Parallel risk assessment of melanoma and basal cell carcinoma: skin characteristics and sun exposure

In this study we compared the strength of the association of constitutional factors and sun exposure with cutaneous malignant melanoma (CMM) and basal cell carcinoma (BCC). We analysed 260 incident cases of CMM, 425 incident cases of BCC and two sets of population controls from previous case-control studies conducted in Turin, Italy. Simultaneous comparison was accomplished by comparing separate simple logistic and polytomous logistic regressions. Tendency to sunburn was shown to be the most important risk indicator for both types of tumours, being associated with a two- to three-fold increase in risk for CMM and a two-fold increase in risk for BCC. Intermittent and intense sun exposure, as during beach holidays, increased the risk of both CMM and BCC, while prolonged exposure to sun, as during outdoor occupations, was not associated with CMM or BCC. The increase in risk during beach holidays occurred mainly during childhood for CMM cases, while for BCC cases it also continued during adulthood. Analysis of the independent effect of risk factors confirmed the role of skin phenotype (eye colour odds ratio [OR] = 1.6, tendency to sunburn OR = 2.1) and intermittent sun exposure (sunburns in childhood OR = 3.8, sun exposure during beach holidays OR = 1.2) in CMM. Risk of CMM showed a significant increase when sun exposure exceeded the threshold of about 3500 h during beach holidays cumulated in a lifetime. In contrast, the role of skin phenotype in BCC is less strong, but cumulated hours of sun exposure during beach holidays in a lifetime showed a constant risk rise with an early plateau at a low exposure level.