Which statement best differentiates acute myeloid leukemia (AML) from acute lymphoblastic leukemia (ALL)?

• A. AML arises from the myeloid lineage and often shows Auer rods; it is more common in adults.
• B. ALL arises from lymphoid precursors and never shows TdT positivity.
• C. AML typically presents with widespread lymphadenopathy, especially in children.
• D. ALL is characterized by Auer rods and MPO positivity.

Answer: (A)

Lineage origin and characteristic markers distinguish AML from ALL. AML comes from the myeloid branch of hematopoiesis and often contains Auer rods—needle-like cytoplasmic inclusions that are positive for myeloperoxidase. This combination points to a myeloid blast population. ALL, on the other hand, arises from lymphoid precursors and typically shows TdT positivity, reflecting lymphoid immaturity. AML is more common in adults, while ALL is more common in children, so that age pattern further helps differentiate them. The other statements mix up these features—Auer rods and MPO positivity are not seen in ALL, and TdT positivity is characteristic of lymphoid, not myeloid, lineage.