Distinctive lower incidence rates of cutaneous melanoma on the hips and lower extremities of men

Abstract

Background: Cutaneous melanomas (CMs) are more frequently found on the trunk in men, and on the hip and lower extremities (legs) in women. This discrepancy has been attributed to greater exposure to ultraviolet (UV) radiation of women's legs due to their dressing habits.

Objectives: To understand the sex difference in the bodily distribution of CMs, especially those on the legs.

Methods: This was a cancer registry-based cohort study. CM incidences, relative tumour density and tumour mutational burdens (TMBs) were compared among different body sites in different sex and racial groups using the SEER (Surveillance, Epidemiology, and End Results) and TCGA SKCM (The Cancer Genome Atlas skin cutaneous melanoma) databases.

Results: White men had lower rates and lower relative tumour density (RTD) of CMs on their legs compared with the rest of their body sites, or compared with White women. Men classified by SEER into racial groups other than White did not show such a trend. White women had comparable RTDs among different body sites. The ratios between the 'White' and the 'other' groups were used to evaluate the approximate effect of sun exposure at different body sites, which further validated a distinct protective effect of men's legs in melanoma. TMB on leg melanomas was lower than on other sites in both sexes.

Conclusions: The legs of both sexes in White patients show lower RTDs and lower levels of TMB, suggesting a weaker association with UV exposure. Furthermore, White men are especially protected against CM on their legs, suggesting an unknown intrinsic protective factor as compared with women.