EFFECT OF INTERMITTENT EXPOSURE TO SUNLIGHT ON MELANOMA RISK AMONG INDOOR WORKERS AND SUN-SENSITIVE INDIVIDUALS

Intermittent exposure to sunlight is considered to be an important ris k factor for melanoma, but the associations reported in most case-cont rol studies are surprisingly weak. The aim of this study was to evalua te whether the incorporation of a subject's background exposure to the sun and pigmentation characteristics (which are assumed to influence a person's susceptibility to sunlight exposure) could produce stronger associations between sunlight expos- and the risk for melanoma. A pop ulation-based case-control study was performed in the mid-eastern part of the Netherlands. The study group comprised 141 patients with a his tologically verified melanoma and 183 controls with other malignancies who were registered by the same cancer registry. Patients with a lent igo maligna melanoma or an acrolentiginous melanoma were excluded. Inf ormation was collected by interviews and physical examination. We cate gorized subjects as indoor or outdoor workers on the basis of occupati onal exposure to the sun. Pigmentation characteristics, which are know n to be risk indicators for cutaneous melanoma, were summarized as one sun sensitivity score, We used this score to distinguish between sun- sensitive and sun-resistant persons. The odds ratios associated with s unbathing, vacations spent in sunny countries, and sunburns were highe r among the indoor workers than among the outdoor workers. After strat ification by the sun sensitivity score, the effect of sunbathing, part icipating in water sports (swimming excluded), vacations to sunny coun tries, and a history of sunburn was largest for the sun-sensitive pers ons. The data show a general trend toward higher relative risks among indoor workers and sun-sensitive individuals. The results of this stud y support the intermittent sunlight hypothesis.