What is Acute Promyelocytic Leukemia?
Acute Promyelocytic Leukemia is a variant of Acute Myelogenous Leukemia, which is called M3 in the FAB classification and acute promyelocytic leukemia in the WHO classification, occurs at any age and constitutes approximately 10 percent of Acute Myelogenous Leukemia cases. This subtype of Acute Myelogenous Leukemia occurs with greater than expected frequency among Latinos from Europe and South and Central America and among patients with an increased body mass index. Unlike all other major variants of Acute Myelogenous Leukemia, which increase in incidence logarithmically with age, the incidence of Acute Promyelocytic Leukemia is constant over the human life span.
Special manifestations of Acute Promyelocytic Leukemia
Hemorrhagic manifestations are prominent including hemoptysis, hematuria, vaginal bleeding, melena, hematemesis, and pulmonary and intracranial bleeding, as well as the more typical skin and mucous membrane bleeding. In severely leukopenic patients, blasts may not be evident in the blood. Moderately severe thrombocytopenia <50 x 109/L is present in most cases. The marrow contains few agranular blast cells and some blast-like cells with scant granules. The dominant cells are promyelocytes, which comprise 30 to 90 percent of marrow cells. Auer rods and cells with multiple Auer rods (1–10%) are present in nearwith multiple Auer rods have been referred to as faggot cells.
A propensity to hemorrhage is a striking feature of this subtype. The prothrombin and partial thromboplastin times are prolonged, and the plasma fibrinogen level is decreased in most cases. The disturbance in coagulation first was thought to principally result from intravascular coagulation initiated by procoagulant released from the granules of the leukemic promyelocytes.
Treatment of Acute Promyelocytic Leukemia
Although Acute Promyelocytic Leukemia responded to chemotherapy regimens for Acute Myelogenous Leukemia, especially those containing an anthracycline antibiotic such as daunomycin or rubidazone,the cytologic pattern of response in the marrow often was paradoxical.
Persistence of leukemic promyelocytes preceded remission in the absence of further therapy, whereas induction of marrow cell hypoplasia was classically considered a requirement for remission in patients with Acute Myelogenous Leukemia. Generally, if leukemic blast cells persist after therapy for Acute Myelogenous Leukemia, relapse ensues unless hypoplasia is induced by more cytotoxic therapy. The unusual pattern of response in Acute Promyelocytic Leukemia was put into context by reports of successful treatment with isomers of retinoic acid, an agent that leads to maturation of leukemic promyelocytes in vitro.