Chromosomal radiosensitivity in G₂ -phase lymphocytes identifies breast cancer patients with distinctive tumour characteristics

A substantial proportion of women with breast cancer exhibit an abnormally high radiosensitivity as measured by the frequency of chromatid breaks induced in G(2)-phase, PHA stimulated lymphocytes. Chromatid break frequencies were compared for a cohort of previously untreated sporadic breast cancer patients and hospital outpatient controls, In the breast cancer group 46% showed high radiosensitivity compared to 14% of controls (P < 0.001). Comparison of those breast cancer patients with a high G(2) radiosensitivity (G(2)RS) versus those with a low G(2)RS showed no difference in menopausal status or age but the high G(2)RS group had on average a lower score on the Nottingham Prognostic Index. Predicted survival in the high G(2)RS group at 15 years was 55% compared to 36% for the low G(2)RS group. Furthermore, 81% of tumours from the high G(2)RS were oestrogen receptor positive compared to 45% from the low G(2)RS group. Thus high G(2)RS identifies a sub-population of patients with distinctive tumour characteristics and with a predicted improved prognosis as compared with those in the low G(2)RS group. Our findings imply that besides influencing risk of breast cancer the genetic factors determining G(2) radiosensitivity also influence the tumour characteristics and prognosis in these patients. (C) 2001 Cancer Research Campaign.