Long-term effects on the immune system following local radiation therapy for breast cancer. 4. Proliferative responses and induction of suppressor activity of the blood lymphocyte population.

The long-term effect of local irradiation for breast cancer on the blood lymphocyte population was examined in 149 women who had been disease-free for 5-6 and 10-11 years. The patients were included in a clinical trial aiming at determining the value of pre- and post-operative irradiation (45 Gy) compared to surgery only. It was observed that the relative mitogen responses of lymphocytes to phytohaemagglutinin (PHA) and Concanavalin (Con A) and in a mixed lymphocyte culture (MLC) were significantly lower in irradiated compared to unirradiated patients at least a decade after treatment. The prolonged reductions of mitogen responses after irradiation could partly be due to an increased proportion of lymphocytes which may express suppressor function since the Con A-inducible suppressor activity of lymphocytes was significantly higher in irradiated compared to unirradiated patients.