Acute promyelocytic leukemia.

The treatment of acute promyelocytic leukemia (APL) is different from other subtypes of acute myelocytic leukemia (AML). All trans-retinoic acid (ATRA) is an essential component of the standard remission induction for all newly diagnosed APL patients. Remission induction with ATRA and chemotherapy given concurrently appears to be associated with fewer relapses. With further consolidation chemotherapy without high-dose cytosine arabinoside, the disease-free survival rate can reach 70% to 80%, and many of these patients are cured, more so than in any other AML subtype. APL is especially sensitive to anthracyclines, which should be included in the chemotherapy cycles at a higher dose than in other AML subtypes. Maintenance with low-dose chemotherapy (oral daily 6-mercaptopurine with weekly methotrexate) or ATRA further improves the long-term outcome. New approaches are also available for relapsing patients, although the optimal treatment is unknown. Patients who did not receive oral ATRA in first relapse can be treated with this agent, as can first relapsing patients who have been off the drug for more than 1 year. Because of poor remission rates, ATRA should not be used in patients with second or subsequent relapses (whether ATRA was given in the past), in patients with relapses early after ATRA discontinuation, or in patients relapsing while on ATRA therapy. Arsenic trioxide can also be used, especially in patients resistant to ATRA. Because arsenic trioxide is still experimental and not yet widely available, patients who are unlikely to respond to ATRA or who unsuccessfully undergo ATRA reinduction should be treated with chemotherapy. Patients in second or subsequent remission induced with ATRA or chemotherapy should receive consolidation chemotherapy. When arsenic trioxide is used for reinduction, the drug should be continued for several cycles; however, adding consolidation chemotherapy might improve the results. Because it is unknown whether APL in second or subsequent remission is curable with salvage therapy, allogeneic hematopoietic stem cell transplantation is often considered for patients with a human leukocyte antigen (HL-A)-identical sibling and autologous transplantation when a donor does not exist. However, compared with the new treatments, the role of transplantation for relapse is unclear. In first remission, there is no role for transplantation. A new liposomal formulation of intravenous ATRA is being investigated and seems effective in late first relapses, and it may be able to induce and maintain first remissions in selected patients without chemotherapy.