Do sex and site matter?: Different age distribution in melanoma of the trunk among Swedish men and women

Background Recent research on cutaneous malignant melanoma (CMM) points to the coexistence of several biological pathways linked to the anatomical site of the lesion, which could lead to this neoplasm. Although the different anatomical distribution of CMM by sex is usually attributed to gender-specific patterns of sun exposure, it has been suggested that an alternative explanation might lie in gender-specific site susceptibility. Objectives This paper aimed at analysing the age distribution of CMM by site and sex to gain in-depth knowledge of differences between the sexes. Methods Using a large Swedish cohort comprising 2 992 166 workers, Poisson models were fitted to estimate age-specific incidence rates by site and sex, duly adjusted for several factors that might account for changes in environmental exposures (period, birth cohort, socioeconomic level, latitude and rurality). Results Incidence rates were 17.4 cases per 100 000 person-years in men and 16.5 in women. Sex differences were particularly striking for CMM of the trunk, where both crude and adjusted incidence rates displayed a steady increase with age in men, but reached a plateau in women at around four cases per 100 000 person-years from the 40-45-year age group (perimenopausal period) upwards. There was an almost fivefold increase in the sex ratio for this body site between the younger and older age groups, a difference which could not be attributed to period or cohort effects. Conclusions If different aetiological pathways can be assumed to lead to melanoma, then disparities between men and women, particularly in CMM of the trunk, suggest that a possible interaction between site and sex should be borne in mind.