A 25-year-old male presented with low hemoglobin, platelet count of 25,000/mL, gum bleeding, and raised PT & aPTT. The image of his peripheral smear is given below. What is the likely diagnosis?

Explanation

## Correct Answer: D. AML with t(15;17) The clinical presentation of severe thrombocytopenia (25,000/mL), gum bleeding, coagulopathy (raised PT & aPTT), and anemia in a young adult with abnormal cells on peripheral smear is pathognomonic for **acute promyelocytic leukemia (APL)**, which is AML with t(15;17). This translocation fuses the PML gene on chromosome 15 with the RARA (retinoic acid receptor alpha) gene on chromosome 17, creating the PML-RARA fusion protein. APL is uniquely characterized by severe **disseminated intravascular coagulation (DIC)** due to release of procoagulant substances (tissue factor, cancer procoagulant) from abnormal promyelocytes. The peripheral smear typically shows abnormal promyelocytes with abundant Auer rods (often multiple, forming "faggot cells"). The combination of thrombocytopenia + bleeding + coagulopathy (PT/aPTT elevation) is the hallmark of APL-associated DIC. APL is the most curable AML subtype (>90% remission with all-trans retinoic acid [ATRA] + arsenic trioxide in Indian centers), making early recognition critical. The t(15;17) is the defining cytogenetic abnormality and is essential for diagnosis per WHO classification. ## Why the other options are wrong **A. AML with t(11;22)** — t(11;22) is extremely rare in AML and is more commonly associated with Ewing sarcoma and other sarcomas, not hematologic malignancies. This translocation does not produce the characteristic DIC and coagulopathy seen in this case. The clinical presentation of severe coagulopathy with thrombocytopenia is not typical of t(11;22) AML. **B. AML with t(8;21)** — t(8;21) produces the RUNX1-RUNX1T1 fusion and is associated with AML-M2 (AML with maturation). While it is a favorable-risk AML, it does NOT cause severe DIC or the marked coagulopathy seen here. Patients with t(8;21) typically present with higher platelet counts and do not have the characteristic bleeding diathesis from DIC. **C. AML with inv(16)** — inv(16) produces CBFB-MYH11 fusion and is associated with AML-M4Eo (acute myelomonocytic leukemia with eosinophilia). Like t(8;21), it is a favorable-risk AML but does NOT cause severe DIC or the coagulopathy pattern described. The clinical presentation with severe thrombocytopenia and bleeding from DIC is not characteristic of inv(16) AML. ## High-Yield Facts - **t(15;17)** is the defining cytogenetic abnormality of acute promyelocytic leukemia (APL/AML-M3), creating PML-RARA fusion protein. - **DIC with severe thrombocytopenia and coagulopathy** (raised PT/aPTT, bleeding) is the pathognomonic presentation of APL, caused by release of procoagulants from abnormal promyelocytes. - **Auer rods** (often multiple, 'faggot cells') are characteristic on peripheral smear in APL and help distinguish it from other AML subtypes. - **ATRA (all-trans retinoic acid) + arsenic trioxide** is the standard induction therapy in India, with >90% complete remission rate in APL. - **t(8;21) and inv(16)** are favorable-risk AML translocations but do NOT cause DIC; t(11;22) is not a recognized AML translocation. ## Mnemonics **APL = DIC + Promyelocytes + t(15;17)** When you see **thrombocytopenia + coagulopathy + bleeding** in AML, think **APL**. The PML-RARA fusion (15;17) drives release of tissue factor → DIC. Remember: APL is the AML that **bleeds to death** without ATRA. **Favorable-Risk AML Translocations: CBF (Core Binding Factor)** t(8;21) and inv(16) are **CBF-AML** (favorable risk, ~80% 5-year survival). t(15;17) is **NOT CBF** — it is APL (highest cure rate but highest early mortality from DIC if untreated). ## NBE Trap NBE pairs coagulopathy with AML and expects students to reflexively choose a "favorable-risk" translocation like t(8;21) or inv(16). The trap is that only t(15;17) APL causes **DIC-driven coagulopathy**; the other translocations do not produce this life-threatening bleeding phenotype. ## Clinical Pearl In Indian tertiary centers, APL is now recognized as a medical emergency requiring immediate ATRA + arsenic trioxide initiation (not chemotherapy alone), as DIC-related hemorrhage is the leading cause of early death. Cytogenetic confirmation of t(15;17) should not delay treatment initiation in a clinically suspected case. _Reference: Robbins Ch. 13 (Hematopoietic and Lymphoid Systems); Harrison Ch. 110 (Acute Myeloid Leukemia)_