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ESSAY ANSWERS: HEMATOLOGY

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Q1. Megaloblastic Anemia - Etiopathogenesis, Clinical Features, and Treatment

Definition

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ETIOLOGY

A. Vitamin B12 Deficiency

• Inadequate diet, strict vegetarianism/veganism (B12 is found only in animal products - meat, fish, milk, eggs)

• Intrinsic factor (IF) deficiency - Pernicious anemia (autoimmune destruction of parietal cells), total/partial gastrectomy
• Malabsorption states - Diffuse intestinal disease (lymphoma, systemic sclerosis), ileal resection, Crohn's ileitis
• Competitive uptake - Fish tapeworm (Diphyllobothrium latum), bacterial overgrowth in blind loops/diverticula
• Pancreatic insufficiency (prevents release of B12 from haptocorrin)
• Achlorhydria (B12 not released from food proteins)

• Pregnancy, hyperthyroidism, disseminated cancer, chronic infection

• Recreational nitrous oxide use (oxidizes and inactivates B12)

B. Folic Acid Deficiency

• Grossly deficient diet - chronic alcoholism, poverty, old age, infancy

• Malabsorption syndromes (sprue, infiltrative intestinal disease)
• Drugs: phenytoin (anticonvulsant), oral contraceptives

• Hemodialysis

• Pregnancy, infancy, chronic hemolytic anemia, disseminated cancer (increased cell turnover)

• Folic acid antagonists: methotrexate (inhibits dihydrofolate reductase)

C. Unresponsive to B12 or Folate Therapy

• Metabolic inhibitors of DNA synthesis (e.g., hydroxyurea, cytosine arabinoside)

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PATHOGENESIS

Role of Vitamin B12 and Folate

• B12-dependent reaction 1: Methylcobalamin serves as cofactor in conversion of homocysteine → methionine (by methionine synthase). In this process, N5-methyltetrahydrofolic acid (N5-methyl FH4) is converted to tetrahydrofolic acid (FH4).
• FH4 (via N5,10-methylene FH4) is required for conversion of dUMP → dTMP (thymidylate synthesis), a building block for DNA.
• B12 deficiency traps folate as N5-methyl FH4 ("folate trap hypothesis"), reducing available FH4 for thymidylate synthesis.
• B12-dependent reaction 2: Adenosylcobalamin is required for isomerization of methylmalonyl-CoA → succinyl-CoA. Deficiency leads to elevated methylmalonic acid (MMA) in blood and urine - a specific marker for B12 deficiency (absent in folate deficiency).

Result of Impaired DNA Synthesis

• All proliferating cells, especially rapidly dividing marrow precursors, are affected.
• Nuclear-cytoplasmic asynchrony: Cytoplasm matures normally (hemoglobin accumulates), but the nucleus remains immature (fine, open chromatin pattern).
• Most precursors undergo apoptosis in the marrow = ineffective hematopoiesis → pancytopenia despite hypercellular marrow.

Pernicious Anemia (Autoimmune B12 Deficiency)

• Autoimmune gastritis destroys gastric parietal cells → loss of intrinsic factor (IF) secretion
• Type I antibodies (75%): Block binding of B12 to IF
• Type II antibodies: Block binding of IF-B12 complex to cubilin (ileal receptor)
• Type III antibodies (85-90%): Against gastric H+/K+ ATPase (proton pump) - not specific (found in 50% of older adults with idiopathic gastritis)
• Primary mechanism: autoreactive T-cell injury to gastric mucosa
• Associated with other autoimmune diseases: Hashimoto's thyroiditis, Addison's disease

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MORPHOLOGY

Peripheral Blood

• Macro-ovalocytes (macrocytic, oval red cells) - highly characteristic
• Appear "hyperchromic" but MCHC is normal
• Marked anisocytosis and poikilocytosis
• Hypersegmented neutrophils - 5 or more lobes (normal: 3-4); any neutrophil with 6+ lobes is pathognomonic
• Low reticulocyte count (ineffective erythropoiesis)
• Pancytopenia in severe cases

