The 20% blast threshold in the bone marrow (or peripheral blood) is the critical diagnostic criterion that distinguishes Acute Myelogenous Leukemia (AML) from other myeloid neoplasms.

• a) Chronic Lymphocytic Leukemia (CLL): This is characterized by an accumulation of mature-looking lymphocytes, not blasts.

• b) Myelodysplastic Syndromes (MDS): By definition, MDS has less than 20% blasts in the bone marrow. Once the blast count reaches 20% or more, the diagnosis is changed to AML.

• c) Polycythemia Vera (PV): This is a myeloproliferative neoplasm characterized by an overproduction of red blood cells and other myeloid elements, without a significant increase in blasts.

• Reed-Sternberg cells and their variants are the pathognomonic, malignant cells of Hodgkin lymphoma. Their presence is essential for the diagnosis.

The other options are incorrect:

• a) AML: This is a malignancy of myeloid blasts. Reed-Sternberg cells are not present.

• b) CLL: This is a malignancy of mature B lymphocytes. Reed-Sternberg cells are not a feature.

• d) CML: This is a myeloproliferative neoplasm. Reed-Sternberg cells are not associated with CML.

• Auer rods are needle-shaped aggregates of primary granules that are pathognomonic for a neoplasm of myeloid origin.

• Their presence in blasts is a definitive morphological criterion for a diagnosis of Acute Myeloid Leukemia (AML), as they are not seen in lymphoblasts.

• They can occasionally be seen in high-grade Myelodysplastic Syndromes (MDS), but in that context, they still indicate a myeloid neoplasm and their presence can change the classification to a higher-risk subtype.

The other options are incorrect because:

• a) ALL: This is a malignancy of lymphoblasts, which do not contain the primary granules necessary to form Auer rods.

• c) CLL: This is a malignancy of mature lymphocytes.

• d) CML: While CML is a myeloid neoplasm, Auer rods are not a feature of its chronic phase. Their appearance would signal a transformation to an accelerated or blast phase, which is essentially an acute leukemia (myeloid blast crisis).

• By definition, CLL is a malignancy characterized by the progressive accumulation of monoclonal, immunologically incompetent, mature-looking B lymphocytes in the blood, bone marrow, and lymphoid tissues.

Let’s review the other options:

• a) Malignancy of the thymus: This describes T-cell acute lymphoblastic leukemia/lymphoma or thymomas, not CLL, which is a B-cell disease.

• b) Accumulation of prolymphocytes: This describes B-cell prolymphocytic leukemia (PLL), a more aggressive disease distinct from classic CLL. While CLL cells can sometimes transform into a prolymphocytoid variant, an accumulation of prolymphocytes is not the defining feature.

• d) Accumulation of hairy cells in the spleen: This is the hallmark of Hairy Cell Leukemia (HCL), a different B-cell malignancy.

• The normal M:E ratio ranges from 2:1 to 4:1. An M:E ratio of 6:1 is elevated, indicating a disproportionate increase in the myeloid (granulocytic) cell line compared to the erythroid cell line.

• Granulocytic hyperplasia means an excessive proliferation of the myeloid series (neutrophils, eosinophils, basophils and their precursors), which directly causes this high ratio.

Let’s review the other options:

• a) Lymphoid hyperplasia: An increase in lymphocytes would not directly affect the M:E ratio, as the M:E ratio specifically compares the myeloid and erythroid lineages. Lymphoid cells are considered separately.

• c) Normoblastic hyperplasia: This refers to an increase in erythroid precursors, which would cause the M:E ratio to be decreased or low, not elevated.

• d) Myeloid hypoplasia: This means a decrease in myeloid cells, which would also cause a low M:E ratio.

• The BCR-ABL fusion gene and its transcript are the molecular drivers of CML. Quantitative polymerase chain reaction (qPCR) is the gold-standard method for monitoring disease burden and response to tyrosine kinase inhibitor (TKI) therapy. It provides a highly sensitive and specific measurement of the level of minimal residual disease.

The other options are incorrect:

• a) Hemoglobin level: This is a general measure of anemia and is not specific for monitoring CML disease activity.

• b) LDH: While LDH can be elevated in CML and other hematologic malignancies due to cell turnover, it is a non-specific marker and not used for precise monitoring of treatment response.

• d) Serum ferritin: This is a measure of iron stores and is not used to monitor CML.

• The Tartrate-resistant acid phosphatase (TRAP) test is a classic cytochemical stain that is strongly positive in the vast majority of Hairy Cell Leukemia (HCL) cases. This characteristic helped define the disease historically and is still a useful diagnostic tool, though it has been largely supplemented by more specific immunophenotyping (e.g., CD103, CD25).

Let’s review the other options:

• a) Peroxidase test: This is used to identify the primary granules of cells in the myeloid lineage (e.g., in AML). Hairy cells are of B-cell lineage and are peroxidase-negative.

• c) Sudan black B test: This is another stain for myeloid granules and is positive in most AML cases. Hairy cells are Sudan black B-negative.

