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[6 min read] Phenotypic characteristics, pattern of UV exposure, and melanoma risk on different body sites
Do phenotypic characteristics and pattern of UV radiation exposure differ according to body site of melanoma? A study investigated the association between phenotypic characteristics, pattern of UV radiation exposure, and risk of melanoma on different body sites.
Two pathways have been hypothesised for the development of cutaneous melanoma: one typically affects the head and neck, a site with chronic sun damage, and the other affects the trunk, which is less exposed to the sun. However, the possible cause of limb melanomas is less studied under this hypothesis.
A study used data on 161 ,540 women with information on phenotypic characteristics and UV radiation exposure who were part of the Norwegian Women and Cancer study, a population-based prospective study established in 1991 with exposure information collected by questionnaires at baseline and every four to six years during follow-up through to 2015.
Participants reported hair colour, eye colour, untanned skin colour, number of small symmetric and large asymmetric naevi, and freckling, as well as histories of sunburns, sunbathing vacations, and indoor tanning in childhood, adolescence, and adulthood. Primary melanoma site was categorised as head and neck, trunk, upper limbs, and lower limbs.
The study found that associations with large asymmetric naevi, sunbathing vacations, and indoor tanning differed significantly among melanoma sites. Skin colour, hair colour, small symmetric naevi, residential ambient UV radiation, and sunburns were associated with melanoma risk on all sites.
During follow-up of the 161 ,540 women in the study (mean age at study entry, 50 years; mean age at diagnosis, 60 years), 1,374 incident cases of melanoma were diagnosed. Having large asymmetric naevi was a significant risk factor for all sites and was strongest for the lower limbs (relative risk [RR], 3.38; 95% CI, 2.62-4.38) and weakest for the upper limbs (RR, 1.96; 95% CI, 1.22-3.17; P = .02 for heterogeneity).
Mean lifetime number of sunbathing vacations was significantly associated with risk of trunk melanomas (RR, 1.14; 95% CI, 1.07-1.22) and lower limb melanomas (RR, 1.12; 95% CI, 1.05-1.19) but not upper limb melanomas (RR, 0.98; 95% CI, 0.88-1.09) and head and neck melanomas (RR, 0.87; 95% CI, 0.73-1.04; P = .006 for heterogeneity).
Indoor tanning was associated only with trunk melanomas (RR for the highest tertile, 1.49; 95% CI, 1.16-1.92) and lower limb melanomas (RR for the highest tertile, 1.33; 95% CI, 1.00-1.76; P = .002 for heterogeneity). Skin colour, hair colour, small symmetric naevi, and history of sunburns were associated with risk of melanoma on all sites.
These results appear to support the hypothesis of divergent pathways to melanoma and that recreational sun exposure and indoor tanning are associated with melanoma on the lower limbs, the most common site of melanoma in women. These findings may have important preventive implications.