Bone Marrow

• Markedly hypercellular (due to elevated EPO)
• Megaloblasts at all stages of erythroid development - large cells with finely dispersed ("open") nuclear chromatin, prominent nucleoli, but hemoglobinized cytoplasm
• Orthochromatic megaloblast: hemoglobin present, but nucleus NOT pyknotic (unlike normal normoblast)
• Giant metamyelocytes and band forms (granulocytic line also affected)
• Abnormally large megakaryocytes with multilobate nuclei

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CLINICAL FEATURES

Symptoms and Signs of Anemia

• Slowly progressive onset (large B12 stores last 3-5 years; folate stores last ~3-4 months)
• Pallor, easy fatigability, dyspnea on exertion, palpitations
• Lemon-yellow tinge (pallor + mild jaundice from ineffective erythropoiesis/hemolysis)

GI Features

• Atrophic glossitis - shiny, smooth, "beefy red" tongue (Hunter's glossitis) - due to mucosal megaloblastic change
• Anorexia, nausea, weight loss, diarrhea

Neurological Features (B12 deficiency ONLY - NOT with folate deficiency)

• Subacute combined degeneration (SCD) of the spinal cord - demyelination of dorsal (posterior) and lateral spinal columns
• Symptoms: symmetrical paresthesias (pins and needles) in hands and feet, loss of vibration and position sense, progressive weakness, spasticity, ataxia
• In severe cases: mental disturbances ("megaloblastic madness"), memory loss, depression
• Neurological symptoms may precede overt anemia; administering folate alone can worsen neurological damage

Specific Features of Pernicious Anemia

• Occurs mainly in older adults (peak 6th-7th decade), more common in Northern Europeans
• Associated with blood group A
• Often accompanied by other autoimmune diseases
• Fundic gland atrophy on gastric biopsy; gastric achlorhydria
• Increased risk of gastric carcinoma (3x risk) and gastric carcinoid

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LABORATORY FINDINGS

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TREATMENT

Treatment of Vitamin B12 Deficiency (Pernicious Anemia)

• Parenteral Vitamin B12 (Cyanocobalamin or Hydroxocobalamin):
  • Preferred route in pernicious anemia and malabsorption states (bypasses the gut)
  • Initial: 1000 mcg IM daily for 1 week, then weekly for 1 month, then monthly for life
  • Reticulocyte response occurs within 3-5 days (peak at 5-7 days)
  • Neurological improvement may take months and may be incomplete if damage is severe
• High-dose oral B12: Passive absorption (~1% of dose) can compensate in deficiency; feasible in dietary deficiency
• Folic acid supplementation may be given concurrently, but NEVER without B12 replacement (to avoid precipitating/worsening neurological disease)
• Lifelong treatment required for pernicious anemia
• Gastroprotection and monitoring for gastric carcinoma

Treatment of Folate Deficiency

• Oral Folic acid 5 mg/day for 4 months (or until deficiency is corrected; continue throughout pregnancy)
• Adequate reticulocyte response within 5-7 days
• Treat underlying cause (alcoholism, malabsorption, drug withdrawal)
• Folic acid does NOT correct neurological complications of B12 deficiency
• Prevention: Folic acid supplementation (400 mcg/day) for all women of childbearing age (prevents neural tube defects)

Monitoring Response

• Reticulocytosis within 3-5 days confirms diagnosis
• Hemoglobin rises; hypersegmented neutrophils disappear within 2 weeks
• Hypokalemia may occur with rapid red cell regeneration (K+ enters newly formed cells) - monitor and replace electrolytes

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Q2. Leukemoid Reaction and Differentiation from Chronic Myeloid Leukemia (CML)

LEUKEMOID REACTION

Definition

Types

1. Granulocytic type (most common) - resembles CML; WBC predominantly neutrophils and myeloid precursors
2. Lymphocytic type - resembles CLL; seen with viral infections (especially in children - infectious mononucleosis)

Causes of Granulocytic Leukemoid Reaction

• Infections: Severe bacterial infections (diphtheria, pertussis, tuberculosis, septicemia), Clostridium difficile disease
• Malignancy: Hodgkin's disease, carcinomatosis, marrow metastases
• Toxic/pharmacological: Corticosteroids, colony-stimulating factors (G-CSF, GM-CSF)
• Reactive conditions: Rebound granulocytosis (post-chemotherapy), severe hemorrhage, burns, tissue necrosis
• Hemolytic anemia (extreme regenerative response)

