Sunlight is the principal environmental risk factor for keratinocyte cancers, but other carcinogens have also been implicated, including tobacco smoke. Findings have been conflicting, however. We investigated associations between cigarette smoking and incidence of basal cell carcinoma (BCC) or squamous cell carcinoma (SCC) in QSkin, a prospective study of skin cancer (N = 43,794). Smoking history was self-reported at baseline; newly diagnosed BCCs and SCCs were ascertained through data linkage and verified by histopathology reports. We restricted analyses to white participants who at baseline reported no past history of skin cancer excisions and no more than five destructively treated actinic skin lesions. We fitted Cox proportional hazards models, adjusted for known confounders. Compared with never smokers, current smokers had significantly lower risks of BCC (hazard ratio = 0.6; 95% confidence interval = 0.4-0.9) but significantly higher risks of SCC (hazard ratio = 2.3; 95% confidence interval = 1.5-3.6). Former smokers had similar risks for BCC and SCC as never smokers. Among smokers, we observed no dose-response trends with duration of smoking, intensity, or time since quitting. On further analysis, current smokers had fewer skin examinations and procedures than never smokers, suggesting greater opportunities for detection among never smokers. Strengths include large sample size, prospective design, and virtually complete follow-up; however, histologic details were missing for a proportion of excised tumors. In conclusion, current smokers had a lower incidence of BCC (possibly because of detection bias) but higher rates of SCC.
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