Stratification

• Patient A: 55 years old, no prior thrombosis, no cardiovascular risk factors
• Patient B: 72 years old, prior DVT 2 years ago, hypertension

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✅ ANSWER: B - Risk-stratified treatment

• High-risk: Age ≥60 OR history of thrombosis
• Low-risk: Age <60 AND no prior thrombosis

• ❌ A: Over-treating low-risk PV with hydroxyurea exposes the patient to unnecessary toxicity (myelosuppression, leg ulcers, macrocytosis) without proven additional benefit.
• ❌ C: Allogeneic HSCT is not standard for PV; it is reserved for post-PV myelofibrosis or AML transformation in selected patients.
• ❌ D: No treatment for low-risk is too passive - phlebotomy + aspirin is still required for all PV patients to prevent vascular complications.
• ❌ E: Ruxolitinib is FDA-approved for PV refractory to or intolerant of hydroxyurea - it is second-line, not first-line.

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Vignette 7 - PV Treatment Target

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✅ ANSWER: B - Target Hct <45% in both men and women

• ❌ A: A target of <50% was used historically but is now known to be insufficient - the CYTO-PV trial clearly showed <45% is superior.
• ❌ C: There is no sex-based differential in the Hct target for treatment. The diagnostic thresholds differ by sex (>16.5 g/dL M, >16.0 g/dL F) but the treatment target Hct <45% is the same.
• ❌ D: A target of <40% is overly aggressive and risks iron deficiency anemia, fatigue, and reduced quality of life without additional benefit.
• ❌ E: While symptoms guide treatment frequency, the Hct <45% target is evidence-based and should be the objective regardless of symptom status.

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Vignette 8 - PV Hydroxyurea Indication and Toxicity

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✅ ANSWER: B - Hydroxyurea toxicity; switch to ruxolitinib or interferon-alpha

• Mucocutaneous ulcers (oral and particularly leg ulcers over malleoli) - a characteristic and treatment-limiting side effect
• Macrocytosis (ribonucleotide reductase inhibition impairs DNA synthesis, mimicking megaloblastic changes)
• Skin hyperpigmentation, nail changes, squamous cell carcinoma risk with prolonged use
• Myelosuppression (anemia, neutropenia)

• Ruxolitinib - FDA-approved for HU-refractory/intolerant PV; reduces Hct, controls symptoms, improves quality of life
• Interferon-alpha (pegylated) - preferred in younger patients, pregnancy; can achieve molecular remission of JAK2 allele burden

• ❌ A (AML transformation): AML presents with cytopenias AND high blast count (≥20%). No mention of blasts here, and the clinical picture is clearly drug toxicity.
• ❌ C: While leg ulcers can occur with venous insufficiency, the combination with oral ulcers and macrocytosis in a patient on long-term hydroxyurea strongly points to drug toxicity, not venous insufficiency alone.
• ❌ D: B12 deficiency causes macrocytosis but NOT leg ulcers in this pattern. The causal relationship to hydroxyurea is clear.
• ❌ E: Stopping all therapy in PV without replacement risks rebound polycythemia and thrombosis.

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Vignette 9 - PV and Gout

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✅ ANSWER: B - High cell turnover → hyperuricemia; treat with allopurinol

• ❌ A: While diet plays a role, the primary mechanism is endogenous uric acid overproduction from cell turnover - dietary restriction alone is insufficient.
• ❌ C: Low-dose aspirin (81 mg) does NOT meaningfully inhibit uric acid excretion (that effect is at higher analgesic/anti-inflammatory doses ≥2-3 g/day). Stopping aspirin would increase thrombotic risk dramatically in PV.
• ❌ D: Gout in PV has a specific mechanism (high cell turnover). Colchicine treats the acute attack, but allopurinol is needed for prevention.
• ❌ E: Phlebotomy does release some cell contents, but it is not the primary driver of gout. Reducing phlebotomy to "manage gout" would be dangerous, allowing Hct to rise and increasing thrombotic risk.

