Menopausal Hormone Therapy and Risk of Melanoma: A Nationwide Register-Based Study in Finland.

Background: The association between use of menopausal hormone therapy and risk of cutaneous melanoma is highly debated. We investigated the issue in a Finnish nationwide cohort of women ages 50 years or older.
Methods: All women who had purchased hormone therapy between 1994 and 2007 were identified from the national Medical Reimbursement Registry and linked to the Finnish Cancer Registry. We calculated standardized incidence ratios (SIR) to compare incidence of cutaneous melanoma among hormone therapy users with that of the general population.
Results: During a mean follow-up of 15.6 years, 1,695 incident cutaneous melanoma cases were identified among 293,570 women who had used hormone therapy for at least 6 months. The SIRs for women who used unopposed estrogen therapy and combined estrogen-progestin therapy (EPT) for 6 to 59 months were 1.20 [95% confidence interval (CI), 1.06-1.35] and 1.00 (95% CI, 0.87-1.14; P _{heterogeneity} = 0.04). The SIRs for women who used estrogen therapy and EPT for at least 60 months were 1.37 (95% CI, 1.22-1.52) and 1.23 (95% CI, 1.13-1.34; P _{heterogeneity} = 0.15). We did not find significant differences between oral and transdermal administrations, nor between doses of estrogens.
Conclusions: Use of hormone therapy, especially estrogen therapy, was associated with an increased risk of cutaneous melanoma. EPT use of less than 5 years was not associated with an increased risk of cutaneous melanoma.
Impact: Our results add to the growing body of epidemiologic evidence that the use of unopposed estrogens in menopause increases the risk of cutaneous melanoma, while the addition of progestins might counteract the detrimental effect.
(©2019 American Association for Cancer Research.)