• d) Periodic acid-Schiff (PAS) test: This stain detects glycogen and glycoproteins and can be positive in some lymphoblastic leukemias (ALL) and erythroid precursors, but it is not characteristic of HCL.

The Philadelphia chromosome (t(9;22)(q34;q11)) results in the BCR-ABL fusion gene, which produces a constitutively active tyrosine kinase. This is a hallmark of CML and is present in >90% of cases.

• AML-M5, or Acute Monocytic Leukemia, is characterized by the proliferation of monoblasts and promonocytes.

• These leukemic cells have a tendency to infiltrate tissues, leading to distinctive clinical features such as gum hypertrophy (overgrowth), skin infiltration (leukemia cutis), and central nervous system involvement.

The other options are incorrect:

• b) AML-M3 (Acute Promyelocytic Leukemia): Presents with a coagulopathy (DIC), not gum hypertrophy.

• c) ALL (Acute Lymphoblastic Leukemia): May present with bone pain and lymphadenopathy, but gum hypertrophy is not a feature.

• d) CLL (Chronic Lymphocytic Leukemia): Presents with lymphocytosis and lymphadenopathy; it is a disease of mature lymphocytes, not monoblasts.

• Basophilia is a hallmark of CML and is part of the neoplastic proliferation of the myeloid line. It is a very specific finding.

• A leukemoid reaction (a reactive, non-malignant increase in WBCs) typically shows a spectrum of mature neutrophils and earlier forms but does not typically feature basophilia.

The other options are not reliable distinguishers:

• a) High WBC count: Both CML and a leukemoid reaction can have very high WBC counts.

• c) Elevated ESR: This is a non-specific marker of inflammation and can be elevated in both conditions.

• d) Increased platelets: Platelet counts can be variable in both CML (often elevated) and leukemoid reactions (usually normal).

• Multiple Myeloma is defined by a neoplastic proliferation of plasma cells in the bone marrow. The finding of “sheets” or large clusters of these cells (often comprising more than 10% of marrow cellularity, and frequently much higher) is a key diagnostic feature.

• a) Waldenström Macroglobulinemia: This is characterized by a lymphoplasmacytic infiltration in the bone marrow (a mix of small lymphocytes and plasma cells), not sheets of immature plasma cells.

• c) Hairy Cell Leukemia: The bone marrow shows diffuse infiltration by “hairy cells” (a type of B-cell) and is often difficult to aspirate (“dry tap”). Plasma cells are not the feature.

• d) Sézary Syndrome: This is a T-cell lymphoma/leukemia primarily affecting the skin and blood, not the bone marrow with plasma cells.

May-Hegglin Anomaly is a rare, inherited autosomal dominant disorder caused by a mutation in the MYH9 gene. Its classic triad of findings includes:

1. Giant platelets (thrombocytopenia may also be present)

2. Döhle body-like inclusions in the cytoplasm of neutrophils and other granulocytes. These are aggregates of non-functioning ribosomal RNA.

3. Variable thrombocytopenia.

Let’s review why the other options are incorrect:

• b) Chédiak-Higashi Syndrome: Characterized by giant granules in leukocytes, not Döhle bodies or giant platelets.

• c) Alder-Reilly Anomaly: Characterized by coarse, dark azurophilic granules in leukocytes due to mucopolysaccharidoses.

• d) Pelger-Huët Anomaly: Characterized by neutrophils with bilobed (“pince-nez”) nuclei and coarse, clumped chromatin. It does not involve platelet size or Döhle bodies.

• CD20 is a pan-B-cell marker and is strongly expressed on the surface of the neoplastic B-cells in Chronic Lymphocytic Leukemia (CLL).

Let’s review why the other options are incorrect:

• b) CD3: This is a pan-T-cell marker. CLL is a B-cell malignancy, so it is CD3-negative.

• c) CD34: This is a marker for hematopoietic stem cells and progenitor cells (blasts). The malignant cells in CLL are mature lymphocytes, not blasts, so they are CD34-negative.

• d) CD13: This is a myeloid marker. CLL cells, being of lymphoid lineage, are CD13-negative.

• Smudge cells (or basket cells) are a classic morphological finding in CLL. They are fragile, mature lymphocytes that rupture during the mechanical stress of slide preparation, leaving a smudged nuclear remnant. The neoplastic lymphocytes in CLL are particularly fragile, leading to a high number of these cells on the smear.

The other options are incorrect because:

• a) AML & c) ALL: These are acute leukemias involving blasts, which are generally more robust and do not typically form smudge cells.

• d) Hodgkin lymphoma: This lymphoma primarily involves lymph nodes, and Reed-Sternberg cells are its characteristic cellular finding, not smudge cells. Peripheral blood involvement is rare.

• Essential Thrombocythemia (ET) is a classic myeloproliferative neoplasm (MPN) characterized by the sustained overproduction of platelets.

Let’s review the other options:

• a) Refractory Anemia: This is a subtype of Myelodysplastic Syndrome (MDS), which is a disorder of ineffective hematopoiesis, not a proliferative one.

