Ambient temperature and risk of first primary basal cell carcinoma: A nationwide United States cohort study.

The Earth's surface is warming and animal studies have shown higher temperatures promote ultraviolet radiation (UVR) skin carcinogenesis. There are, however, no population studies of long-term temperature exposure and basal cell carcinoma (BCC) risk. We linked average lifetime summer ambient temperatures (based on weather station data) and satellite-based UVR estimates to self-reported lifetime residences in the U.S. Radiologic Technologists' cohort. We assessed the relationship between time-dependent average lifetime summer ambient temperature (20-year lag) in quintiles and BCC in whites, using Cox proportional hazards regression. Risks were adjusted for time-dependent lagged average lifetime UVR and time outdoors, body mass index, eye color, and sex (baseline hazard stratified on birth cohort). During a median 19.4 years follow-up, we identified 3556 BCC cases. There was no significant trend in risk between temperature and BCC. However, BCC risk was highest in the fourth quintile of temperature (Q4 vs. Q1; hazards ratio (HR)=1.18; 95% confidence interval (CI)=1.06-1.31, p-trend=0.09). BCC risk was strongly related to average lifetime ambient UVR exposure (Q5 vs. Q1; HR=1.54 (95% CI=1.35-1.75, p-trend=<0.001)). Future studies of temperature and BCC risk should include a broad range of UVR and temperature values, along with improved indicators of exposure to temperatures and UVR.