The differential response of human tumours to fractionated radiation may be due to a post-irradiation repair process.

We have measured post-irradiation recovery (potentially lethal damage repair) after fractionated radiation in plateau-phase cultures of two human tumour cell lines derived from tumours of different radiocurabilities (melanoma and breast). Although the radiation survival-curve parameters of these cell lines are similar, the repair of potentially lethal X-ray damage after fractionated X-ray treatment conferred significant radioresistance on the human melanoma cells but not the human breast carcinoma cells. We suggest that the repair of potentially lethal damage may correlate with clinical radiocurability.