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 ionizi ng radiation. Design: Population-based case-control study. Setting: New Hampshire. Patients: A total of 592 cases of BCC and 289 cases of SCC identified throu gh a statewide surveillance system and 536 age- and sex-matched controls se lected from population lists. Main Outcome Measures: Histologically confirmed BCC and invasive SCC diagno sed between July 1, 1993, through June 30, 1995, among New Hampshire reside nts. Results: Information regarding radiotherapy and other factors was obtained through personal interviews. An attempt was made to review the radiation tr eatment records of subjects who reported a history of radiotherapy. Overall , an increased risk of both BCC and SCC was found in relation to therapeuti c 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 od ds ratio, 2.94; 95% confidence interval, 1.30-6.67) and were most pronounce d for those irradiated for acne exposure. For SCC, an association with radi otherapy was observed only among those whose skin was likely to sunburn wit h 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, th ey suggest that the risk of SCC may be increased by radiotherapy, especiall y in individuals prone to sunburn with sun exposure.