Cutaneous malignant melanoma, sun exposure, and sunscreen use: epidemiological evidence.

BACKGROUND: Cutaneous malignant melanoma is the most serious form of skin cancer and accounts for about three-quarters of all skin cancer deaths. Over the last few decades the incidence and mortality rates of melanoma have been increasing worldwide. The risk of melanoma is higher in individuals with both phenotypic susceptibility and a history of sun exposure. Therefore, recommended sun protection behaviours include wearing long-sleeved clothing, seeking shade, avoiding the sun when it is strongest, and using sunscreen lotion with a sun protection factor of 15 or higher. It has been reported, however, that the use of sunscreens does not protect against melanoma and seems to increase the duration of recreational sun exposure.
METHODS: Published epidemiological studies examining sunscreen use and melanoma have been reviewed from an epidemiological point of view, taking into account potential biases. We have classified case-control studies into four categories: (1) inconclusive studies because of major bias in control population and/or the lack of multivariate analysis; (2) no association between sunscreen use and melanoma after controlling for confounders; (3) negative association (i.e. protective effect of sunscreen); and (4) positive association. Various other epidemiological studies were also analysed.
RESULTS: These results are controversial. Two case-control studies show a protective effect of sunscreen use, while three studies showed a significant risk associated with sunscreen use. However, the discordant results, the low relative risks, the lack of dose-effect relationship and the numerous biases, especially the uncertainty that exposure (sunscreen use) preceded melanoma do not suggest a causative association between sunscreen use and melanoma. Several hypotheses could partly explain these contradictory results.