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Vignette 10 - PV and Peptic Ulcer Disease

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✅ ANSWER: C - Histamine from basophils stimulates gastric acid secretion

• ❌ A: PV does not directly stimulate parietal cells independent of histamine.
• ❌ B: No direct evidence that elevated RBC mass damages the gastric mucosa.
• ❌ D: Iron deficiency from phlebotomy affects RBC size (microcytosis), not gastric mucosa directly.
• ❌ E: EPO has no known role in H. pylori susceptibility or gastric mucosal protection.

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Vignette 11 - PV in Pregnancy

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✅ ANSWER: C - Phlebotomy + low-dose aspirin + interferon-alpha if needed; avoid hydroxyurea

• Phlebotomy is safe throughout pregnancy (target Hct <45%)
• Low-dose aspirin (81 mg) is recommended - reduces placental thrombosis risk (category B; used safely in pregnancy for preeclampsia prophylaxis)
• Hydroxyurea is teratogenic (causes fetal malformations - limb defects, neural tube defects) and is absolutely contraindicated in pregnancy
• Interferon-alpha does not cross the placenta (large molecule), is safe in pregnancy, and is the preferred cytoreductive agent when needed
• PV in pregnancy carries high-risk for both maternal (thrombosis, hemorrhage) and fetal complications (miscarriage, growth restriction)

• ❌ A: Hydroxyurea is teratogenic (FDA Category D) - CONTRAINDICATED in pregnancy. This is a critical safety point.
• ❌ B: Low-dose aspirin is actually recommended in PV pregnancy to reduce thrombotic complications; the statement to avoid it entirely is incorrect.
• ❌ D: Pregnancy in PV is high-risk but not contraindicated. With appropriate management (multidisciplinary care), successful outcomes are achievable.
• ❌ E: Erythrocytapheresis may be used in selected cases but is not routine weekly management for PV in pregnancy.

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Vignette 12 - Post-PV Myelofibrosis

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✅ ANSWER: B - Post-PV myelofibrosis; treat with ruxolitinib

• Paradoxical fall in Hgb (marrow replaced by fibrosis, no longer producing RBCs effectively)
• Massive splenomegaly from extramedullary hematopoiesis compensating for failed marrow
• Leukoerythroblastic blood smear: teardrop cells (dacryocytes - shaped by splenic passage), nucleated RBCs, immature granulocytes
• Dry tap on aspiration + dense marrow fibrosis on biopsy
• Constitutional symptoms (B symptoms)

• ❌ A: Increasing phlebotomy in a patient with already low Hgb (9.8) would be harmful and is completely inappropriate. The PV has transformed.
• ❌ C: PV does not transform to CML. BCR-ABL1 does not arise from a JAK2-driven clone.
• ❌ D: Iron deficiency causes microcytic anemia, not the full leukoerythroblastic picture with teardrop cells and marrow fibrosis.
• ❌ E: Aplastic anemia has a hypocellular (empty) marrow, not a fibrotic one. There is no prior PV history in aplastic anemia.

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Vignette 13 - PV and Budd-Chiari Syndrome

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✅ ANSWER: B - Test for JAK2 V617F (evaluate for underlying PV)

• ❌ A: Liver biopsy might be needed eventually, but the priority is identifying the underlying thrombophilic cause, as PV is highly treatable and changes long-term management dramatically.
• ❌ C: Factor V Leiden and other thrombophilias should also be tested, but PV/MPNs are the most common single cause of Budd-Chiari and should be prioritized.
• ❌ D: Doppler has already confirmed the diagnosis. CT angiography adds radiation without changing the urgent diagnostic priority.
• ❌ E: Anticoagulation is important for management but must be paired with identifying the underlying cause. Discharging without PV workup would miss a life-threatening and treatable condition.

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Vignette 14 - Aquagenic Pruritus Mechanism

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✅ ANSWER: C - Histamine from basophils; antihistamines or aspirin

• Antihistamines (H₁ blockers) - first-line for symptoms
• Low-dose aspirin - effective via COX inhibition affecting mast cell/basophil activation
• Ruxolitinib - dramatically reduces pruritus by suppressing JAK-STAT-driven basophil proliferation
• Paroxetine (SSRI) - second-line option (mechanism unclear but clinically effective)
• Best long-term solution: cytoreductive therapy to control the neoplastic clone

• ❌ A: Dry skin occurs in iron deficiency or dehydration but does not cause the characteristic burning water-triggered pattern. Moisturizers would not help.
• ❌ B: Iron deficiency from phlebotomy can cause pruritus (diffuse, not aquagenic). But this patient has newly diagnosed PV and hasn't had phlebotomy-induced iron deficiency yet.
• ❌ D: IgE-mediated allergy causes urticaria (hives). Aquagenic pruritus in PV has no IgE mechanism.
• ❌ E: Phlebotomy reduces viscosity and may help indirectly over time but does not address the immediate histamine-mediated symptom.

