Menopausal hormone therapy and risk of melanoma: Do estrogens and progestins have a different role?

The association between use of menopausal hormone therapy (HT) and occurrence of skin malignant melanoma (SMM) is controversial. We investigated the issue in a nationwide cohort of 684,696 Norwegian women, aged 45-79 years, followed from 2004 to 2008. The study was based on linkage between Norwegian population registries. Multivariable Poisson regression models were used to estimate the effect of HT use, different HT types, routes of administration and doses of estrogen and progestin on the risk of SMM. During the median follow-up of 4.8 years, 178,307 (26%) women used HT, and 1,476 incident SMM cases were identified. Current use of HT was associated with increased risk of SMM (rate ratios (RR) = 1.19; 95% confidence interval (CI) 1.03-1.37). Plain estrogen therapy was associated with an increased risk of 5MM (RR 1.45; 95% CI 1.21-1.73), both for oral (RR 1.45; 95% CI 1.09-1.93) and vaginal (RR 1.44; 95% CI 1.14-1.84) formulations, while combined estrogen and progestin therapy (EPT) was not (RR 0.91; 95% CI 0.70-1.19). We performed a dose-response analysis of estrogen and progestin in women using tablets, and found that use of estrogens was associated with increased risk (RR 1.24; 95% CI 1.00-1.53 per 1 mg/day) and use of progestins with decreased risk (RR 0.71; 95% CI 0.57-0.89 per 10 mg/month) of 5MM. In conclusion, estrogens were associated with increased risk of SMM, while combinations of estrogens and progestins were not. Our results suggest that estrogens and progestins might affect the risk of SMM in opposite ways.