Acute Lymphoblastic Leukemias

Acute lymphoblastic leukemias (ALLs) are a group of hematological neoplasias defined by cytomorphology, cytochemistry, immunological markers, and more recently, molecular markers. The prognosis of ALL has much improved in the last 30 yr, especially in the age group between 2 and 10 yr, where most patients can be cured by chemotherapy. The incidence of ALL is lower than for acute myelogenous leukemia (AML) (∼1–2 cases per 100,000 inhabitants in Western countries per year). In contrast to AML, a bimodal age peak is found in ALL: most cases occur in children (with a peak incidence of 10 per 100,000 at 3 yr) and young adults followed by a second age peak beyond 60 yr. The peak is more pronounced in whites, higher socioeconomic strata, and industrialized nations in the Western hemisphere, and is mainly due to early pre-B-cell ALL. Although recent studies in the United States, the United Kingdom, and Italy seem to implicate an increased incidence of early pre-B-cell ALL as being responsible for an increase in incidence of B-lineage ALL, a very large study in Nordic countries did not mirror this finding. It could be partially explained by a concomitant decrease in incidence of undifferentiated ALL due to improved methods of diagnosis. ALL is four times as common as AML in children. In the United States, about 3000–4000 new cases of ALL are diagnosed each year; of these, about 2500 are children.