Polygenic risk score as a determinant of risk of keratinocyte cancer in an Australian population-based cohort.

BACKGROUND: Keratinocyte cancer (KC) risk is determined by genetic and environmental factors. Genetic risk can be quantified by polygenic risk scores (PRS), which sum the combined effects of single nucleotide polymorphisms (SNPs). OBJECTIVES: Our objective here was to evaluate the contribution of the summed genetic score to predict the KC risk in the phenotypically well-characterized Nambour population. METHODS: We used PLINK v1.90 to calculate PRS for 432 cases, 566 controls, using 78 genome-wide independent SNPs that are associated with KC risk. We assessed the association between PRS and KC using logistic regression, stratifying the cohort into three risk groups (high 20%, intermediate 60%, low 20%). RESULTS: The fully adjusted model including traditional risk factors (phenotypic and sun exposure-related), showed a significant 50% increase in odds of KC per standard deviation of PRS (odds ratio (OR) = 1.51; 95% confidence interval (CI) = 1.30-1.76, P = 5.75 × 10-8 ). Those in the top 20% PRS had over three times the risk of KC of those in the lowest 20% (OR = 3.45; 95% CI = 2.18-5.50, P = 1.5 × 10-7 ) and higher absolute risk of KC per 100 person-years of 2.96 compared with 1.34. Area under the ROC curve increased from 0.72 to 0.74 on adding PRS to the fully adjusted model. CONCLUSIONS: These results show that PRS can enhance the prediction of KC above traditional risk factors.

Is there a causal relationship between vitamin D and melanoma risk? A Mendelian randomization study.

BACKGROUND: Several preclinical studies have identified the antiproliferative effects of 25-hydroxyvitamin D [25(OH)D; vitamin D]. Ultraviolet radiation (UVR) is essential for vitamin D synthesis yet increases the risk of melanoma. Observational studies on the association of vitamin D levels with melanoma risk have reported inconclusive results, and are difficult to interpret owing to the potential confounding from the dual role of UVR. OBJECTIVES: To determine whether there is a causal association between genetically predicted 25(OH)D concentrations and melanoma using a Mendelian randomization (MR) approach. METHODS: We performed MR using summary data from a large genome-wide association study (GWAS) meta-analysis of melanoma risk, consisting of 12 874 cases and 23 203 controls. Five single nucleotide polymorphisms associated with 25(OH)D concentration - rs12785878, rs10741657, rs2282679, rs6013897 and rs116970203 - were selected as instrumental variables. An inverse variance weighted method was used to access the evidence for causality. MR results from the melanoma meta-analysis were combined with results from an MR study based on a melanoma risk GWAS using UK Biobank data. RESULTS: A 20 nmol L-1 decrease in 25(OH)D was not associated with melanoma risk [odds ratio (OR) 1·06, 95% confidence interval (CI) 0·95-1·19]. Results from the UK Biobank were concordant with this, with meta-analysis of our and UK Biobank-derived MR causal estimates showing no association (OR 1·02, 95% CI 0·92-1·13 for a 20 nmol L-1 decrease). CONCLUSIONS: The results suggest that vitamin D levels may not be causally associated with the risk of melanoma. What's already known about this topic? Antitumour activity of vitamin D has been identified in preclinical studies. Observational studies link vitamin D deficiency with an increased risk of a range of cancers. There is a growing public interest for vitamin D supplementation. Observational studies of melanoma are fraught with difficulties because while higher ultraviolet radiation levels increase vitamin D levels, such exposure is also associated with increased melanoma risk. Results from observational studies are inconclusive regarding the effect of vitamin D on melanoma risk. What does this study add? Using Mendelian randomization, an approach to causal inference, which is analogous to a natural randomized controlled trial, we found no causal association between vitamin D levels and melanoma.