## Correct Answer: A. t(15;17) The "faggot cell" (also called Auer rod or abnormal promyelocyte) is the pathognomonic morphological hallmark of **acute promyelocytic leukemia (APL)**, a subtype of acute myeloid leukemia (AML-M3 by FAB classification). The translocation **t(15;17)** is the defining cytogenetic abnormality in APL, resulting in the PML-RARA fusion gene. This fusion produces an abnormal retinoic acid receptor that blocks normal myeloid differentiation at the promyelocyte stage. The abnormal promyelocytes are packed with Auer rods (bundles of azurophilic granules), which appear as "faggot cells" on peripheral smear—a term reflecting their bundle-like appearance. APL is clinically significant because it presents with severe bleeding due to disseminated intravascular coagulation (DIC) from release of procoagulant substances from abnormal promyelocytes. The presence of t(15;17) is crucial for diagnosis and treatment selection, as APL responds dramatically to all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), which are now standard of care in India and globally. This translocation is found in >95% of APL cases, making it virtually diagnostic. ## Why the other options are wrong **B. t(14;18)** — This translocation is associated with **follicular lymphoma** (BCL2-IGH fusion), not acute leukemia. It produces a lymphoid malignancy with t(14;18) seen on cytogenetics or FISH, not a myeloid disorder. The morphology would show lymphoid cells, not abnormal promyelocytes with Auer rods. This is a common NBE trap pairing different hematologic malignancies. **C. t(8;21)** — This translocation defines **AML with t(8;21)** (AML-M2, acute myeloblastic leukemia with maturation), producing the RUNX1-RUNX1T1 fusion. While it is an AML subtype, it does NOT produce faggot cells or Auer rods as a characteristic finding. The morphology shows myeloblasts with Auer rods occasionally, but the distinctive abnormal promyelocytes with bundled Auer rods (faggot cells) are specific to APL. **D. t(11;14)** — This translocation is associated with **mantle cell lymphoma** (CCND1-IGH fusion), a B-cell lymphoma, not acute myeloid leukemia. It would present with lymphoid morphology and lymphadenopathy, not bleeding from DIC or abnormal promyelocytes. The presence of faggot cells and acute bleeding presentation rules out this lymphoid malignancy entirely. ## High-Yield Facts - **t(15;17)** is the defining translocation of acute promyelocytic leukemia (APL/AML-M3), found in >95% of cases. - **Faggot cells** (abnormal promyelocytes packed with Auer rods) are pathognomonic for APL and appear as bundle-like structures on peripheral smear. - APL presents with **severe bleeding and DIC** due to release of procoagulant substances from abnormal promyelocytes; this is a medical emergency. - **ATRA (all-trans retinoic acid) and arsenic trioxide (ATO)** are the standard of care for APL in India, with cure rates >90% in modern protocols. - The PML-RARA fusion protein blocks myeloid differentiation; ATRA and ATO induce differentiation and degradation of the fusion protein, respectively. ## Mnemonics **APL = t(15;17) = Faggot cells + DIC** When you see **abnormal promyelocytes with Auer rods (faggot cells) + bleeding/DIC**, think **t(15;17) APL**. The PML gene is on chromosome 15, RARA on 17—remember '15-17' as the APL code. **AML translocations by morphology** **t(8;21)** = AML-M2 (myeloblasts with Auer rods); **t(15;17)** = AML-M3 (abnormal promyelocytes with BUNDLED Auer rods = faggot cells); **t(9;11)** = AML-M5 (monocytic). The morphology is the key discriminator. ## NBE Trap NBE pairs different AML translocations (t(8;21), t(15;17)) to test whether students can distinguish morphology: t(8;21) shows myeloblasts, while t(15;17) specifically shows abnormal promyelocytes with bundled Auer rods (faggot cells). The bleeding presentation is a red herring if students don't link it to DIC from APL. ## Clinical Pearl In Indian practice, APL is a medical emergency—any patient presenting with acute bleeding and abnormal promyelocytes on smear should be started on ATRA immediately (even before cytogenetics confirm t(15;17)) because DIC can be rapidly fatal. Modern APL protocols in India (AIIMS, TATA Memorial) achieve >90% cure rates with ATRA + ATO, making early recognition life-saving. _Reference: Robbins Ch. 13 (Hematopoietic and Lymphoid Systems); Harrison Ch. 110 (Acute Myeloid Leukemia)_
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