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Vignette 15 - PV Long-Term Outcome

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✅ ANSWER: B - Median survival ~10 years; 15-20% post-PV MF; 1-2% AML

• Without treatment: Death from vascular complications within months
• With phlebotomy alone: Median survival ~10 years (Robbins)
• Modern therapy (phlebotomy + cytoreduction + aspirin): 5-year survival >90%; thrombotic death markedly reduced
• Transformation to post-PV myelofibrosis: ~15-20% after average 10 years
• Transformation to AML: ~1-2% (rare but poor prognosis when it occurs; risk is higher with alkylating agent exposure)
• Today, most PV patients die of cardiovascular complications rather than transformation

• ❌ A: PV with treatment has excellent prognosis - 5-year survival exceeds 90% with modern management.
• ❌ C: No treatment is curative for PV (except possibly allogeneic HSCT in selected post-PV MF cases). Hydroxyurea controls the disease but does not eradicate the clone or prevent transformation.
• ❌ D: HSCT in all PV patients would cause unacceptable treatment-related mortality for a disease with >90% 5-year survival on medical management.
• ❌ E: AML transformation occurs in only ~1-2% of PV patients; it is not inevitable. The more common late complication is post-PV myelofibrosis (15-20%).

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PART 2: ESSENTIAL THROMBOCYTHEMIA (15 Vignettes)

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Vignette 16 - ET Classic Presentation

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✅ ANSWER: B - Essential Thrombocythemia with erythromelalgia

• ❌ A (Reactive thrombocytosis): Reactive causes (iron deficiency, inflammation) produce smaller, morphologically normal platelets. Giant platelets suggest a clonal process. Erythromelalgia does not occur in reactive thrombocytosis.
• ❌ C (CML): CML has marked leukocytosis (often >100,000), basophilia, left shift, and BCR-ABL1 positivity. Normal WBC excludes CML here.
• ❌ D (PMF): PMF presents with cytopenias, teardrop cells, leukoerythroblastic picture, and marrow fibrosis - not isolated thrombocytosis in a young woman.
• ❌ E (SLE): SLE causes thrombocytopenia (low platelets), not thrombocytosis. SLE could cause arthralgia, rash, serositis.

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Vignette 17 - ET Molecular Workup

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✅ ANSWER: B - Test CALR exon 9 and MPL W515 mutations

• JAK2 V617F: ~50-60%
• CALR (calreticulin) exon 9 frameshift: ~25-35%
• MPL W515L/K: ~5-10%
• Triple-negative (no JAK2/CALR/MPL): ~5-10%

• ❌ A: BCR-ABL1 exclusion is part of ET workup (one of the major criteria is "not CML"), but the question asks what to do AFTER JAK2 is negative, and BCR-ABL should already be checked as part of the workup alongside JAK2.
• ❌ C: FLT3/NPM1 are AML markers with no role in ET diagnosis.
• ❌ D: TP53 testing has prognostic value in some MPN/MDS contexts but is not part of primary ET diagnosis criteria.
• ❌ E: Bone marrow biopsy establishes morphology, but molecular clonal markers are required diagnostic criteria by WHO/ICC. A CALR or MPL mutation fulfills a major criterion; missing it would mean incomplete workup.

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Vignette 18 - CALR vs JAK2 in ET: Clinical Differences

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✅ ANSWER: B - JAK2+ = higher Hgb/WBC/thrombotic risk; CALR+ = higher platelets, lower thrombotic risk

• ❌ A: The opposite is true - JAK2+ ET carries higher thrombotic risk.
• ❌ C: The mutations have distinct clinical profiles with meaningful differences in risk stratification.
• ❌ D: CALR+ ET generally has a more favorable prognosis than JAK2+ ET.
• ❌ E: No sex-specific mutation distribution exists in ET.

