The role of all-trans-retinoic acid in the treatment of acute promyelocytic leukemia.

All-trans-retinoic acid (ATRA) has demonstrated in vivo and in vitro that it could differentiate leukemic cells in acute promyelocytic leukemia (APL). ATRA yields complete remission (CR) rates of approximately 90% in newly diagnosed and first relapsing APL, in APL resistant to one or two courses of chemotherapy, whereas patients in second and subsequent remissions often have only partial remissions. The use of ATRA in APL is associated with two major drawbacks: (1) the risk of rapidly rising leukocyte counts, leading to the 'retinoic acid syndrome' which may be fatal if the increase in leukocytes is not reversed and (2) almost universal relapse, if no intensive chemotherapy is administered after CR achievement. Preliminary results, however, suggest that ATRA followed by intensive chemotherapy has improved the outcome of newly diagnosed APL, by slightly increasing the CR rate but also by reducing the risk of relapse, as compared to chemotherapy alone.