• c) Secondary Erythrocytosis: This is a reactive (non-neoplastic) increase in red blood cells due to an underlying cause like hypoxia, not a primary bone marrow malignancy.

• d) Chronic Myelomonocytic Leukemia (CMML): This is classified as a Myelodysplastic/Myeloproliferative Neoplasm (MDS/MPN), as it has features of both dysplasia (MDS) and proliferation (MPN). It is not a pure MPN.

• The “starry sky” appearance is a classic histological pattern characterized by a background of dark blue, monotonous lymphomatous cells (the “night sky”) scattered with numerous pale-staining, tangible-body macrophages that have ingested apoptotic debris (the “stars”). This is a hallmark of the high proliferation rate and apoptosis seen in Burkitt lymphoma.

The other options are incorrect:

• a) Hodgkin lymphoma: The classic finding is Reed-Sternberg cells in an inflammatory background.

• c) Follicular lymphoma: The hallmark is a nodular or follicular growth pattern.

• d) Mantle cell lymphoma: The pattern can be diffuse, nodular, or mantle zone, but not a “starry sky” pattern.

• Multiple myeloma is a plasma cell malignancy that primarily resides in the bone marrow. These cells produce factors that activate osteoclasts, leading to lytic (punched-out) bone lesions. This bone destruction, in turn, causes hypercalcemia. Bone pain and pathologic fractures are common presenting symptoms.

The other options are not characteristic of multiple myeloma:

• b) Elevated RBC mass: This is the hallmark of polycythemia vera. Multiple myeloma typically causes anemia, not erythrocytosis.

• c) Elevated WBC count: This is not a typical feature. The WBC count is usually normal or low.

• d) Increased platelet count: This is not a feature; thrombocytopenia is more common due to bone marrow infiltration.

Hairy Cell Leukemia (HCL) has a very characteristic immunophenotype. The malignant B-cells are positive for CD11c, CD19, CD20, CD22, CD25, CD103, and CD123.

• a) CD5: This is a hallmark of Chronic Lymphocytic Leukemia (CLL/SLL) and Mantle Cell Lymphoma, not HCL.

• b) CD10: This is often expressed in Follicular Lymphoma and Burkitt Lymphoma, not typically in HCL.

• d) CD3: This is a T-cell marker. HCL is a B-cell malignancy, so it would be negative for CD3.

• Polycythemia vera (PV) is a classic myeloproliferative neoplasm (MPN). It is characterized by the overproduction of red blood cells, and often white blood cells and platelets, from a clonal hematopoietic stem cell.

The other options are all types of lymphoma, which are malignancies of the lymphoid system, not the myeloid system:

• a) Follicular lymphoma: A B-cell non-Hodgkin lymphoma.

• c) Burkitt lymphoma: An aggressive B-cell non-Hodgkin lymphoma.

• d) Hodgkin lymphoma: A distinct type of lymphoma defined by the presence of Reed-Sternberg cells.

• Follicular lymphoma is an indolent B-cell non-Hodgkin lymphoma that classically presents with widespread, painless lymphadenopathy.

• The vast majority of cases (about 85-90%) are associated with the t(14;18)(q32;q21) translocation. This translocation places the BCL2 gene from chromosome 18 under the control of the immunoglobulin heavy chain enhancer on chromosome 14, leading to overexpression of the BCL-2 protein. This protein inhibits apoptosis (programmed cell death), allowing the malignant cells to survive.

The other options are incorrect:

• a) Burkitt lymphoma: Is associated with the MYC oncogene translocation, t(8;14), not BCL2.

• c) Hodgkin lymphoma: Does not have a characteristic BCL2 translocation.

• d) T-cell lymphoma: Is derived from T-cells, and BCL2 translocations are not a defining feature.

• Multiple myeloma is defined by the neoplastic proliferation of plasma cells in the bone marrow. These malignant plasma cells produce a monoclonal immunoglobulin, known as an M protein (or M spike), which can be detected in the blood or urine.

The other options are incorrect:

• b) CLL: This is a malignancy of mature B lymphocytes, not plasma cells. While some patients can have a small monoclonal protein, it is not the defining feature.

• c) ALL: This is a malignancy of lymphoblasts (immature lymphocytes). It does not involve mature plasma cells or M protein production.

• d) CML: This is a malignancy of the myeloid lineage (granulocytes) and does not involve plasma cells.

• CD138 is a highly specific marker for terminally differentiated B-cells, namely plasma cells. It is a cornerstone immunophenotypic marker for identifying and diagnosing Multiple Myeloma.

Let’s review why the other options are incorrect:

• a) CD7: This is a T-cell and NK-cell marker. Plasma cells are of B-cell lineage and do not express CD7.

• b) CD19: This is a pan-B-cell marker expressed on normal B-cells and plasma cells. However, neoplastic plasma cells in Multiple Myeloma frequently lose CD19, making its absence a common diagnostic finding.

• d) CD3: This is a pan-T-cell marker. Plasma cells are not of T-cell lineage and are CD3-negative.

