Cell kinetics to monitor radioresponsivity in human epidermoid carcinoma

The clinical relevance of proliferative activity as an indicator of radioresponsivity was investigated in advanced epidermoid carcinomas of the oral cavity. Proliferative activity, determined in vitro as 3H-thymidine labeling index, was assessed before starting radiotherapy and after 10 Gy. In a series of 35 patients, pretreatment proliferative activity was not indicative of response to radiotherapy. Conversely, in the same series of patients, an association was observed between an early variation of proliferative activity induced by 10 Gy and the response to the full course of radiotherapy. The effect on proliferative activity was not related to tumor volume reduction but to long-term clinical response. An inhibition of more or less than 70% was significantly correlated with long-term clinical outcome at 36 months in terms of the probability of local recurrence (29% vs 90%; p = 0.002) and overall survival (55% vs 16%; p = 0.006) at 36 months.