Prospective cohort studies about cutaneous melanoma (CM) risk are still few. Host factor- and UVR exposure data were collected prospectively by questionnaire in this population-based cohort study including 40,000 Swedish born women, aged 25-64 years at enrolment (1990). Risk for CM (Cox regression and Stepwise Cox regression [SCR], hazard ratios [HRs] with 95% Confidence Intervals [CI]) in relation to risk factors, age groups (older or younger than 40 years) and primary site, were analyzed. In 29,520 women with complete follow-up through 2007, 155 invasive and 60 in situ CM were recorded. High numbers of nevi (HR, 2.9; 95% CI, 1.7-5.0) and heredity (HR, 3.7; 95% CI, 2.0-6.8) were associated with risk for CM. SCR analysis added red hair as a risk factor. Sunbed use >10 times/year increased risk for women <40 years (HR, 2.5; 95% CI, 1.0-6.2) and a trend for risk associated with sunbathing vacations (HR, 1.4; 95% CI, 1.0-2.0) was shown for women >40 years. Trunk melanoma showed correlations with high numbers of nevi (HR, 3.0; 95% CI, 1.2-7.3) and heredity (HR, 3.2; 95% CI, 1.1-9.4). Head/neck site was correlated to sunbathing vacations (HR, 2.5; 95% CI, 1.2-5.3) and heredity (HR, 7.6; 95% CI, 1.8-31.8). Our study supports divergent etiologic pathways to CM, with high numbers of nevi correlated to increased risk for trunk CM. Furthermore, it confirms that high numbers of nevi, red hair and heredity for CM are the most important risk factors and frequent sunbed use might be a risk factor for younger women.
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