The Danish case-control study of cutaneous malignant melanoma. II. Importance of UV-light exposure.

A population-based case-control study of 474 patients with cutaneous malignant melanoma and 926 population controls, conducted in East Denmark over a 3-year period, included an evaluation of the relationship of UV-light exposure to cutaneous melanoma risk. Patients with lentigo maligna melanoma were not included. Significantly increased risk was associated with severe sunburn before age 15 (RR = 2.7 for 5 + vs. never), sunbathing (RR = 1.6), boating (RR = 1.4) and vacations spent in the sun (RR = 1.4 for very sunny vs. never). A significant decrease in risk was associated with occupational exposure during the summer in males (RR = 0.7), and no association with cutaneous microtopography was seen. These findings were independent of the effects of constitutional risk factors (naevi, freckles and light hair colour). No association was found between the risk of cutaneous melanoma and exposure to artificial UV-light (fluorescent light, sun lamps, or sun beds). No significant difference was found between superficial spreading melanoma and nodular melanoma with regard to any of the sun exposure variables. Our data indicate that exposure to intermittent intense sunlight is an important risk factor for cutaneous malignant melanoma, while long-term continuous exposure does not appear to be risk factor.