Peripheral Blood Features

• Marked leukocytosis (WBC >50,000/mm³)
• Left shift: Bands, metamyelocytes, myelocytes in circulation
• Toxic granulation in neutrophils (dark, coarse cytoplasmic granules)
• Döhle bodies (pale blue cytoplasmic inclusions)
• No basophilia or eosinophilia (in contrast to CML)
• Platelets and red cells usually normal or reactive

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CHRONIC MYELOID LEUKEMIA (CML)

Definition

Clinical Features of CML

• Median age at diagnosis: 57-60 years; slight male predominance
• Chronic phase (CP): Often insidious onset; up to 50% asymptomatic at diagnosis
  • Symptomatic: fatigue, weight loss, night sweats (hypermetabolism), abdominal discomfort
  • Massive splenomegaly - most distinctive feature; left upper quadrant pain (splenic infarction)
  • Hepatomegaly
• Accelerated phase: Worsening cytopenias, increasing blasts (10-20%), progressive splenomegaly
• Blast crisis (BC): Appearance of acute leukemia (>20% blasts); myeloid (70%) or lymphoid (30%) transformation; poor prognosis

Peripheral Blood in CML

• Leukocytosis (often >100,000/mm³ in chronic phase)
• Full spectrum of myeloid cells at all stages: myeloblasts, promyelocytes, myelocytes, metamyelocytes, bands, mature neutrophils
• Basophilia (characteristic and important clue) - an independent adverse prognostic factor
• Eosinophilia often present
• Thrombocytosis frequently seen in early phase

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DIFFERENTIATION: LEUKEMOID REACTION vs. CML

Key Differentiating Test

• Leukemoid reaction: NAP score is high (reactive cells have abundant enzyme activity)
• CML: NAP score is very low (neoplastic cells lack normal alkaline phosphatase)

Treatment of CML (briefly)

• Tyrosine kinase inhibitors (TKIs): Imatinib (first-line), Dasatinib, Nilotinib, Bosutinib
• TKIs have transformed CML from a fatal disease to one with near-normal life expectancy
• Allogeneic stem cell transplantation: reserved for TKI-resistant/intolerant patients, accelerated phase, or blast crisis

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Q3. Hodgkin Lymphoma - Classification, Clinical Features, and Staging

DEFINITION

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EPIDEMIOLOGY AND ETIOLOGY

• Bimodal age distribution: Young adults (15-35 years) and older adults (>55 years)
• Slight male predominance (except nodular sclerosis, which is equal in both sexes)
• EBV association: EBV genome found in RS cells in up to 70% of mixed-cellularity subtype; integration is clonal (infection precedes transformation)
• RS cells originate from germinal center B cells (identical clonal IgV gene rearrangements with somatic hypermutation in each tumor)
• RS cells escape immune surveillance by:
  • Loss of β2-microglobulin → failure to express class I MHC molecules
  • High expression of PD-L1 and PD-L2 (immune checkpoint ligands that suppress T-cell responses)
  • Amplification of chromosome 9p24 (containing PD-L1/PD-L2 genes)

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REED-STERNBERG CELL (Hallmark)

• Large cell (15-45 μm diameter)
• Enormous multilobate or bilobed nucleus
• Exceptionally prominent, large (inclusion-like) acidophilic nucleoli surrounded by a clear halo - gives the classic "owl-eye" appearance
• Abundant, slightly eosinophilic cytoplasm
• Immunophenotype: CD15+, CD30+, CD45-, negative for B-cell (CD20) and T-cell markers
• RS cells typically comprise only a small fraction of the total tumor mass; the bulk consists of reactive inflammatory cells

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CLASSIFICATION (WHO Classification)

A. CLASSIC HODGKIN LYMPHOMA (4 subtypes - share RS cell immunophenotype)

1. Nodular Sclerosis (NS) - Most Common (~65-70%)

• Most common form in developed countries
• Equal frequency in males and females
• Predilection for lower cervical, supraclavicular, and mediastinal lymph nodes (mediastinal involvement very common)
• Peak age: adolescents and young adults
• Morphology: Lacunar cells (RS variant with single multilobate nucleus, pale cytoplasm retracts in formalin - creates "lacunar" space) + thick collagen bands dividing lymphoid tissue into nodules
• Prognosis: Excellent

