What condition is treated by all-trans retinoic acid?

All-trans retinoic acid is primarily used in the treatment of acute promyelocytic leukemia (APL), which is a distinct subtype of acute myeloid leukemia characterized by the presence of promyelocyte proliferation, often associated with a specific chromosomal translocation involving the promyelocytic leukemia (PML) gene and the retinoic acid receptor (RARA) gene. This translocation interferes with normal myeloid differentiation, leading to the accumulation of immature promyelocytes in the bone marrow.

The mechanism of action for all-trans retinoic acid involves promoting maturation of these abnormal promyelocytes into functional granulocytes. By doing so, it effectively reverses the leukemic process, allowing for treatment-induced differentiation and significant improvement in patient outcomes when combined with chemotherapy.

In contrast, acute myeloid leukemia, chronic lymphocytic leukemia, and non-Hodgkin lymphoma do not specifically rely on retinoic acid for treatment. APL is unique in its response to all-trans retinoic acid, making it the correct answer in this context.