Cytogenetic studies of leukemic recurrence in recipients of bone marrow allografts.

Cytogenetic studies were made in 20 leukemic patients who relapsed after treatment by allogeneic bone marrow transplantation (BMT). Seven of the eight patients in whom no chromosomal abnormalities were detected in leukemic cells before BMT developed clonal abnormalities after BMT, and in two of these patients two independent clones were observed. Most patients in whom clones were detected before BMT showed evidence of clonal evolution after BMT. Nonclonal abnormalities were also observed in clonal cells. These additional abnormalities, both clonal and nonclonal, were attributed to the effects of total body irradiation received by the patient before BMT. There was no evidence of recurrence of leukemia in donor cells among these patients. We concluded that the cells found in leukemic recurrence were derived from the original leukemic clone.