2. Mixed Cellularity (MC) - Second Most Common (~25%)

• More common in males and in developing countries
• More frequently associated with EBV (up to 70% of cases)
• More likely to be associated with HIV/AIDS
• Often presents with advanced-stage disease and B symptoms
• Morphology: Classic diagnostic "owl-eye" RS cells abundant; background of eosinophils, lymphocytes, plasma cells, and histiocytes
• Prognosis: Good but worse than NS

3. Lymphocyte-Rich (LR) - Rare (~5%)

• Mostly male patients; older adults
• Usually stage I or II at diagnosis; rare B symptoms
• Background: predominantly lymphocytes; RS cells sparse; few eosinophils
• Best prognosis among classic subtypes

4. Lymphocyte Depletion (LD) - Rarest (<1%)

• Predominantly older males; frequently HIV-associated
• Often presents with disseminated disease (Stage III/IV), B symptoms
• Morphology: Relative paucity of lymphocytes; abundant RS cells; diffuse fibrosis or necrosis
• Worst prognosis among all HL subtypes

B. NODULAR LYMPHOCYTE PREDOMINANT HODGKIN LYMPHOMA (NLPHL) (~5%)

• Distinct biology: RS cell variants ("popcorn cells" / lymphocytic and histiocytic [L&H] cells) express germinal center B-cell markers: CD20+, CD45+, BCL6+, CD15-, CD30- (usually)
• Predominantly young males; localized disease
• Indolent course with late relapses; can transform to diffuse large B-cell lymphoma
• Different treatment approach from classic HL

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CLINICAL FEATURES

Lymphadenopathy (Cardinal Feature)

• Painless, non-tender lymphadenopathy - the most common presentation
• Cervical nodes most commonly affected (60-70%), followed by axillary and inguinal
• Mediastinal involvement is particularly common in NS type - may cause SVC obstruction, cough, dyspnea
• Nodes often described as "rubbery" in consistency
• Pel-Ebstein fever - classic but uncommon; cyclical fever alternating with afebrile periods

B Symptoms (Systemic Symptoms)

• Unexplained fever >38°C
• Drenching night sweats
• Unexplained weight loss >10% of body weight in 6 months
• Absence = "A" suffix; Presence = "B" suffix in staging (e.g., Stage IIA, IIB)

Other Symptoms

• Pruritus (generalized, sometimes severe) - may precede other symptoms by months
• Alcohol-induced pain at sites of lymph node involvement (characteristic but uncommon)
• Splenomegaly (in advanced disease)
• Hepatomegaly
• Anemia (normocytic normochromic)
• In advanced stages: fatigue, susceptibility to infections (particularly herpes zoster)

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STAGING (Ann Arbor Classification with Cotswold Modification)

• A = No B symptoms
• B = Presence of fever, night sweats, or >10% weight loss
• E = Extranodal extension from adjacent node
• S = Splenic involvement
• X = Bulky disease (largest diameter ≥10 cm or mediastinal mass >1/3 thoracic diameter)

Staging Notes

• PET-CT has replaced bone marrow biopsy for initial staging
• Stage IV excludes limited extranodal sites (which receive E designation) - Stage IV is for diffuse extranodal disease (bone marrow, liver, lung, bone)
• Bulky disease: Any tumor mass ≥10 cm - treated as advanced disease regardless of stage number

Staging Work-Up

• History (B symptoms), physical examination
• Blood counts, LDH, ESR, albumin, CRP
• CT scan chest/abdomen/pelvis
• PET-CT (now gold standard - superior to CT and gallium scan)
• Bone marrow biopsy (if PET negative and clinically suspected)
• Excisional lymph node biopsy (for histology) - needle biopsy insufficient

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TREATMENT (Brief Overview)

• Combined modality therapy: ABVD chemotherapy (Adriamycin, Bleomycin, Vinblastine, Dacarbazine) × 2-4 cycles + involved-field radiotherapy (IFRT)
• 5-year survival >90-95%

• ABVD × 6-8 cycles ± radiotherapy to residual/bulky sites
• BEACOPP (escalated) in high-risk advanced disease (higher efficacy, more toxicity)
• 5-year disease-free survival ~50-60% in stage IV

