Preleukemia: hematological disorders prior to onset of leukemia.

Published data on Japanese leukemia patients with a preleukemic hematological disorder were assessed. The reexamined cases were from the "Japona Centra Revuo Medicina" reported during the period from 1952 to 1971. Among preleukemic hematological disorders, hypoplastic anemia was the most frequently reported (41 of 62 cases). These "hypoplastic preleukemia" patients were rather elderly and terminated mostly in atypical myelocytic leukemia. The chief hematological feature of the hypoplastic preleukemia cases was the coexistence of a relative erythroid hyperplasia and a slight increase of myeloblasts in the bone marrow that was unusual in hypoplastic anemia. The presence of pancytopenia and hypocellular marrow with a relative erythroid hyperplasia combined with a slight increase of myeloblasts probably indicates hypoplastic preleukemia that terminates later in acute leukemia.