• Tear-drop cells (dacrocytes) are a classic morphological finding in myelofibrosis. They are formed when red blood cells are squeezed out of a fibrotic bone marrow that has lost its normal architecture and plasticity. This finding is often part of a “leukoerythroblastic” picture (the presence of immature myeloid and erythroid precursors in the blood).

The other options are incorrect:

• a) AML, c) CLL, d) ALL: While tear-drop cells can be seen in various conditions involving bone marrow infiltration (including advanced cancers), they are not a characteristic or defining feature of these leukemias. Their presence is most specifically and commonly associated with myelofibrosis.

• Acute Lymphoblastic Leukemia (ALL) is the most common childhood cancer, accounting for about 75-80% of childhood leukemias. The presence of lymphoblasts in the peripheral blood is a classic presentation.

• a) AML (Acute Myeloid Leukemia): This is the second most common childhood leukemia but is far less common than ALL. The blasts would be myeloblasts, not lymphoblasts.

• b) CLL (Chronic Lymphocytic Leukemia): This is a disease of adults and is exceptionally rare in children.

• d) CML (Chronic Myelogenous Leukemia): This is also very rare in children and presents with a full spectrum of myeloid cells (myelocytes, metamyelocytes) in the peripheral blood, not primarily lymphoblasts.

• Acute Lymphocytic Leukemia (ALL) accounts for approximately 75-80% of all childhood leukemia cases, making it by far the most common type.

• a) Acute Granulocytic Leukemia and c) Acute Monocytic Leukemia are both subtypes of Acute Myeloid Leukemia (AML). AML is the second most common childhood leukemia but is far less common than ALL, representing about 15-20% of cases.

• d) Chronic Granulocytic Leukemia (CGL/CML): Chronic leukemias are very rare in children.

• The JAK2 V617F mutation is found in over 95% of patients with Polycythemia Vera (PV). It is a cornerstone diagnostic criterion and drives the constitutive activation of the JAK-STAT signaling pathway, leading to erythrocytosis and overproduction of other blood cells.

The other mutations are associated with different hematologic malignancies:

• b) BCR-ABL: Associated with Chronic Myelogenous Leukemia (CML).

• c) PML-RARA: Associated with Acute Promyelocytic Leukemia (APL).

• d) MYC: Associated with Burkitt Lymphoma.

• Bimodal age distribution is a classic epidemiological feature of Hodgkin Lymphoma, with incidence peaks in young adults (around ages 15-35) and again in older adults (over age 55).

Let’s review why the other options are incorrect:

• • a) High incidence of peripheral blood infiltration → Rare in HL; more typical of leukemias.

  • b) Unpredictable lymph node involvement → HL spreads predictably, usually contiguously.

  • d) Uniformly fatal outcome → HL is highly curable, especially in early stages.

• Essential Thrombocythemia (ET) is defined by a sustained, significant increase in platelet count (thrombocytosis), typically > 450,000/µL and often much higher.

The other options are not typical of ET:

• b) Decreased platelet count (thrombocytopenia): This is the opposite of what defines ET.

• c) Increased blasts: The presence of increased blasts in the blood or marrow is not a feature of ET and would suggest progression to a more aggressive disease like AML.

• d) Increased RBC mass: This is the hallmark of Polycythemia Vera (PV), not ET.

• Pelger-Huët Anomaly is a benign, inherited condition characterized by granulocyte hyposegmentation. The nuclei of neutrophils are predominantly bilobed (resembling pince-nez spectacles) or even unsegmented (dumbbell-shaped), with abnormally coarse, clumped chromatin.

Let’s review the other options:

• a) May-Hegglin Anomaly: Associated with giant platelets and Döhle bodies, not nuclear hyposegmentation.

• b) Chédiak-Higashi Syndrome: Associated with giant granules in leukocytes, not nuclear hyposegmentation.

• c) Alder-Reilly Anomaly: Associated with coarse, dark azurophilic granules in leukocytes, not nuclear hyposegmentation.

• The fundamental diagnostic feature of Polycythemia Vera (PV) is an absolute increase in red cell mass, which is reflected in an elevated hematocrit. This is the primary, defining characteristic of the disease.

The other options are incorrect:

• a) Decreased red cell mass: This is the opposite of what defines PV; it would indicate anemia.

• c) Increased blasts in blood: This is not characteristic of the chronic phase of PV. An increase in blasts would suggest progression to a more aggressive phase like myelofibrosis or acute leukemia.

• d) Increased lymphocytes: This is not a feature of PV, which is a disorder of the myeloid lineage (red cells, granulocytes, platelets). Lymphocytosis suggests a lymphoid disorder.

The World Health Organization (WHO) classification has a specific category for overlap syndromes that have features of both myelodysplastic syndromes (MDS) and myeloproliferative neoplasms (MPN). This category is called “Myelodysplastic/Myeloproliferative Neoplasms (MDS/MPN),” and Juvenile Myelomonocytic Leukemia (JMML) is a classic entity within this group.

The other options:

• a) Acute Myelomonocytic Leukemia (AMML): This is a subtype of Acute Myeloid Leukemia (AML), not MDS or MDS/MPN.