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Vignette 19 - ET and Extreme Thrombocytosis: Paradoxical Bleeding

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✅ ANSWER: B - Acquired VWD; reduce platelets before surgery

• Low ristocetin cofactor activity (<30% is diagnostic)
• Absent high-molecular-weight VWF multimers on analysis
• Paradoxically high platelets but bleeding tendency from loss of functional VWF

• ❌ A: Platelets are massively elevated, not low. Transfusing more platelets worsens aVWD.
• ❌ C: IVIG treats immune thrombocytopenia (ITP, low platelets from immune destruction) - not applicable here.
• ❌ D: Vitamin K deficiency affects factors II, VII, IX, X. This patient's picture is specifically VWF-related.
• ❌ E: DIC involves consumption coagulopathy (low fibrinogen, elevated D-dimer, thrombocytopenia). The platelet count here is extremely high, excluding DIC.

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Vignette 20 - ET Diagnosis: Exclusion of Reactive Causes

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✅ ANSWER: B - Treat reversible causes first; then reassess

• Post-splenectomy (no splenic platelet sequestration)
• Iron deficiency (a well-recognized cause of thrombocytosis)
• Inflammation/infection (elevated CRP = inflammatory state driving reactive megakaryocytopoiesis via IL-6 → thrombopoietin)

1. Sustained platelet count ≥450,000/µL
2. NOT meeting criteria for PV, PMF, MDS, or CML
3. Reactive causes excluded

• ❌ A: Jumping to ET workup without addressing obvious reactive causes leads to overdiagnosis and potential harm from unnecessary cytoreductive therapy.
• ❌ C: Post-splenectomy thrombocytosis is often transient and decreases over months. It is NOT always permanent and does not automatically mean ET.
• ❌ D: Platelet count alone is insufficient. The WHO/ICC requires multiple criteria including exclusion of reactive causes and bone marrow/molecular confirmation.
• ❌ E: CRP elevation suggests inflammation (a reactive cause) - not ET specifically. ET itself does not typically elevate CRP.

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Vignette 21 - ET Thrombosis Risk Score

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✅ ANSWER: C - Very high-risk; hydroxyurea + aspirin

• ❌ A: Low-risk applies to young (<60), JAK2-negative, thrombosis-free patients. This patient is the opposite.
• ❌ B: Intermediate-risk management would under-treat this very high-risk patient.
• ❌ D: Thrombosis risk scoring uses age, JAK2 status, and prior thrombosis - CALR status is not a component of IPSET scoring (though CALR+ generally has lower risk).
• ❌ E: Age alone places him in high-risk, but the additional prior thrombosis and JAK2+ status makes him very high-risk requiring cytoreduction, not aspirin alone.

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Vignette 22 - ET Bone Marrow Morphology

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✅ ANSWER: B - Confirms ET; PMF has small hypolobulated megakaryocytes with fibrosis

• ❌ A: PMF megakaryocytes are the opposite - small with cloud-like nuclei and associated with dense fibrosis. This biopsy shows ET features.
• ❌ C: Megakaryocyte morphology is a major criterion in the WHO/ICC diagnostic classification of MPNs.
• ❌ D: CML megakaryocytes are small and hypolobulated (similar to PMF), not the staghorn pattern.
• ❌ E: AML-M7 (acute megakaryoblastic leukemia) has megakaryoblasts (≥20% blasts of megakaryocytic lineage), CD41/CD61 positivity - a completely different entity.

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Vignette 23 - ET and Pregnancy Complications

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✅ ANSWER: B - Aspirin + LMWH + interferon-alpha; avoid hydroxyurea

• First-trimester loss: Placental microvascular thrombosis from platelet aggregates
• Later complications: Placental infarction, abruption, IUGR, stillbirth
• Maternal: DVT, PE, thrombotic events

1. Low-dose aspirin (reduces placental thrombosis)
2. LMWH (subcutaneous heparin - safe in pregnancy, does not cross placenta) - for anticoagulation given prior losses
3. Interferon-alpha (if cytoreduction needed - safe, does not cross placenta)
4. Hydroxyurea is ABSOLUTELY CONTRAINDICATED in pregnancy (teratogenic)
5. Anagrelide is also contraindicated in pregnancy

