Although vitamin D inhibits breast tumor growth and development in experimental settings, the findings from population-based studies remain inconclusive. Our goals were to investigate the association between prediagnostic plasma 25-hydroxyvitamin D [25(OH)D] concentration and breast cancer recurrence in prospective epidemiologic studies and to explore the molecular underpinnings linking 25(OH)D to slower progression of breast cancer. Our study included 659 women with invasive breast cancer from the Nurses’ Health Studies (NHS) diagnosed from 1989 to 2010. Plasma 25(OH)D was measured with a high-affinity protein binding assay or a radioimmunoassay. We profiled transcriptome-wide gene expression in breast tumors using microarrays. Hazard ratios (HRs) of breast cancer recurrence were estimated from covariate-adjusted Cox proportional hazards models. We examined differential gene expression regulation in association with 25(OH)D with covariate-adjusted linear regression and employed pathway analysis. We derived a gene expression score for 25(OH)D, and further assessed associations between the standardized score and breast cancer recurrence. Although 25(OH)D was not associated with breast cancer recurrence overall (hazard ratio (HR)=0.96; 95% confidence interval (CI): 0.86, 1.08) (median follow-up=12.8 years), the association varied by estrogen receptor (ER) status (p for interaction=0.005). Importantly, among ER-positive stage I to III cancers, every 5 ng/ml increase in prediagnostic plasma 25(OH)D was associated with a 13% lowered risk of recurrence (HR=0.87; 95% CI: 0.76; 0.99). No association was observed in women with stage I to III ER-negative cancers (HR=1.07; 95% CI: 0.91; 1.27). Pathway analysis identified multiple gene sets that were significantly (FDR<5%) downregulated in ER-positive breast tumors of women with high prediagnostic 25(OH)D (≥30 ng/ml), compared to those with low levels (<30 ng/ml). These gene sets are primarily involved in tumor proliferation, apoptosis, migration and invasion, inflammation, and cancer cell metabolism. The standardized score of 25(OH)D signatures derived from these gene sets was marginally significantly associated with reduced risk of recurrence in ER-positive diseases (HR=0.77; 95% CI: 0.59, 1.01). Using TIMER, a mathematical algorithm to deconvolute tumor cellular heterogeneity, we found more infiltrated CD8+ T cells in ER-negative tumors as compared to ER-positive tumors, and this higher immune infiltration in ER-negative tumors may contribute to the observed heterogeneous response. Our findings support an intriguing line of research for future studies to better understand the biologic mechanisms underlying the role of vitamin D in breast tumor progression, particularly for the ER-positive subtype.

Citation Format: Yujing Heng, Donghao Lu, Natalie DuPre, Kimberly Glass, Peter Kraft, David Feldman, Susan Hankinson, Kathryn Rexrode, Heather Eliassen, Rulla Tamimi, Cheng Peng. Prediagnostic 25-hydroxyvitamin D concentrations in relation to tumor molecular alterations and risk of breast cancer recurrence [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A85.