• b) Chronic Myelogenous Leukemia (CML): This is classified as a classic Myeloproliferative Neoplasm (MPN), not an MDS/MPN overlap syndrome.

• d) Refractory Anemia with Excess Blasts (RAEB): This is a subtype of Myelodysplastic Syndromes (MDS), not the MDS/MPN overlap category.

• Megaloblastoid erythropoiesis refers to abnormal, dysplastic red blood cell precursors in the bone marrow that resemble megaloblasts (seen in B12/folate deficiency) but without the vitamin deficiency. It is a hallmark of dyserythropoiesis in MDS.

• a) Persistently increased M:E ratio: This is not typical of MDS. While cellularity can vary, dyserythropoiesis often leads to ineffective erythropoiesis, and the M:E ratio may be normal or even decreased.

• b) Marked thrombocytosis: This is incorrect. MDS is characterized by cytopenias, including thrombocytopenia. Marked thrombocytosis is a feature of myeloproliferative neoplasms like Essential Thrombocythemia.

• d) Decreased ferritin levels: Ferritin is an acute phase reactant and is usually normal or increased in MDS due to anemia and frequent red blood cell transfusions (leading to iron overload).

• Rouleaux formation (red blood cells stacking like coins) occurs when there is an increase in plasma proteins, particularly fibrinogen or immunoglobulins.

• Multiple myeloma is characterized by the overproduction of a monoclonal immunoglobulin (M-protein), which significantly increases the protein concentration in the blood, leading to prominent rouleaux formation. This is a classic laboratory finding.

The other options are incorrect:

• a) CML: Does not typically cause a paraproteinemia and is not associated with significant rouleaux.

• c) AML: Is not associated with paraproteinemia or rouleaux formation.

• d) Hodgkin lymphoma: Does not produce a monoclonal paraprotein; rouleaux is not a characteristic finding.

• CLL is the most common leukemia in adults, particularly in Western countries.

• It is a B-cell malignancy characterized by accumulation of small, mature-appearing lymphocytes in the blood, bone marrow, and lymphoid tissues.

• Incidence increases with age, typically presenting in adults >60 years.

Other options:

• ALL → Most common in children, rare in adults.

• AML → Less common than CLL in adults; median age ~65 years.

• CML → Accounts for fewer adult leukemias; characterized by BCR-ABL1 fusion (Philadelphia chromosome).

• Epstein-Barr Virus (EBV) is strongly associated with Burkitt lymphoma, particularly the endemic (African) form, where it is found in nearly all cases. The virus is thought to contribute to the pathogenesis by causing B-cell proliferation, which increases the chance of the MYC translocation occurring.

The other options are incorrect:

• a) CMV (Cytomegalovirus): Not associated with Burkitt lymphoma.

• c) HPV (Human Papillomavirus): Associated with cervical and other anogenital cancers, not Burkitt lymphoma.

• d) HIV (Human Immunodeficiency Virus): HIV is associated with an increased risk of developing Burkitt lymphoma (and other lymphomas) due to immunosuppression, but it is not the direct oncogenic driver like EBV is in the endemic form.

• The Philadelphia chromosome, resulting from the t(9;22)(q34;q11.2) translocation, is the defining genetic abnormality of CML. This translocation creates the BCR::ABL1 fusion oncogene, which drives the uncontrolled proliferation of myeloid cells.

The other options are associated with different malignancies:

• b) t(8;14): Associated with Burkitt lymphoma.

• c) t(15;17): Associated with Acute Promyelocytic Leukemia (APL).

• d) t(11;14): Associated with Mantle cell lymphoma.

• The definitive diagnosis of Hodgkin lymphoma requires a tissue biopsy (typically an excisional lymph node biopsy) showing the characteristic Reed-Sternberg cells in an appropriate inflammatory background.

The other options are incorrect or insufficient:

• a) Peripheral smear: This is not diagnostic. While it may show non-specific findings like anemia, it will not show Reed-Sternberg cells.

• c) Flow cytometry of blood: This is not the primary diagnostic tool, as Reed-Sternberg cells are rarely found in the blood and their phenotype can be difficult to detect by standard flow cytometry.

• d) Serum ferritin: This is a non-specific marker of inflammation and iron stores, not a diagnostic test for Hodgkin lymphoma.

• Acute Promyelocytic Leukemia (APL), the M3 subtype of AML, is notoriously associated with a high risk of life-threatening DIC at presentation. The malignant promyelocytes contain numerous primary granules that are intensely procogaulant. Their release into the bloodstream, either spontaneously or due to the initiation of chemotherapy, can trigger widespread coagulation and fibrinolysis, leading to both thrombosis and hemorrhage.

Let’s review the other options:

• a) Acute Lymphoblastic Leukemia (ALL): DIC is not a common presenting feature of ALL.

• c) Acute Monocytic Leukemia: While it can be associated with coagulopathies, the association is not as strong or classic as it is with APL.

• d) Acute Megakaryoblastic Leukemia: This is a rare subtype of AML, but DIC is not its hallmark presenting feature.

