Appearance time of leukemic cells with t(8;21) in bone marrow.

A 30-year-old man was referred because of slight leukocytosis. The hematological findings, including those of the bone marrow, showed no evidence of leukemia. The level of neutrophil alkaline phosphatase (NAP) in the peripheral blood was normal, as were the chromosomes from bone marrow cells. Fifteen months later, the disease was diagnosed as M2 (according to the French-American-British classification) showing a t(8;21)(q22;q22) and a low NAP level as two markers of M2 cells. This is probably the first case of acute leukemia in which the cytogenetic analysis was performed before and after the appearance of a specific chromosome abnormality.