Acute promyelocytic leukemia (APL) is a clinically and biologically distinct variant of acute myeloid leukemia (AML). It was classified as AML-M3 in the older French-American-British (FAB) classification system, and acute promyelocytic leukemia with t(15;17)(q24.1;q21.1);PML-RARA in the WHO classification system. (See "Classification of acute myeloid leukemia".)
The vast majority of patients with newly diagnosed APL can obtain a complete remission with induction therapy that incorporates all-trans retinoic acid (ATRA; tretinoin) followed by a molecular complete remission after consolidation therapy. It is extremely uncommon to have primary drug resistance in APL, and in general, the predominant cause of induction failure (5 to 10 percent) is death from hemorrhage or infection. Despite this, relapse occurs in 10 to 15 percent of patients with APL and in about 20 to 30 percent of those with high-risk APL as defined as those who present with a white blood cell count above 10,000 and a platelet count less than 40,000. Using arsenic trioxide (ATO) during consolidation of first complete remission may markedly reduce the relapse rate even in high-risk APL.
The treatment of relapsed or refractory APL will be reviewed here. The clinical features, diagnosis, and prognosis of APL in adults are presented separately, as is the initial treatment of APL. (See "Clinical manifestations, pathologic features, and diagnosis of acute promyelocytic leukemia in adults" and "Initial treatment of acute promyelocytic leukemia in adults".)
Resistant or refractory acute promyelocytic leukemia (APL) is diagnosed in those patients who either fail to attain a cytologic complete remission with induction chemotherapy or fail to attain a complete molecular remission following several cycles of consolidation chemotherapy. Response criteria are presented separately. (See "Remission criteria in acute myeloid leukemia and monitoring for residual disease".)
We consider patients to have relapsed disease if, after attainment of complete molecular remission, subsequent analyses confirm the loss of such molecular remission or identify extramedullary disease.