THE MULTICENTER SOUTH EUROPEAN STUDY HELIOS .2. DIFFERENT SUN EXPOSURE PATTERNS IN THE ETIOLOGY OF BASAL-CELL AND SQUAMOUS-CELL CARCINOMAS OF THE SKIN

The role of sun exposure in development of basal cell and squamous cel l carcinomas among different populations from south Europe was investi gated. Between 1989 and 1993 we interviewed incident cases and a rando m population sample of controls from five centres where a cancer regis try was operating, whereas we selected a sample of hospital-based case s and controls from the other three centres. We gathered information o n life-long exposure to sunlight during different activities. Results are analysed for 1549 basal cell carcinoma (BCC) cases and 228 squamou s cell carcinoma (SCC) cases compared with 1795 controls. We observed a statistically significant increase of risk of SCC with increasing su n exposure beyond a threshold of 70 000 cumulated hours of exposure in a lifetime. Sun exposures during work and holidays were, however, inv ersely correlated. Odds ratios (ORs) of SCC were up to eight or nine t imes the reference for the highest exposures (200 000 cumulated hours or more). BCC exhibited a 2-fold increase of risk for lower exposure ( 8000-10 000 cumulated hours in a lifetime) with a plateau and a slight decrease of risk for the highest exposures (100 000 cumulated hours o r more). Outdoor work showed a significantly increased risk of SCC (OR 1.6 for more than 54 000 cumulated hours of exposure in a lifetime), whereas recreational activities such as sun exposure during holidays a t the beach (OR 1.6 for more than 2600 cumulated hours of exposure in a lifetime) or during water sports (OR 1.6 for more than 2600 cumulate d hours of exposure in a lifetime) were associated with an increased r isk of BCC. Risk patterns were different in poor or good tanners with a significant risk trend for good tanners, whereas poor tanners were o n a plateau of increased risk at any level of exposure. Solar radiatio n is associated with a risk of BCC even for relatively short periods o f exposure such as during holidays and sports, whereas SCC develops la ter if exposure continues. The skin's ability to tan modulates the ris k of BCC; subjects who lan poorly have a steady risk increase, whereas people who tan easily develop cancer only after prolonged exposures.