Abstract 2776: Prostate cancer and dietary calcium: Effect modification by the vitamin D receptor Cdx-2 polymorphism in the California Collaborative Prostate Cancer Study

Abstract

Abstract Background: Calcium is classified as a probable cause of prostate cancer by the World Cancer Research Fund. We previously showed that the relationship between dietary calcium intake and prostate cancer risk was modified by a the vitamin D receptor, Cdx-2 polymorphism among African Americans. The high absorption A allele increases calcium absorption and is common among African Americans. The A alleles is less common among Caucasians, who have a lower incidence of prostate cancer compared to African Americans. Methods: We examined Caucasian and African American prostate cancer cases and controls from the California Collaborative Prostate Cancer Study. Of 1854 cases, 1140 were advanced stage at diagnosis and 714 were localized; 500 were African American and 1354 were Caucasian. Dietary calcium was assessed from a 74-item modified Block food frequency questionnaire. The VDR Cdx-2 genotype was measured by TaqMan assay. Main effects of genotype and of dietary calcium, and diet-gene interactions were estimated using conditional logistic regression, adjusting for study site (Northern/Southern California), Hispanic ancestry, socio-economic status, age, and family history of prostate cancer. Results: Analysis of race-specific quartiles of calcium intake showed that intake of more than 680 mg/day (above the median for African Americans or above the first quartile for whites) was associated with increased prostate cancer risk (odds ratio 1.48, 95% confidence interval 1.25 – 1.77). The effect of calcium intake on risk of advanced (but not localized) prostate cancer was modified by the VDR Cdx-2 genotype for both African Americans and whites. High calcium intake (>680 mg/day) was significantly associated with increased risk only among those with the VDR Cdx-2 GG low calcium absorption genotype (OR=1.90, 95% CI 1.40 – 2.57). High absorption genotypes (GA and AA) were associated with increased risk only among those consuming less than 680 mg/day of calcium. Odds ratios were 1.24 (95% CI: 0.82 – 1.87) for genotype GA and 1.69 (95% CI: 1.05 – 2.74) for genotype AA compared to genotype GG. Conclusions: Our findings suggest that genetically-determined high calcium absorption among African Americans could contribute to racial ethnic disparities in prostate cancer incidence. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2776. doi:10.1158/1538-7445.AM2011-2776