Association of known melanoma risk factors with primary melanoma of the scalp and neck

Background: Scalp and neck (SN) melanoma confers a worse prognosis than melanoma of other sites but little is known about its determinants. We aimed to identify associations between SN melanoma and known risk genes, phenotypic traits, and sun exposure patterns. Methods: Participants were cases from the Western Australian Melanoma Health Study (n = 1,200) and the Genes, Environment, and Melanoma Study (n = 3,280). Associations between risk factors and SN melanoma, compared with truncal and arm/leg melanoma, were investigated using binomial logistic regression. Facial melanoma was also compared with the trunk and extremities, to evaluate whether associations were subregion specific, or reflective of the whole head/neck region. Results: Compared with other sites, increased odds of SN and facial melanoma were observed in older individuals [SN: OR = 1.28, 95% confidence interval (CI) = 0.92–1.80, Ptrend = 0.016; Face: OR = 4.57, 95% CI = 3.34–6.35, Ptrend < 0.001] and those carrying IRF4-rs12203592*T (SN: OR = 1.35, 95% CI = 1.12–1.63, Ptrend = 0.002; Face: OR = 1.29, 95% CI = 1.10–1.50, Ptrend = 0.001). Decreased odds were observed for females (SN: OR = 0.49, 95% CI = 0.37–0.64, P < 0.001; Face: OR = 0.66, 95% CI = 0.53–0.82, P < 0.001) and the presence of nevi (SN: OR = 0.66, 95% CI = 0.49–0.89, P = 0.006; Face: OR = 0.65, 95% CI = 0.52–0.83, P < 0.001). Conclusions: Differences observed between SN melanoma and other sites were also observed for facial melanoma. Factors previously associated with the broader head and neck region, notably older age, may be driven by the facial subregion. A novel finding was the association of IRF4-rs12203592 with both SN and facial melanoma. Impact: Understanding the epidemiology of site-specific melanoma will enable tailored strategies for risk factor reduction and site-specific screening campaigns.