Cutaneous Melanoma in Women I. Exposure to Sunlight, Ability to Tan, and Other Risk Factors Related to Ultraviolet Light

Abstract

A population-based case-control study of cutaneous malignant melanoma (CMM) was conducted in 452 women with melanoma and 930 control subjects aged 25-59 years in five San Francisco Bay Area counties between 1981 and 1986. Women were interviewed in their homes with regard to history of sunlight exposure and sunburns during different periods in their lives, phenotypic and host characteristics, medical history, occupation, and demographic factors. Data were analyzed by the patients' histologic type of melanoma; 355 women were classified as having superficial spreading melanoma (SSM), 61 had nodular melanoma (NM), 13 had lentigo maligna melanoma, and 23 had other melanomas that could not be further classified upon histologic review by University of California dermatopathologists. Univariate results from analysis of factors related to sun exposure showed that the risk of all histologic types of CMM, SSM, and NM increased with increasing tendency of the subject to sunburn and with history of increased severity and/or frequency of sunburns up to age 12 years. Risk of all types of CMM and SSM also increased with increasing number of sunburns for all age groups and with lack of use of sunscreen. After adjustment for each other and for phenotypic factors, history of sunburn up to age 12 and lack of sunscreen use were the primary sun-related factors associated with an increased risk of all types of CMM and SSM, while tendency to sunburn when exposed to 1/2 hour of noontime sun and lack of use of sunscreen were related to NM. Although having frequent sunburns before age 12 and having severe sunburns before age 12 were both strongly associated with melanoma, having large numbers of sunburns during any time period from elementary school through age 30 years and having sunburns during the 10 years prior to diagnosis or interview were all associated with a doubling of risk for SSM after adjustment for other factors. These results suggest that the increased risk of melanoma related to sunburns is not confined to childhood sunburns. Maintenance of an all-year tan provided no protective effect against melanoma after adjustment for tendency to burn. No association was noted with use of fluorescent lights or exposure to sunlamps for all types of CMM, SSM, or NM.