Nevus Count, Pigmentary Characteristics, and Melanoma-specific Mortality among Norwegian Women with Melanoma >1.0 mm Thick

Little is known about if and how nevi and pigmentation are associated with melanoma-specific mortality. However, increased melanoma awareness in people with lighter pigmentation and many nevi may result in earlier diagnosis of thinner less-lethal tumors. The aim of this study was to investigate associations between nevus count (asymmetrical > 5 mm and small symmetrical), pigmentary characteristics (hair colour, eye colour, skin colour, freckling, pigmentary score), and melanoma-specific mortality in subjects with melanomas > 1 mm. Data from the Norwegian Women and Cancer cohort, established in 1991, with complete follow-up of melanoma patients until 2018 through the Cancer Registry of Norway, were used to estimate hazard ratios with 95% confidence intervals for the associations between nevus count, pigmentary characteristics, and melanoma-specific mortality, stratified by tumor thickness using Cox regression. Estimated hazard ratios consistently indicated a higher risk of melanoma death for those with darker vs lighter pigmentary characteristics in patients with tumors > 1.0–2.0 mm and > 2.0 mm thick (e.g. pigmentary score hazard ratio 1.25, 95% confidence interval (0.74–2.13)). Among women with melanomas > 1.0 mm thick, lighter pigmentation and asymmetrical nevi may be associated with lower melanoma-specific mortality, suggesting that factors that increase the risk of melanoma may also be associated with decreased risk of death from melanoma. SIGNIFICANCE Naevi, fair complexion, and a tendency to sunburn are well-known risk factors for melanoma, but have been less studied as prognostic factors. This population-based cohort study among women with primary invasive melanomas >1.0 mm thick suggests a higher risk of melanoma death among women with darker vs lighter hair, eye and skin colour, higher pigmentary score, and milder skin reaction to acute sun exposure. The results also indicate an interaction effect, with poorer survival in darker individuals with asymmetrical nevi >5 mm. More research is needed to understand the differential diagnostic outcomes among those with and without traditional melanoma risk factors.