What is a core component of acute promyelocytic leukemia (APL) treatment?

• A. All-trans retinoic acid (ATRA) with arsenic trioxide; induction of differentiation
• B. Chemotherapy with cyclophosphamide only
• C. Radiation therapy
• D. Watchful waiting

Answer: (A)

Targeting the differentiation arrest that characterizes APL is essential. Acute promyelocytic leukemia is driven by the PML-RARα fusion protein, which blocks maturation of promyelocytes. All-trans retinoic acid binds the RARα receptor, lifting that block and driving the leukemic promyelocytes to differentiate into mature granulocytes. Arsenic trioxide complements this by promoting degradation of the PML-RARα oncoprotein and inducing apoptosis of the malignant cells. Together, this induction of differentiation and targeted protein disruption leads to rapid remission and helps control the early coagulopathy often seen in APL. Other approaches—like chemotherapy with cyclophosphamide alone, radiation therapy, or watchful waiting—do not address the fundamental differentiation block and are not standard APL therapy.