Patterns of Ultraviolet Radiation Exposure and Skin Cancer Risk: the E3N-SunExp Study.

Background: While ultraviolet (UV) radiation exposure is a recognized risk factor for skin cancer, associations are complex and few studies have allowed a direct comparison of exposure profiles associated with cutaneous melanoma, basal-cell carcinoma (BCC), and squamous-cell carcinoma (SCC) within a single population. Methods: We examined associations between UV exposures and skin cancer risk in a nested case-control study within E3N, a prospective cohort of 98,995 French women born in 1925-1950. In 2008, a lifetime UV exposure questionnaire was sent to all reported skin cancer cases and three controls per case, which were matched on age, county of birth, and education. Analyses were performed using conditional logistic regression and included 366 melanoma cases, 1,027 BCC cases, 165 SCC cases, and 3,647 controls. Results: A history of severe sunburns < 25 years was associated with increased risks of all skin cancers (melanoma: OR 2.7; BCC: OR 1.7; SCC: OR 2.0 for >= 6 sunburns vs. none), while sunburns >= 25 years were associated with BCC and SCC only. While high-sun protection factor sunscreen use before age 25 was associated with lower BCC risk (P-trend = 0.02), use since age 25 and reapplication of sunscreen were associated with higher risks of all three types of skin cancer. There were positive linear associations between total UV score and risks of BCC (P-trend = 0.01) and SCC (P-trend = 0.09), but not melanoma. While recreational UV score was strongly associated with BCC, total and residential UV scores were more strongly associated with SCC. Conclusions: Melanoma, BCC, and SCC are associated with different sun exposure profiles in women.