Terminal deoxynucleotidyl transferase (TdT) is a DNA polymerase that is a key marker for immature, precursor lymphoid cells (lymphoblasts).

• a) Mature T cells: Mature T cells are TdT-negative. TdT is expressed in the thymus during T-cell development but is lost upon maturation.

• b) Myeloblasts: Myeloblasts, the blasts of acute myeloid leukemia (AML), are typically TdT-negative (though it can be rarely positive in some cases).

• d) Plasma cells: Plasma cells are mature, terminally differentiated B-cells and are TdT-negative.

• Terminal deoxynucleotidyl transferase (TdT) is a DNA polymerase expressed in the nuclei of immature, precursor lymphoid cells (lymphoblasts).

• Its presence is a hallmark of Acute Lymphoblastic Leukemia (ALL), helping to distinguish it from mature lymphoid malignancies and acute myeloid leukemia.

The other options are incorrect:

• a) AML: Myeloblasts are generally TdT-negative (though rare cases may show weak positivity).

• b) CLL: This is a malignancy of mature B lymphocytes, which are TdT-negative.

• d) CML: The chronic phase involves mature myeloid cells, which are TdT-negative.

Chédiak-Higashi syndrome is a rare autosomal recessive disorder caused by a mutation in the LYST gene. This gene provides instructions for a protein involved in regulating the transport (fusion) of lysosomes and other intracellular vesicles. The fundamental problem is a membrane defect of lysosomes and other cytoplasmic granules, which leads to their abnormal fusion and giant granule formation.

Let’s review the other options, which describe different conditions:

• a) Döhle bodies and giant platelets: This is characteristic of May-Hegglin anomaly.

• c) Two-lobed neutrophils: This is the hallmark of Pelger-Huët anomaly.

• d) Mucopolysaccharidosis: This underlies Alder-Reilly anomaly, where partially degraded mucopolysaccharides accumulate and form coarse granules in leukocytes

The JAK2 V617F mutation is a cornerstone molecular marker in the diagnosis of classic Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). It is found in the vast majority (>95%) of patients with Polycythemia Vera (PV). It is also present in approximately 50-60% of patients with Essential Thrombocythemia (ET) and Primary Myelofibrosis (PMF).

Let’s review the other options:

• a) Chronic Myelogenous Leukemia (CML): CML is defined by the Philadelphia chromosome and the *BCR-ABL1* fusion gene, not the JAK2 mutation.

• c) Acute Monocytic Leukemia: This is a subtype of AML and is not characteristically associated with the JAK2 V617F mutation.

• d) Myelodysplastic Syndrome (MDS): While JAK2 mutations can occur rarely in MDS/MPN overlap syndromes, it is not a defining feature of MDS itself.

Children with Down syndrome have a markedly increased risk of developing leukemia, particularly acute megakaryoblastic leukemia (AMKL, or AML-M7). The risk of developing this specific subtype of AML in the first 4 years of life is several hundred times greater than in children without Down syndrome.

• a) CLL: This is a disease of adults and is not associated with Down syndrome.

• c) CML: This is very rare in children and is not specifically associated with Down syndrome.

• d) Hairy cell leukemia: This is also a disease of adults and is not associated with Down syndrome.

This translocation, which forms the *ETV6-RUNX1* fusion gene, is the most common genetic abnormality in childhood B-ALL and is associated with an excellent response to chemotherapy and a very favorable prognosis.

Let’s review the other options, which are all associated with a poor prognosis:

• a) t(9;22) – Philadelphia chromosome: The *BCR-ABL1* fusion defines “Ph+ ALL,” which is a high-risk subtype.

• b) t(4;11): This *KMT2A-AFF1* (formerly *MLL-AF4*) rearrangement is associated with a very poor prognosis, especially in infant ALL.

• c) t(1;19): The *TCF3-PBX1* fusion was historically considered high-risk, but with contemporary intensified chemotherapy, its prognosis has improved to standard or intermediate risk. However, it is still not considered “favorable” like t(12;21).

• Auer rods are pathognomonic for a myeloid lineage and are most characteristically found in Acute Myelogenous Leukemia (AML), specifically in the blast cells.

• a) Chronic Lymphocytic Leukemia (CLL): This is a malignancy of mature lymphocytes. Lymphoid cells do not contain primary granules and therefore cannot form Auer rods.

• c) Hairy Cell Leukemia: This is a subtype of mature B-cell lymphoma/leukemia. As a lymphoid malignancy, it does not feature Auer rods.

• d) Myelodysplastic Syndrome (MDS): While Auer rods can rarely be seen in the specific subtype “MDS with excess blasts-2 (MDS-EB-2),” their presence is far more common and characteristic of AML. The question asks where they are “most likely” present, making AML the best and most definitive answer.

• Hodgkin lymphoma, specifically the nodular sclerosis subtype, has a peak incidence in young adults and frequently presents with a mediastinal mass.

• The diagnosis is confirmed by the identification of characteristic Reed-Sternberg cells on lymph node biopsy.

