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Background: Vitamin D and its metabolites are believed to impede carcinogenesis by stimulating cell differentiation, inhibiting cell proliferation, and inducing apoptosis. Certain pesticides have been shown to deregulate vitamin D's anticarcinogenic properties. We hypothesize that certain pesticides may be linked to prostate cancer via an interaction with vitamin D genetic variants.

Methods: We evaluated interactions between 41 pesticides and 152 single-nucleotide polymorphisms (SNP) in nine vitamin D pathway genes among 776 prostate cancer cases and 1,444 male controls in a nested case-control study of Caucasian pesticide applicators within the Agricultural Health Study. We assessed P-interaction values using likelihood ratio tests from unconditional logistic regression and a false discovery rate (FDR) to account for multiple comparisons.

Results: Five significant interactions (P < 0.01) displayed a monotonic increase in prostate cancer risk with individual pesticide use in one genotype and no association in the other. These interactions involved parathion and terbufos use and three vitamin D genes (VDR, RXRB, and GC). The exposure-response pattern among participants with increasing parathion use with the homozygous CC genotype for GC rs7041 compared with unexposed participants was noteworthy [low vs. no exposure: OR, 2.58, 95% confidence interval (CI), 1.07-6.25; high vs. no exposure: OR, 3.09, 95% CI, 1.10-8.68; P-interaction = 3.8 x 10(-3)].

Conclusions: In this study, genetic variations in vitamin D pathway genes, particularly GC rs7041, an SNP previously linked to lower circulating vitamin D levels, modified pesticide associations with prostate cancer risk.

Impact: Because our study is the first to examine this relationship, additional studies are needed to rule out chance findings. (C) 2013 AACR.