Abstract 4126: The association of serum 25-hydroxyvitamin D with breast cancer characteristics and prognosis in the Pathways Study

Background: Vitamin D may be protective against breast cancer (BC), yet current evidence from epidemiologic studies is inconsistent. We previously reported lowest serum 25-hydyroxyvitamin D (25OHD) levels in premenopausal women with the triple-negative (TN) subtype. We aimed to validate our findings in an independent cohort and to further investigate 25OHD levels in association with breast cancer prognosis. Methods: Using a case-cohort design, 1664 invasive breast cancer patients were selected from the Pathways Study, a prospective cohort at Kaiser Permanente Northern California (KPNC). 25OHD levels were measured by immunochemiluminometric assay in blood samples collected close to diagnosis. Demographic and lifestyle information at baseline came from in-person interviews, and information on cancer characteristics, treatment, recurrence and death were obtained from KPNC cancer registries and clinical databases. We examined quartiles of 25OHD in association with BC characteristics (stage, grade, estrogen receptor status, TN subtype) using logistic regression, and with disease-free survival (DFS) and overall survival (OS) using Cox proportional hazards regression with covariate adjustment. Pending analyses will account for sampling in which biospecimens from all minorities, all non-Lum A subtypes (Lum B/TN/HER2-overexpressing), and a subset (30%) of white Lum A subtypes were selected. Results: Blood collection in winter-spring, younger age, obesity, black or Hispanic race/ethnicity, current smoking, low moderate-vigorous physical activity, no vitamin D supplement use, and low dietary vitamin D intake were associated with low serum 25OHD levels. In premenopausal women, 25OHD levels were associated inversely with cancer stage and grade, and those with the TN subtype had the lowest levels (Q4: adjusted OR vs. Lum A=0.41, 95% CI=0.19-0.86). Among white women after a median follow-up time of 5.9 y (range 2.5-7.8 y), high 25OHD levels were associated with longer DFS (Q4: adjusted HR=0.67, 95% CI=0.45-0.98), as well as OS (Q4: adjusted HR=0.58, 95% CI=0.36-0.92). Additional adjustment for stage, grade, subtype and treatment received had minimal effects on the above associations. The associations with DFS and OS appeared stronger in premenopausal women than in postmenopausal women. Conclusion: In a large prospective cohort of breast cancer patients, we validated our previous findings of 25OHD levels being associated with lower odds of TN tumor subtype in premenopausal patients. Moreover, preliminary results indicate that high 25OHD levels at the time of diagnosis were associated with longer DFS and OS, the relationships were independent of cancer characteristics and treatment, and may be stronger in premenopausal women. These findings support potential benefits of maintaining sufficient vitamin D levels for improved breast cancer prognosis. Citation Format: Song Yao, Chi-Chen Hong, Marilyn L. Kwan, Ting-Yuan Cheng, Li Tang, Susan E. McCann, Isaac J. Ergas, Janise M. Roh, Warren Davis, Christine B. Ambrosone, Lawrence H. Kushi. The association of serum 25-hydroxyvitamin D with breast cancer characteristics and prognosis in the Pathways Study. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4126. doi:10.1158/1538-7445.AM2014-4126