The other options are incorrect:

• b) Burkitt lymphoma: Presents as an aggressive extranodal mass (e.g., abdomen, jaw) and is characterized by a “starry-sky” pattern, not Reed-Sternberg cells.

• c) Follicular lymphoma: An indolent lymphoma of older adults, typically presenting with widespread painless lymphadenopathy, not a mediastinal mass.

• d) Mantle cell lymphoma: A B-cell lymphoma that typically affects older adults and often involves the lymph nodes and gastrointestinal tract; it does not feature Reed-Sternberg cells.

• Smudge cells (also called basket cells) are fragile lymphocytes that get damaged during slide preparation. They are a classic, hallmark finding in Chronic Lymphocytic Leukemia (CLL) because the neoplastic lymphocytes in CLL are particularly fragile.

• a) Acute Myelogenous Leukemia (AML): Smudge cells are not a characteristic feature of AML.

• b) Chronic Myelogenous Leukemia (CML): While CML is a leukemia, it is a myeloid disorder, and smudge cells are not a typical finding. The characteristic cell in CML is the full spectrum of myeloid precursors.

• d) Infectious Mononucleosis: The characteristic cells in infectious mononucleosis are reactive lymphocytes (atypical lymphocytes), not smudge cells.

• Acute Myelomonocytic Leukemia (AMML, M4 subtype in the FAB classification) is a subtype of AML with both myeloid and monocytic differentiation.

• In the WHO 2016/2022 classification, AMML does not have a defining recurrent cytogenetic abnormality, nor is it therapy-related or primarily associated with myelodysplasia.

• Therefore, it falls under AML, not otherwise specified (NOS).

Other options:

• a) AML with recurrent cytogenetic changes → Examples include t(8;21), inv(16), t(15;17).

• b) AML with myelodysplastic-related changes → Requires history of MDS or MDS-related cytogenetic/morphologic features.

• d) Therapy-related AML → Occurs after chemotherapy or radiation.

• CML has a natural and predictable progression if untreated. It begins in a chronic phase but will inevitably progress through an accelerated phase and then to a blast crisis, which is essentially an acute leukemia (most commonly AML, sometimes ALL).

The other options have a lower risk of transformation:

• b) CLL: Can transform into a more aggressive lymphoma (Richter’s transformation, often to DLBCL) or, less commonly, to prolymphocytic leukemia or ALL, but this is not as predictable or frequent as in CML.

• c) Polycythemia vera & d) Essential thrombocythemia: These are myeloproliferative neoplasms (MPNs) that carry a risk of transforming to acute leukemia (post-MPN AML), but the risk is significantly lower and less predictable than the inevitable transformation seen in untreated CML. The risk is higher in PV than in ET.

• CD103 is a very specific and characteristic marker for Hairy Cell Leukemia (HCL). It is part of the unique immunophenotype that helps distinguish HCL from other B-cell leukemias.

Let’s review the other options:

• a) CD5: This is a hallmark marker for Chronic Lymphocytic Leukemia (CLL/SLL) and Mantle Cell Lymphoma. Hairy cell leukemia is CD5-negative.

• c) CD3: This is a T-cell marker. Hairy cell leukemia is a B-cell malignancy and is CD3-negative.

• d) CD34: This is a stem cell and progenitor cell (blast) marker. The malignant cells in HCL are mature lymphocytes, not blasts, so they are CD34-negative.

• CML typically progresses through three phases: chronic, accelerated, and blast phase (blast crisis).

• Features suggesting blast transformation include:

  • >20% blasts in peripheral blood or bone marrow

  • Basophilia

  • Thrombocytopenia

• The presence of the Philadelphia chromosome (BCR-ABL1 fusion) confirms CML, as opposed to de novo AML.

Other options:

• a) AML → Could have similar blasts, but Philadelphia chromosome is rare in de novo AML.

• c) Primary Myelofibrosis → Shows marrow fibrosis, teardrop cells, not typically 20% blasts with basophilia.

• d) Essential Thrombocythemia → Thrombocytosis, not typically >20% blasts or basophilia.

CML is a myeloproliferative neoplasm characterized by the uncontrolled proliferation of the myeloid cell line. The bone marrow is hypercellular due to a massive increase in granulocytic precursors (myelocytes, metamyelocytes, neutrophils). This marked expansion of the granulocytic series occurs while the erythroid (red blood cell) precursors are relatively less increased or even suppressed, leading to a significantly elevated or high M:E ratio, often exceeding 10:1 or even 20:1 (the normal range is about 2:1 to 4:1).

Other options:

• a) Normal → Seen in normal marrow.

• c) Low → Would suggest erythroid hyperplasia, not CML.

• d) Variable → Not typical; in CML, M:E ratio is consistently high.

• Chronic Granulomatous Disease (CGD) is caused by defects in the NADPH oxidase complex, which is responsible for generating the respiratory burst that produces superoxide and other reactive oxygen species needed to kill certain bacteria and fungi. Neutrophils in CGD can phagocytose bacteria normally, but they cannot kill them due to this defective oxidative burst.