• Anti-PD-1 antibodies (pembrolizumab, nivolumab) - highly effective (PD-L1 overexpression makes HL exquisitely sensitive)
• Brentuximab vedotin (anti-CD30 antibody-drug conjugate)
• High-dose chemotherapy + autologous stem cell transplantation

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Q4. Myelodysplastic Syndrome (MDS)

DEFINITION

1. Ineffective hematopoiesis - marrow is hypercellular but blood counts are low
2. Dysplastic morphology in one or more hematopoietic cell lines
3. Peripheral cytopenias (anemia, neutropenia, thrombocytopenia, or combinations)
4. Variable risk of transformation to Acute Myeloid Leukemia (AML) - hence the historical term "preleukemia"

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EPIDEMIOLOGY

• Predominantly a disease of the elderly (median age at diagnosis: 7th-8th decade)
• Slight male predominance
• Incidence increases markedly with age (rare below age 50)

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ETIOLOGY / RISK FACTORS

Primary (de novo) MDS

• Idiopathic - most common
• Likely accumulation of somatic mutations with aging

Secondary (Therapy-Related) MDS - t-MDS

• Alkylating agents (cyclophosphamide, melphalan) - latency 4-6 years; monosomy 5 or 7
• Topoisomerase II inhibitors (etoposide, doxorubicin) - shorter latency 1-3 years; 11q23 translocations
• Radiotherapy
• Benzene and other chemical exposures

Predisposing Factors

• Inherited bone marrow failure syndromes (Fanconi anemia, Diamond-Blackfan anemia)
• Acquired aplastic anemia treated with immunosuppression
• Paroxysmal nocturnal hemoglobinuria (PNH)

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PATHOGENESIS

1. Clonal origin: MDS arises from a single multipotent hematopoietic stem cell that has acquired somatic mutations. All affected cell lines (erythroid, myeloid, megakaryocytic) derive from this abnormal clone.
2. Somatic mutations: Common mutations include:
   • Splicing factor genes: SF3B1 (associated with ring sideroblasts - favorable prognosis), SRSF2, U2AF1
   • Epigenetic regulators: TET2, DNMT3A, IDH1/IDH2, EZH2, ASXL1
   • Transcription factors: RUNX1, ETV6
   • Tumor suppressors: TP53 (associated with del(5q), complex karyotype - poor prognosis)
3. Chromosomal abnormalities: Common cytogenetic changes include:
   • Del(5q) - favorable prognosis; responds to lenalidomide
   • Del(7q)/Monosomy 7 - poor prognosis
   • Del(20q), +8 (trisomy 8)
   • Complex karyotype (≥3 abnormalities) - poor prognosis
4. Ineffective hematopoiesis: Despite marrow hypercellularity, abnormal precursors undergo accelerated apoptosis within the marrow, resulting in peripheral cytopenias. Dysregulated inflammatory signaling (TNF-α, TGF-β) contributes.
5. Progression to AML: Accumulation of additional mutations (especially TP53, FLT3, KRAS, NRAS) drives progression. Risk correlates with blast percentage in marrow.

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WHO CLASSIFICATION (2016/2022)

• Number of dysplastic cell lines (single vs. multilineage)
• Presence of ring sideroblasts
• Percentage of blasts in blood and marrow
• Cytogenetics

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CLINICAL FEATURES

Symptoms

• Often discovered incidentally on routine blood count in an asymptomatic patient
• Symptoms of anemia: Fatigue, pallor, dyspnea, weakness (most common presenting complaint)
• Symptoms of neutropenia: Recurrent infections (bacterial, fungal)
• Symptoms of thrombocytopenia: Easy bruising, petechiae, mucosal bleeding, epistaxis
• Some patients are transfusion-dependent from diagnosis
• Splenomegaly may be present but is not a dominant feature

Physical Examination

• Pallor
• Petechiae/purpura, ecchymoses
• Signs of infection
• Mild splenomegaly in some cases

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LABORATORY FINDINGS

Peripheral Blood

• Cytopenias (one or more cell lines): anemia most common; pancytopenia in multilineage disease
• MCV: Usually elevated (macrocytic anemia) or normocytic; occasionally microcytic
• Dysplastic red cells: Oval macrocytes, hypochromic cells, dacryocytes (teardrop cells)
• Dysplastic neutrophils: Hyposegmented (pseudo-Pelger-Huet anomaly), hypogranular cytoplasm
• Dysplastic platelets: Giant platelets, hypogranular platelets
• Monocytosis (in CMML variant)
• Blasts may be present in peripheral blood (in MDS-EB)
• Reticulocyte count: Low (ineffective erythropoiesis)

