Abstract 2787: Circulating 25-hydroxyvitamin D and risk of endometrial cancer: Results from the Cohort Consortium Vitamin D Pooling Project of Rarer Cancers

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Abstract Objective: Experimental evidence suggests that vitamin D, a modifiable factor, protects against cancer. Ecological studies have reported an inverse association between ultraviolet B irradiation and endometrial cancer incidence rates, suggesting a protective role of vitamin D against endometrial cancer. The purpose of this study was to examine the association between circulating 25-hydroxyvitamin D (25(OH)D), the best indicator of vitamin D status, and risk of endometrial cancer within a large nested case-control study in the Cohort Consortium Vitamin D Pooling Project of Rarer Cancers (VDPP). Methods: The study included 830 cases and 992 matched controls from seven cohorts: CLUE, the Cancer Prevention Study II Nutrition Cohort (CPS-II), the Multiethnic Cohort Study (MEC), the Nurses’ Health Study (NHS), the New York University Women's Health Study (NYUWHS), the Prostate, Lung, Colorectal and Ovarian Cancer (PLCO) Study, and the Shanghai Women's Health Study (SWHS). Matching factors included cohort, age at blood donation, date of blood donation and race. Serum/plasma samples were assayed for 25(OH)D using the DiaSorin LIAISON 25(OH)D TOTAL assay, a direct, competitive chemiluminescence immunoassay. Conditional logistic regression was used in the main analysis using clinically-defined cutpoints corresponding to deficient, insufficient, and sufficient 25(OH)D concentrations with 50 to <75nmol/L as the reference category, as well as using season-specific cutpoints to take into account seasonal changes in 25(OH)D levels. Results: The median concentration of 25(OH)D was slightly lower in cases (49.4 nmol/L) than in controls (50.8 nmol/L, P = 0.08). In the crude analysis, there was some suggestion (P for trend = 0.12) that lower concentrations (<25 nmol/L) were associated with a small increased risk of endometrial cancer compared to the referent category of 50-<75 nmol/L (odds ratio (OR): 1.20; 95% confidence interval (CI): 0.83, 1.72) and higher concentrations (≥100 nmol/L) were associated with a lower risk (OR: 0.78; 95% CI: 0.45, 1.34). However, there was no association between 25(OH)D concentration and disease risk after adjusting for body mass index (BMI), which was strongly associated with both endometrial cancer risk and circulating 25(OH)D. Compared to the 50-<75 nmol/L 25(OH)D category, the BMI-adjusted OR and 95% CI were 1.08 (95% CI: 0.73, 1.57) for the <25 nmol/L category and 0.90 (95% CI: 0.51, 1.58) for the ≥100 nmol/L category (P for trend = 0.99). Null results were also observed after further adjustment for other risk factors, in stratified analyses and in analyses limited to women who did not use calcium supplements, white women, or women with endometrioid tumors. Conclusion: Although an effect of circulating 25(OH)D at high concentrations cannot be ruled out, these results do not support a protective role of vitamin D against endometrial cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2787.