Abstract Vitamin D is hypothesized to decrease breast cancer risk by controlling cell proliferation, differentiation and apoptosis, and estrogen synthesis and signalling in breast tissue. Transport of circulating vitamin D to sites of action is facilitated by vitamin D binding protein, encoded by the GC gene, whereupon it binds to the vitamin D receptor, encoded by the VDR gene. Given that polymorphisms in the GC and VDR gene have not been consistently associated with breast cancer risk, our objective was to assess the associations of vitamin D-related genes with breast cancer risk, accounting for ethnicity and menopausal status, and to determine these associations according to tumour receptor status defined by expression of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor-2 (HER2). A case-control study of 1,037 breast cancer cases and 1,050 controls age-frequency matched in Vancouver, British Columbia and Kingston, Ontario was used. The distribution and associations of 21 single nucleotide polymorphisms (SNPs) of the GC and VDR gene with breast cancer risk and breast tumour subtypes were investigated among premenopausal and postmenopausal European and Asian women in stratified analyses. Following false discovery rate adjustment, no SNP was associated with breast cancer risk among any subgroup. However, among European women, two SNPs in the VDR gene, rs1544410 (OR = 0.38, 95% CI: 0.21 - 0.70) and rs7967152 (OR = 2.80, 95% CI: 1.62 - 4.85) were associated with risk of ER-/PR-/HER2+ breast tumour subtype, but not with other breast tumour subtypes. Breast tumour subtypes are proposed to be etiologically distinct disease states, with different risk factors and prognostic outcomes. Interactions between variations in vitamin D-related genes and breast tumour subtypes are biologically plausible given our current understanding of anticarcinogenic properties of vitamin D elicited through the regulation of cell growth and reproductive hormone synthesis. These findings provide additional insight into the etiologic differences among breast tumour subtypes. Citation Format: Joy Shi, Anne Grundy, Harriet Richardson, Angela Brooks-Wilson, John Spinelli, Kristan J. Aronson. Polymorphisms in vitamin D-related genes and risk of breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2792. doi:10.1158/1538-7445.AM2015-2792
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