Dark Green Leafy Vegetable Intake, MTHFR Genotype, and Risk of Cutaneous Squamous Cell Carcinoma

Background: Evidence suggests that consumption of dark green leafy vegetables may influence the decrease in the risk of cutaneous squamous cell carcinoma (SCC). Dark green leafy vegetables contain folate as a main component among other nutrients; thus, we hypothesised that their possible observed protective effect on SCC, observed in previous studies, would be more evident in persons with specific genotypes related to folate metabolism. Methods: Genotyping of methylenetetrahydrofolate reductase (MTHFR) gene variants rs1801133 (C677T) and rs1801131 (A1298C) was carried out for 1,128 participants in an Australian community-based longitudinal study of skin cancer. Dietary intakes were assessed through repeated Food Frequency Questionnaires (1992–1996), and all incident skin cancers were recorded in 1992–2007 and histologically confirmed. We assessed associations between intake of dark green leafy vegetables and SCC development in strata defined by genotype, by calculating relative risks (RRs) with 95% confidence intervals (CIs) using generalised linear models with negative binomial distribution and person-years of follow-up as offset. Results: High versus low intake of dark green leafy vegetables was associated with a lower risk of SCC tumours in carriers of the C677T variant allele (RR = 0.42, 95% CI = 0.23–0.75), and within wild-type A1298C homozygotes (RR = 0.43, 95% CI = 0.22–0.85). Conclusion: The protective effect of dark green leafy vegetables on cutaneous SCC may be genotype-dependent. Folate metabolism-related gene polymorphisms should be considered when assessing the relation of green leafy vegetables to cancer risk.