Prognostic effects of 25-hydroxyvitamin D serum concentrations in postmenopausal breast cancer

Background: Vitamin D has been inconsistently associated with breast cancer risk. Thus far, only one study has investigated its association with mortality after breast cancer diagnosis. We examined post-diagnostic serum concentrations of 25-hydroxyvitamin D [25(OH)D] in relation to all-cause mortality in postmenopausal breast cancer patients. Methods: Incident breast cancer patients aged 50–74 years were diagnosed between August 2002 and July 2005 and part of a population-based case-control study conducted in Germany (MARIE). Vital status was ascertained via local population registries up to the end of 2009, and deaths were verified by death certificates. For this analysis, we included 1,369 postmenopausal primary breast cancer cases with serum concentrations of 25(OH)D measured after diagnosis (median 83 days) and with information on tumor stage and personal history of other cancers. Cox proportional hazards regression stratified by age at diagnosis and season of blood draw was used to estimate univariate and multivariate risks of all-cause mortality. Results: Median follow-up time was 5.8 years (range 0.3 to 7.4 years), and 196 women died. Compared with the lowest category (<30 nmol/L), univariate hazard ratios (HR) and 95% confidence intervals (CI) for the higher categories of 25(OH)D serum concentrations (30–45, 45–60, 60–75 and ≥75 nmol/L) were 0.48 (0.32–0.71), 0.40 (0.26–0.63), 0.42 (0.25–0.70), and 0.38 (0.22–0.66), respectively (p-trend=0.0002). The association remained after multivariate adjustment for tumor stage, personal history of other cancers and diabetes, i.e. 0.60 (0.39–0.92), 0.55 (0.34–0.90), 0.50 (0.28–0.88), and 0.51 (0.28–0.93), respectively (p-trend=0.01). Further adjustment for therapy, ER/PR status, and several lifestyle factors did not substantially change the risk estimates. Associations were only statistically significant for women with blood drawn within 83 days of diagnosis (p-interaction <0.01) and for non-users of hormone replacement therapy (p-interaction <0.01). Conclusion: Higher serum 25(OH)D concentrations may be associated with improved overall survival in postmenopausal breast cancer patients.