Lifestyle differences in twin pairs discordant for basal cell carcinoma of the skin

Background: Basal cell carcinoma (BCC) of the skin is a multifactorial disease with a complex interplay of genetic, environmental and lifestyle factors, including patterns of solar exposure, with childhood exposure being of particular relevance. Case-control studies in disease-discordant twin pairs adjust for familial factors and improve the power of conventional case-control studies. Objectives: To investigate the roles of sociodemographic, dietary, medication, hormonal and other lifestyle factors in the aetiology of BCC. Methods: The study base comprised all same-sex twins who had answered the baseline health questionnaire of the Finnish Adult Twin Cohort Study in 1975. Information on all histologically confirmed cases of BCC was retrieved from the nationwide cancer registry. The first twin to have BCC was defined as the case and his/her co-twin (alive at the time of diagnosis) as the control. Only pairs with the first BCC between 1976 and 1999 were included in the study (n = 333). Conditional logistic regression analyses were used to assess BCC risk by study factors. Results: A significantly increased risk was associated with smoking status in females but not in males. The risk was higher in dizygotic than in monozygotic females, possibly indicating the presence of a gene-smoking interaction. Suggestive but statistically nonsignificant increases in risk were observed for higher education, urticaria and atopic eczema, use of nonsteroidal antiinflammatory drugs and coffee. A suggestive risk decrease was observed for outdoor work. No clear effects were observed for marital status, body mass index, use of alcohol, tea, fruit and vegetables or oral contraceptives. Conclusions: The results suggest a role for smoking and possibly also for other lifestyle factors in the risk of contracting BCC.