Therapeutic ionizing radiation and the incidence of basal cell carcinoma and squamous cell carcinoma

Objective: To estimate the relative risk of developing basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) after receiving therapeutic ionizing radiation. Design: Population-based case-control study. Setting: New Hampshire. Patients: A total of 592 cases of BCC and 289 cases of SCC identified through a statewide surveillance system and 536 age- and sex-matched controls selected from population lists. Main Outcome Measures: Histologically confirmed BCC and invasive SCC diagnosed between July 1, 1993, through June 30, 1995, among New Hampshire residents. Results: Information regarding radiotherapy and other factors was obtained through personal interviews. An attempt was made to review the radiation treatment records of subjects who reported a history of radiotherapy. Overall, an increased risk of both BCC and SCC was found in relation to therapeutic ionizing radiation. Elevated risks were confined to the site of radiation exposure (BCC odds ratio, 3.30; 95% confidence interval, 1.60-6.81; SCC odds ratio, 2.94; 95% confidence interval, 1.30-6.67) and were most pronounced for those irradiated for acne exposure. For SCC, an association with radiotherapy was observed only among those whose skin was likely to sunburn with sun exposure. Conclusions: These results largely agree with those of previous studies on the risk of BCC in relation to ionizing radiation exposure. In addition, they suggest that the risk of SCC may be increased by radiotherapy, especially in individuals prone to sunburn with sun exposure.