Acute promyelocytic leukaemia (AML – M3) includes which of the following subtypes –
**Core Concept**
Acute promyelocytic leukemia (APL), also known as AML-M3, is a subtype of acute myeloid leukemia characterized by the accumulation of immature granulocytes called promyelocytes. This subtype is associated with a specific genetic abnormality, the t(15;17) translocation, leading to the formation of the PML-RARA fusion gene.
**Why the Correct Answer is Right**
The PML-RARA fusion gene plays a crucial role in the pathogenesis of APL. It leads to the inhibition of normal granulocyte differentiation, resulting in the accumulation of promyelocytes in the bone marrow. The t(15;17) translocation is a result of a reciprocal translocation between chromosomes 15 and 17, which involves the PML gene on chromosome 15 and the RARA gene on chromosome 17. This abnormality is present in the majority of APL cases.
**Why Each Wrong Option is Incorrect**
**Option A:** AML with inv(16) is a subtype of AML characterized by the inv(16) translocation, which leads to the formation of the CBFB-MYH11 fusion gene. This is not associated with APL.
**Option B:** AML with t(8;21) is a subtype of AML characterized by the t(8;21) translocation, which leads to the formation of the RUNX1-RUNX1T1 fusion gene. This is not associated with APL.
**Option C:** AML with del(5q) is a subtype of AML characterized by a deletion of the long arm of chromosome 5, which is not associated with APL.
**Clinical Pearl / High-Yield Fact**
APL is a distinct subtype of AML characterized by its unique genetic abnormality and clinical features. It is associated with a high risk of disseminated intravascular coagulation (DIC) and bleeding complications due to the release of granule-bound tissue factor from the promyelocytes.
**Correct Answer: D.**