Let’s review the other options:

• a) Chédiak-Higashi Syndrome: This is characterized by defective granule fusion with the phagosome, which impairs the delivery of microbicidal enzymes, but the oxidative burst is intact.

• c) Pelger-Huët Anomaly: This is a benign condition of nuclear hyposegmentation that does not impair neutrophil killing function.

• d) Alder-Reilly Anomaly: This is characterized by the presence of coarse granules but does not impair the cell’s ability to kill bacteria.

• Sézary cells are the characteristic abnormal T-lymphocytes (with cerebriform nuclei) that circulate in the peripheral blood in Sézary syndrome, which is considered the leukemic phase of Cutaneous T-cell Lymphoma (CTCL).

Let’s review the other options:

• a) Reed-Sternberg Cell: This is the pathognomonic cell of Hodgkin Lymphoma, which rarely has a leukemic phase.

• b) Plasmacytoid Lymphocyte: This is a cell type associated with Lymphoplasmacytic Lymphoma/Waldenström Macroglobulinemia, which is a B-cell, not a T-cell, malignancy.

• d) Mantle Cell: This term refers to the neoplastic cells of Mantle Cell Lymphoma, which is a B-cell lymphoma. While it can have a leukemic phase (often with “blastoid” variants), it is not a T-cell lymphoma.

• The t(15;17)(q24;q21) translocation is the genetic hallmark of Acute Promyelocytic Leukemia (APL), which corresponds to the AML-M3 subtype in the older FAB classification. This translocation creates the PML-RARA fusion gene, which is not only diagnostic but also the critical therapeutic target for all-trans retinoic acid (ATRA) therapy.

The other options are associated with different genetic abnormalities:

• a) AML-M2: Often associated with t(8;21).

• c) AML-M5 (Acute Monocytic Leukemia): Can be associated with various abnormalities involving 11q23 (*KMT2A/MLL* rearrangements).

• d) AML-M7 (Acute Megakaryoblastic Leukemia): Associated with Down syndrome in children, but not with t(15;17).

• Burkitt lymphoma is a highly aggressive B-cell non-Hodgkin lymphoma, which is a malignancy of the lymphoid system. It is not a disorder of the myeloid cell lines.

The other three are classic Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs):

• a) Polycythemia vera

• b) Essential thrombocythemia

• c) Primary myelofibrosis

The immunophenotype of CLL/SLL is characteristically CD5+ and CD23+. This combination is very helpful in distinguishing CLL from other B-cell malignancies.

Let’s review the other options:

• a) CD5-/CD23-: This is a common phenotype for many B-cell lymphomas, such as Follicular Lymphoma or Marginal Zone Lymphoma.

• b) CD5-/CD23+: This is not a classic pattern for a common lymphoma.

• c) CD5+/CD23-: This is the classic immunophenotype for Mantle Cell Lymphoma, a key differential diagnosis for CLL.

• The t(11;14)(q13;q32) translocation is the genetic hallmark of Mantle Cell Lymphoma (MCL). This translocation places the CCND1 (cyclin D1) gene from chromosome 11 under the control of the immunoglobulin heavy chain enhancer on chromosome 14, leading to overexpression of cyclin D1 and dysregulation of the cell cycle.

The other options are associated with different translocations:

• a) Burkitt lymphoma: Associated with t(8;14) involving the MYC gene.

• c) Hodgkin lymphoma: Does not have a characteristic recurrent translocation like t(11;14).

• d) Follicular lymphoma: Associated with t(14;18) involving the BCL2 gene.

• The t(8;14) is the classic and most common cytogenetic abnormality in Burkitt Lymphoma. This translocation places the c-MYC oncogene from chromosome 8 under the control of the powerful immunoglobulin heavy chain enhancer on chromosome 14, leading to uncontrolled cell proliferation.

• b) Acute Promyelocytic Leukemia: This is associated with t(15;17), which involves the PML and RARA genes.

• c) Follicular Lymphoma: This is most commonly associated with t(14;18), which involves the BCL-2 and IGH genes.

• d) Multiple Myeloma: Has a variety of cytogenetic abnormalities, but t(8;14) is not characteristic. Common translocations often involve the IGH locus on chromosome 14 with partners like CCND1 (11q13), FGFR3 (4p16), or MAF (16q23).

• Niemann-Pick Disease is a lysosomal storage disorder caused by a deficiency of the enzyme sphingomyelinase. This leads to the accumulation of its substrate, sphingomyelin, within the lysosomes of macrophages. These lipid-laden macrophages appear as large, pale, vacuolated “foam cells” in the bone marrow and other organs.

Let’s review the other options:

• a) Gaucher Disease: This is caused by a deficiency of glucocerebrosidase, leading to the accumulation of glucocerebroside. The resulting macrophages are called Gaucher cells, which have a characteristic “wrinkled tissue paper” or fibrillary cytoplasm, not a vacuolated foam cell appearance.

• b) Multiple Myeloma: The bone marrow shows an infiltration of plasma cells, not foam cells.

• d) DiGuglielmo Disease: This is an old term for acute erythroid leukemia, characterized by a proliferation of immature erythroid precursors, not foam cells.