Therapy-related leukemia associated with chemotherapy, particularly alkylating agents and topoisomerase II inhibitors, are being reported with increasing frequency in the literature mainly after breast cancer. We also observed an increasing number of such leukemias in the data base of the specialized registry of hematological malignancies of the Côte d'Or department. Between 1980 and 1998, 156 AML and RAEB-t were registered in women in Côte d'Or. Among them, 12 occurred in women with breast cancer history (7.7%). Analysis by period of time shows a significant increase in the proportion of therapy-related leukemia secondary to breast cancer (P < 0.02). Chemotherapy including topoisomerase II inhibitors was used in 10 cases in which mitoxantrone was used in eight cases. In these eight cases, leukemia had clinical and biological characteristics usually described with topoisomerase II inhibitors but 44% were promyelocytic sub-type with the t(15;17) specific karyotypic abnormality. These data on a well-defined population demonstrate the increased proportion of therapy-related leukemia secondary to breast cancer, probably due to the use of mitoxantrone.