MDM2-SNP309 (rs2279744), a common genetic modifier of cancer incidence in Li-Fraumeni syndrome, modifies risk, age of onset, or prognosis in a variety of cancers. Melanoma incidence and outcomes vary by sex, and although SNP309 exerts an effect on the estrogen receptor, no consensus exists on its effect on melanoma. MDM2 and MDM4 restrain p53-mediated tumor suppression, independently or together. We investigated SNP309, an a priori MDM4-rs4245739, and two coinherited variants, in a population-based cohort of 3663 primary incident melanomas. Per-allele and per-haplotype (MDM2_SNP309-SNP285; MDM4_rs4245739-rs1563828) odds ratios (OR) for multiple-melanoma were estimated with logistic regression models. Hazard ratios (HR) for melanoma death were estimated with Cox proportional hazards models. In analyses adjusted for covariates, females carrying MDM4-rs4245739*C were more likely to develop multiple melanomas (OR_per-allele = 1.25, 95% CI 1.03-1.51, and P_trend = 0.03), while MDM2-rs2279744*G was inversely associated with melanoma-death (HR_per-allele = 0.63, 95% CI 0.42-0.95, and P_trend = 0.03). We identified 16 coinherited expression quantitative loci that control the expression of MDM2, MDM4, and other genes in the skin, brain, and lungs. Our results suggest that MDM4/MDM2 variants are associated with the development of subsequent primaries and with the death of melanoma in a sex-dependent manner. Further investigations of the complex MDM2/MDM4 motif, and its contribution to the tumor microenvironment and observed associations, are warranted.

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, P _trend = 0.016; Face: OR = 4.57, 95% CI = 3.34-6.35, P _trend < 0.001] and those carrying IRF4-rs12203592*T (SN: OR = 1.35, 95% CI = 1.12-1.63, P _trend = 0.002; Face: OR = 1.29, 95% CI = 1.10-1.50, P _trend = 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.

Genome-wide association studies (GWAS) have led to the identification of hundreds of susceptibility loci across cancers, but the impact of further studies remains uncertain. Here we analyse summary-level data from GWAS of European ancestry across fourteen cancer sites to estimate the number of common susceptibility variants (polygenicity) and underlying effect-size distribution. All cancers show a high degree of polygenicity, involving at a minimum of thousands of loci. We project that sample sizes required to explain 80% of GWAS heritability vary from 60,000 cases for testicular to over 1,000,000 cases for lung cancer. The maximum relative risk achievable for subjects at the 99th risk percentile of underlying polygenic risk scores (PRS), compared to average risk, ranges from 12 for testicular to 2.5 for ovarian cancer. We show that PRS have potential for risk stratification for cancers of breast, colon and prostate, but less so for others because of modest heritability and lower incidence.