Phenotypic and genotypic risk factors for invasive melanoma by sex and body site.

Background: Cutaneous melanoma incidence varies consistently across body sites between men and women, but the underlying causes of these differences remain unclear. To date, no prospective studies have examined risk factors for melanoma separately for men and women according to body site.

Objectives: We aimed to examine the association between identified constitutional, genetic and environmental risk factors for invasive melanoma of different body sites among men and women.

Methods: We compared the association between constitutional, genetic and environmental risk factors for invasive melanoma on different body sites separately for men and women in a population-based prospective cohort study of 17 774 men and 21 070 women aged between 40 and 69 years who were residents of Queensland, Australia at baseline in 2011. Participants were followed until December 2021. We examined risk factors including hair colour, tanning ability, naevus density and proxies for high cumulative sun exposure, all self-reported at baseline. We also examined polygenic risk score (PRS) derived from summary statistics from a melanoma genome-wide association study meta-analysis.

Results: During a median 10.4 years of follow-up, 455 men and 331 women developed an incident invasive melanoma; the mean age at diagnosis was lower in women than in men (62.6 vs. 65.0 years). The most common body site was the trunk in men (45.1%), and the upper (36.8%) and lower limbs (27.4%) in women. High naevus density and proxy measures of high cumulative sun exposure were similarly associated with melanoma at all sites in men and women. In both sexes, high genetic risk was associated with melanoma on all body sites except the head and neck. We observed differences between men and women in the association between PRS and melanoma of the trunk [highest vs. lowest tertile of PRS: hazard ratio (HR) 2.78, 95% confidence interval (CI) 1.64-4.69 for men; HR 1.55, 95% CI 0.63-3.80 for women] and nonsignificant but large differences for the lower limbs (HR 5.25, 95% CI 1.80-15.27 for men; HR 1.75, 95% CI 0.88-3.47 for women).

Conclusions: While there are a number of potential explanations for these findings, this raises the possibility that genetic factors other than those related to pigmentation and naevus phenotypes may play a role in the predilection for melanoma to arise on different sites in men and women.