GENOTOXIC EFFECTS OF RADIOTHERAPY AND CHEMOTHERAPY ON THE CIRCULATING LYMPHOCYTES OF BREAST-CANCER PATIENTS .3. MEASUREMENT OF MUTANT FREQUENCY TO 6-THIOGUANINE RESISTANCE

The mutant frequencies (MF) at the HPRT locus of peripheral blood lymphocytes collected from breast cancer patients before and after treatment according to a defined protocol of the Institut Curie were compared to those from healthy donors. The treatment involved either a local radiotherapy (RT1) followed by a chemotherapy (CT2) or a chemotherapy (CT1) followed by a radiotherapy (RT2). In accord with others, we observed no significant difference in the MF to 6 thioguanine resistance (6TG) in T lymphocytes in the control and breast cancer groups before treatment. When the effect of CT or RT either alone or in combination was analysed, the increase observed in MF can be wholly accounted for by the effect of radiation. In this study, the effect of chemotherapy on mutation did not achieve significance. Circulating T lymphocytes are mainly in the G phase of the cell cycle and thus would not be mutated by drugs which preferentially affect dividing cells, whereas such cells could still mutate when submitted to ionizing radiation. © 1990 Oxford University Press.