Evaluation of the radioinduced damage and DNA repair capacity of breast cancer patients by the comet assay (single cell gel electrophoresis)

The genetic damage induced by ionizing radiation and the repair capacity of three breast cancer patients and three health subjects were investigated by comet assay using two parameters: tail length and visual classification. Blood samples were exposed in vitro to 60 Co gamma rays (0.6 Gy.min-1), with 0.2 to 10 Gy and analyzed just after the exposition, 3 and 24 hour after, The basal level of damage was higher in leukocytes of breast cancer patients than in health subjects. Maybe it could be affected by the age, disease stage and repair capacity. Concerning the radioinduced damage, the results showed that both groups presented a similar response when analyzed just after the irradiation. But while the health subjects had a considerable reduction of the damage after 3 hours, the patients had a residual significant damage amount even 24 hours after the exposition. The repair capacity evaluation of health subjects were almost completed within 3 hours, in contrast to the patients who had many lesions not repaired even after 24 hours. The adopted parameters showed to be secure, sensible and reproducible. The dose-response curves obtained for DNA migration can be utilised not only for cellular radiosensitivity studies but also for biological dosimetry purpose. The results allowed to conclude that the breast cancer patients presented a similar initial radiosensitivity to the health subjects, but a less efficient repair mechanism making them more vulnerable to environmental genotoxic agents. (author)