• ❌ A: ET is a proven cause of recurrent pregnancy loss; ignoring it is negligent.
• ❌ C: Hydroxyurea = teratogenic (contraindicated). Warfarin crosses the placenta and causes warfarin embryopathy (nasal hypoplasia, stippled epiphyses, CNS anomalies) - contraindicated in first trimester.
• ❌ D: Therapeutic abortion is not routinely recommended. With proper management, successful pregnancy is achievable.
• ❌ E: Platelet transfusion would worsen thrombosis in a patient with already extreme thrombocytosis and dysfunction.

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Vignette 24 - ET: First-Line Cytoreductive Agent

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✅ ANSWER: C - Hydroxyurea + low-dose aspirin

• Inhibits ribonucleotide reductase → reduces DNA synthesis in rapidly dividing cells
• Effectively reduces platelet count to target (<400,000-600,000/µL)
• Well-tolerated in most patients
• Target: platelet count <400,000/µL ideally; at minimum <600,000/µL

• ❌ A (Anagrelide): Anagrelide is a second-line option (when hydroxyurea fails or is intolerant). It selectively inhibits megakaryocyte differentiation. The PT-1 trial showed it was inferior to hydroxyurea as first-line.
• ❌ B (Busulfan): Busulfan is an alkylating agent with leukemogenic potential. It is used in elderly patients or when other agents fail - not first-line.
• ❌ D (Ruxolitinib): Ruxolitinib is used in PV refractory to HU and in myelofibrosis; it is not standard first-line for ET.
• ❌ E (Interferon-alpha): IFN-α is preferred in young patients (<40) and pregnant women. For a 70-year-old post-thrombosis patient, hydroxyurea is preferred as it is better tolerated and has robust trial data.

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Vignette 25 - ET vs Prefibrotic PMF

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✅ ANSWER: B - Prefibrotic PMF; worse prognosis than ET

• Clinically resembles ET (thrombocytosis, mild splenomegaly, few symptoms)
• Histologically differs: Small, immature megakaryocytes with cloud-like/hypolobulated nuclei, tight perisinusoidal clustering, mild reticulin fibrosis (MF-0 to MF-1) - the opposite of ET's large staghorn megakaryocytes
• Has significantly worse outcomes: Higher rate of progression to overt fibrotic PMF (25-30% vs <5% in ET), lower overall survival, higher transformation to AML
• Management differs: More aggressive monitoring; earlier consideration of cytoreduction and HSCT evaluation

• ❌ A: Prognosis and outcomes are NOT the same. Prefibrotic PMF has median survival of 15 years vs >20 years in ET. The distinction matters significantly for counseling and follow-up intensity.
• ❌ C: Nothing here suggests masked PV (iron deficiency hiding true erythrocytosis). EPO level and JAK2 status would clarify.
• ❌ D: Giant/abnormal megakaryocytes with clustering on biopsy are never "reactive."
• ❌ E: CML features are absent (no leukocytosis, no basophilia, no BCR-ABL1 indication from this picture).

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Vignette 26 - Anagrelide Mechanism and Use

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✅ ANSWER: C - Inhibits PDE-III → impairs megakaryocyte maturation → fewer platelets

• Selective for platelets (unlike hydroxyurea which affects all rapidly dividing cells)
• Advantages: Useful when HU-intolerant, no leukemogenic potential
• Disadvantages: Cardiac side effects (palpitations, fluid retention, arrhythmia - from PDE-III inhibition in cardiac muscle), headaches, diarrhea
• Contraindicated in cardiac disease
• Not recommended in pregnancy (limited safety data)
• Second-line in most guidelines

• ❌ A: This describes hydroxyurea's mechanism (ribonucleotide reductase inhibition).
• ❌ B: JAK1/2 inhibition is the mechanism of ruxolitinib.
• ❌ D: No cytotoxic/complement-mediated platelet destruction mechanism is involved.
• ❌ E: MPL receptor blockade is not the mechanism; anagrelide works downstream at the intracellular signaling level (PDE-III inhibition).

