Relationship of cutaneous malignant melanoma to individual sunlight-exposure habits.

The relationships of different histologic types of cutaneous malignant melanoma to occupational and recreational sunlight exposure, habits of clothing, sunburn histories, and use of sunscreening agents were examined in a case-control study of 507 patients and 507 matched controls in Western Australia. Variations in relationships according to the primary site of melanoma were also examined. An increased incidence rate of superficial spreading melanoma was associated with low total outdoor exposure in early adulthood and frequent participation in boating and fishing. Superficial spreading melanoma of the trunk was also related to frequency of sunbathing at ages 15-24 years and of exposure of the trunk while working outdoors. In women the rate ratio for all types of melanoma occurring on the trunk was estimated at 13.0 (95% confidence interval, 2.0-83.9) in those who wore a bikini or bathed nude at ages 15-24 years compared with those wearing a conservative one-piece bathing suit. There was little evidence that sunbathing or wearing a bikini within 10 years of case diagnosis were risk factors for melanoma of the trunk. After control of confounding due to constitutional factors, only Hutchinson's melanotic freckle melanoma showed a relationship to severe sunburn. For nodular melanoma, sunburn appeared to be protective. Although many of the results supported the hypothesis that melanomas other than the Hutchinson's melanotic freckle type are related to occasional bursts of recreational sun exposure during a susceptible period in early adult life, little support for the hypothesis was obtained when recreational sun exposure was expressed as a proportion of total outdoor exposure, which had been considered a priori to be an index of intermittent sunlight exposure.