Risk of malignant melanoma in men with prostate cancer. Nationwide, population-based cohort study.

An increased risk of malignant melanoma has been observed in men with prostate cancer. To assess potential shared risk factors and confounding factors, we analysed risk of melanoma in men with prostate cancer including information on tumor characteristics and demographics including socioeconomic status. In The Prostate Cancer data Base Sweden, risk of melanoma was assessed in a cohort of men with prostate cancer and in a comparison cohort of prostate-cancer free men. Data on prostate cancer risk category, melanoma stage, basal cell carcinoma, location of residency, and socioeconomic status were obtained from nationwide registers. Melanoma was diagnosed in 830/108,145 (0.78%) men with prostate cancer and in 3,699/556,792 (0.66%) prostate cancer-free men. In multivariable Cox regression models, men with prostate cancer had a significantly increased risk of melanoma (HR 1.18, 95% CI 1.09-1.27), and so had married men, men with high education and income, and men residing in southern Sweden. The strongest associations were observed for stage 0 melanoma in men with low-risk prostate cancer (HR 1.45, 1.14-1.86), high education (HR 1.87, 1.60-2.18) and top income (HR 1.61, 1.34-1.93), respectively, whereas there was no association between these factors and late-stage melanoma. Men with prostate cancer also had an increased risk of basal cell carcinoma (HR 1.18, 1.15-1.22). In conclusion, men with low-risk prostate cancer, high education, high income and residency in southern Sweden had an increased risk of early-stage melanoma.