Abstract P3-12-03: Pre-diagnostic plasma 25-hydroxyvitamin D and mortality among women with breast cancer in the nurses’ health study cohorts

Abstract

Abstract Background: Sufficient levels of vitamin D are critical for optimal health. 25-hydroxyvitamin D (25(OH)D) is an essential steroid hormone, derived from sun exposure, diet, and supplement use, that is hypothesized to influence breast cancer prognosis by inhibiting breast tumor growth. While this has been observed in laboratory-based studies, findings from observational studies are inconclusive. We examined the association between pre-diagnostic 25(OH)D concentrations and both breast cancer-specific and overall mortality to explore the potential effects of vitamin D, a modifiable exposure. Methods: We evaluated the association between pre-diagnostic plasma 25(OH)D concentrations and breast cancer-specific and total mortality among 1,300 women diagnosed with invasive, non-metastatic breast cancer enrolled in the Nurses’ Health Study 1 (NHS1) and Nurses’ Health Study 2 (NHS2) cohorts. In this analysis, women provided a blood sample from 1989-1990 and a second blood sample in 2000-2001 (NHS1) or a blood sample from 1996-1999 (NHS2). Women were diagnosed with breast cancer after blood collection up through 2016 (NHS1) and 2017 (NHS2) and censored at end of study (2016 NHS1; 2017 NHS2) or death, whichever came first. Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (95%CI) for mortality after adjustment for tumor characteristics, type of cancer treatment, and lifestyle factors. For women with two blood samples, most recent exposure status was used in the analyses. Results: A total of 396 total deaths and 145 breast cancer-specific deaths occurred during follow-up through 2017. We observed a non-statistically significant 25% lower breast cancer-specific mortality rate among those with the highest, versus lowest, quartile of pre-diagnostic 25(OH)D levels (HRQ4vsQ1 0.75, 95%CI 0.45-1.25; p for trend=0.32), that did not vary significantly by estrogen receptor status of the tumor (p for interaction=0.61). Women in the highest vs. lowest quartile of plasma 25(OH)D experienced a 31% lower overall mortality rate (HRQ4vsQ1 0.69, 95%CI 0.51-0.93; p for trend=0.03). In cause-specific mortality analyses among non-breast cancer deaths, non-statistically significant decreases were observed for other cancer deaths and cardiovascular disease deaths. Conclusion: Pre-diagnostic plasma 25(OH)D levels were not significantly associated with lower breast cancer-specific mortality among women with breast cancer. However, significant inverse associations were observed for total mortality, which supports a potential benefit of vitamin D among these women. Citation Format: Etienne Holder. Pre-diagnostic plasma 25-hydroxyvitamin D and mortality among women with breast cancer in the nurses’ health study cohorts [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-12-03.