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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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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