**Question:** AML with worst prognosis:

A. Acute promyelocytic leukemia
B. Acute myeloid leukemia, FAB M3 subtype
C. Acute myeloid leukemia with t(15;17) and PML-RARA fusion gene
D. Acute myeloid leukemia, FAB M4 subtype (megaloblastic)

**Core Concept:** Acute Myeloid Leukemia (AML) is a group of blood cancers characterized by rapid proliferation of immature myeloid cells in the bone marrow and blood. Different subtypes of AML are classified based on morphological, immunophenotypic, and genetic characteristics.

**Why the Correct Answer is Right:** AML with the worst prognosis is generally associated with certain genetic abnormalities and specific subtypes. In this case, AML with FAB M3 subtype (acute myeloid leukemia, FAB M3) is considered to have a poor prognosis. This subtype is characterized by the presence of the t(15;17) chromosomal abnormality and the PML-RARA fusion gene, which leads to dysregulated differentiation and proliferation of myeloid cells.

**Why Each Wrong Option is Incorrect:**

A. Acute promyelocytic leukemia (APL) is a distinct subtype of AML with a better prognosis due to the presence of the t(15;17) and PML-RARA fusion gene, which is associated with a high response rate to retinoic acid and arsenic trioxide therapies.

B. AML, FAB M4 (megaloblastic) is a subtype of AML characterized by the presence of megaloblasts (abnormally large immature granulocytes) in the bone marrow and blood, but the prognosis is generally better than FAB M3 due to a higher response to chemotherapy and less frequent involvement of extramedullary sites.

C. Acute myeloid leukemia with t(16;16) and CBFB-MYH11 fusion gene has a poor prognosis due to resistance to conventional chemotherapy and high risk of relapse.

D. Acute myeloid leukemia, FAB M5 (monocytic) is a subtype of AML characterized by the presence of immature monocytes in the bone marrow and blood. While the prognosis can be variable, it is generally better than FAB M3 due to a higher response rate to chemotherapy and less frequent involvement of extramedullary sites.

**Core Concept:** Acute Myeloid Leukemia (AML) is a group of hematologic malignancies characterized by the infiltration of the bone marrow and blood by immature myeloid cells. Different subtypes of AML are defined based on morphological, immunophenotypic, and genetic features, which can have a significant impact on prognosis and treatment options.

**Why the Correct Answer is Right:** The correct answer, AML with FAB M3 (acute myeloid leukemia, FAB M3), is characterized by the presence of t(15;17) chromosomal abnormality and the PML-RARA fusion gene. This genetic abnormality leads to dysregulated