Bone Marrow (Mandatory for Diagnosis)

• Hypercellular marrow (paradoxical given cytopenias)
• Dysplasia in one or more cell lines:
  • Erythroid dysplasia: Megaloblastoid changes, nuclear budding, multinuclearity, ring sideroblasts (iron-laden mitochondria around nucleus - Prussian blue stain)
  • Granulocytic dysplasia: Hypogranular granules, pseudo-Pelger-Huet cells, hypersegmentation
  • Megakaryocytic dysplasia: Micromegakaryocytes, hypolobated/monolobated nuclei
• Blast percentage (myeloblasts) is critical for classification and prognosis
• Ring sideroblasts: ≥15% of erythroid precursors have iron encircling ≥1/3 of nucleus (Prussian blue stain on BM aspirate)

Other Tests

• Cytogenetics (karyotype): Essential; identifies prognostic chromosomal abnormalities
• FISH and molecular studies: Detection of SF3B1, TET2, TP53, etc.
• Iron studies (serum ferritin often elevated - iron loading from transfusions)
• Erythropoietin level (guides EPO therapy decision)

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PROGNOSTIC SCORING: IPSS-R

• Bone marrow blast percentage
• Cytogenetic risk group
• Hemoglobin level
• Platelet count
• Absolute neutrophil count

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TREATMENT

Supportive Care (All patients)

• Red cell transfusions: For symptomatic anemia (target Hb ~8-10 g/dL)
• Platelet transfusions: For clinically significant bleeding
• Iron chelation therapy: Desferrioxamine or deferasirox for transfusion-dependent iron overload (ferritin >1000 μg/L)
• G-CSF/GM-CSF: For severe neutropenia with recurrent infections (short-term)
• Infection management: Prompt antimicrobials; antifungal prophylaxis in neutropenic patients

Disease-Modifying Therapy

• Erythropoiesis-stimulating agents (ESA): Erythropoietin (EPO) or darbepoetin alpha - first-line for anemia in low-risk MDS with low EPO level (<200 IU/L); response rate ~40-60%
• Lenalidomide: Drug of choice for MDS with isolated del(5q); achieves transfusion independence in ~70% and cytogenetic remission in ~50%
• Luspatercept: Transforming growth factor-β (TGF-β) pathway inhibitor; approved for transfusion-dependent anemia in MDS-RS
• Immunosuppressive therapy (ATG + cyclosporine): For younger patients with hypocellular MDS or those with HLA-DR15 (who may respond like aplastic anemia)
• Azacitidine (low dose)/Decitabine: Hypomethylating agents may be used in some intermediate-risk patients

• Hypomethylating agents (HMA): Azacitidine (first-line) or Decitabine; demethylate silenced tumor suppressor genes; prolong survival and delay AML transformation vs. supportive care; NOT curative
• Intensive chemotherapy (AML-like induction): May be considered in younger fit patients as bridge to transplant
• Allogeneic hematopoietic stem cell transplantation (allo-HSCT): The ONLY potentially curative treatment for MDS; reserved for younger patients (<65-70 years) in good performance status with suitable donor; reduced-intensity conditioning extends eligibility to older patients; best results in lower blast percentage and earlier disease course

Newer/Emerging Therapies

• Venetoclax (BCL-2 inhibitor) + HMA: Being studied in MDS
• Enasidenib/Enasidenib (IDH2 inhibitor): For IDH2-mutated MDS
• Rigosertib, CPX-351 under investigation

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PROGNOSIS

• Highly variable based on IPSS-R risk category
• Very Low risk: Median survival ~9 years; very low AML transformation risk
• Very High risk: Median survival ~0.8 years; high AML transformation rate
• Patients who progress to AML ("secondary AML") have a particularly poor prognosis compared to de novo AML
• Long-term complications of transfusion therapy: iron overload causing hepatic, cardiac, and endocrine damage

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KEY EXAM POINTS SUMMARY

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