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Vignette 27 - ET: Venous Sinus Thrombosis

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✅ ANSWER: C - ET/PV - unusual site thrombosis; send JAK2/CALR/MPL

• Splanchnic vein thrombosis (portal, hepatic, mesenteric - Budd-Chiari)
• Cerebral venous sinus thrombosis
• Retinal vein/artery thrombosis

• ❌ A, B, D: All thrombophilias should be tested, but the thrombocytosis of 960,000 strongly suggests an MPN as the primary etiology. Inherited thrombophilias (Factor V Leiden, protein C/S, antiphospholipid syndrome) do not explain thrombocytosis.
• ❌ E: Dehydration can contribute to CVST but does not explain extreme thrombocytosis. Discharging without investigating the thrombocytosis is dangerous.

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Vignette 28 - ET: Post-ET Myelofibrosis

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✅ ANSWER: B - Post-ET myelofibrosis; ruxolitinib ± HSCT

• Falling platelet count (marrow fibrosis replaces megakaryopoiesis)
• Splenomegaly (extramedullary hematopoiesis)
• Constitutional symptoms (B symptoms)
• Leukoerythroblastic smear (teardrop cells, NRBCs, immature WBCs)
• Marrow fibrosis on biopsy (reticulin grade 2-3 or collagen fibrosis)

• ❌ A: This is disease transformation, not spontaneous resolution. The fibrotic marrow means worsening disease.
• ❌ C: Aplastic anemia has hypocellular (empty) marrow, not fibrotic marrow. The ET history makes MF transformation far more likely.
• ❌ D: Clonal evolution (acquiring new mutations) can occur but mutations don't "convert" from CALR to JAK2. Additional mutations in ASXL1, EZH2, or TP53 drive transformation to MF.
• ❌ E: Grade 3 reticulin fibrosis in the context of a known MPN is clonal, not reactive.

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Vignette 29 - ET: Aspirin and Paradoxical Thrombosis Risk

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✅ ANSWER: B - Check ristocetin cofactor activity; aspirin may worsen bleeding in aVWD

• The patient already has a hemostatic defect from aVWD
• Adding aspirin (which further impairs platelet function via COX-1 inhibition) may potentiate bleeding risk
• Check ristocetin cofactor activity (<30% = significant aVWD) before starting aspirin
• If aVWD is confirmed, reduce platelet count first with cytoreduction (hydroxyurea), then reassess for aspirin use

• ❌ A: Aspirin is not contraindicated in ET broadly - it is recommended for most ET patients. The concern is specific to extreme thrombocytosis with confirmed aVWD.
• ❌ C: Aspirin is used in both JAK2+ and JAK2- ET based on symptoms and risk stratification, not mutation status alone.
• ❌ D: Aspirin does not cause thrombocytopenia.
• ❌ E: Aspirin and hydroxyurea are commonly used together in high-risk ET - there is no dangerous interaction.

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Vignette 30 - Integrated ET Case

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✅ ANSWER: B - ET, Very High-Risk, Hydroxyurea + Aspirin

• Platelet count ≥450,000/µL (750,000) ✓
• JAK2 V617F positive ✓
• BCR-ABL1 negative (excludes CML) ✓
• Bone marrow: large hyperlobulated megakaryocytes, minimal fibrosis ✓ (ET morphology)
• Normal Hgb (excludes PV) ✓

• Hydroxyurea (first-line cytoreductive therapy for high/very high-risk ET)
• Low-dose aspirin (reduces microvascular and thrombotic events)
• Target platelet count <400,000-600,000/µL
• Monitor CBC every 3 months; bone marrow reassessment if symptoms change

• ❌ A: Low-risk management (observation) is completely inappropriate given a prior TIA and JAK2+ status. This patient requires cytoreduction.
• ❌ C: PV requires elevated Hgb (>16.0 in women) and/or elevated Hct (>48%). Her Hgb is 13.4 g/dL - normal. This is ET.
• ❌ D: PMF features (teardrop cells, marrow fibrosis, cytopenias, leukoerythroblastosis) are absent. The marrow shows ET morphology.
• ❌ E: Aspirin alone is insufficient for very high-risk ET with prior thrombosis. Cytoreduction is mandatory.

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Summary Reference Table