Acute promyelocytic leukemia: Clinical and morphologic features and prognostic factors

The most impressive clinical feature of acute promyelocytic leukemia (APL) at diagnosis is the presence in 80% to 90% of patients of a severe hemorrhagic syndrome. Recent data favor a fibrinolytic/proteolytic process rather than a disseminated intravascular coagulation as the mechanism mainly responsible for the hemorrhagic diathesis in APL. Morphologically, two main cytologic variants have been identified: the classical hypergranular APL (M3), which represents the great majority of all APL, and the microgranular variant (M3v), which accounts for about 15% to 20% of all APL. A rare basophilic variant has also been described. With regard to prognosis, it has markedly changed from that of a rapidly fatal acute leukemia to that of a highly curable disease. This revolutionary progress was mainly due to the introduction during the 1990s of all-trans retinoic acid (ATRA) for the treatment of this disease. After the introduction of ATRA, in addition to clinical features such as hyperleukocytosis (white blood cell count > 10 × 10⁹/L) or thrombocytopenia (platelet count <10 × 10³/L) at presentation, immunophenotype markers and polymerase chain reaction status for promyelocytic leukemia/retinoic acid receptor-α during follow-up also had an impact on prognosis.