Sister chromatid exchanges in lymphocyte cultures of patients receiving chemotherapy for malignant disorders.

The frequency of sister chromatid exchange (SCE) was studied in peripheral lymphocytes of patients receiving chemotherapy for various malignant disorders. Significantly increased SCE frequencies were recorded in six patients 2-7 weeks after CCNU treatment and in one patient 2 weeks after melphalan treatment. One patient treated with prednimustine and one treated with DTIC had SCE frequencies just within the upper limit of the control range 1-2 weeks after therapy. Normal SCE frequencies were recorded in nine patients studied at times varying from 3 days to several weeks after administration of cytostatic courses involving 5-fluorouracil, vincristine, adriamycin, cyclophosphamide, bleomycin, thioTEPA, methotrexate, and prednimustine. Radiotherapy could not be causally related to increased SCE frequencies in any of the patients. The results indicate that CCNU and melphalan, in contrast to several other chemotherapeutic agents, induce very long-lived DNA lesions, which may be of crucial importance for the development of secondary neoplasms.