Cytogenetic studies on acute nonlymphocytic leukemia in relapse.

Karyotypic abnormalities were compared in 42 acute nonlymphocytic leukemia patients at diagnosis and in relapse. Clonal changes were observed in 21 cases. The types of changes were the appearance of clonal abnormalities in relapse in four patients without clonal changes at diagnosis, the detection of new abnormalities superimposed on preexisting ones in 11 cases, and the selection of an abnormal clone in six others. Nonclonal structural abnormalities, mainly involving chromosomes 17 and 12p, were detected in relapse in 17 patients, compared to seven at diagnosis. The appearance of totally new clonal changes at relapse and the role of individual sensitivity to chemotherapy are discussed.