Abstract 6428: Changes in mammographic features and breast tissue gene expression associated with vitamin D supplementation

Abstract Introduction: Experimental studies have shown anti-carcinogenic properties of vitamin D, but meta-analyses of randomized trials of vitamin D supplementation show reduction in cancer mortality but not cancer incidence. This study evaluated the effects of randomized moderate-dose vitamin D3 supplementation on mammographic features associated with breast cancer, and gene expression pathways in breast tumors. Methods: As part of an ancillary study to the VITamin D and OmegA-3 TriaL (VITAL) trial, we collected digital mammograms from women ≥ 55 years old, randomized in a 2X2 factorial design to vitamin D3 supplementation (2, 000 IU/day of cholecalciferol; n = 1317) or placebo (n = 1280). Digital mammograms were collected prior to randomization, and at 1, 3, and 4 years post randomization. Formalin fixed paraffin embedded tissue tumor blocks were collected for women who reported breast cancer post-randomization. RNASeq data were obtained from 25 tumors in the vitamin D arm and 21 from the placebo arm. The primary outcomes were (a) changes in percent mammographic density (PMD), and V, a mammographic feature that captures gray-scale pixel variation, and (b) tumor gene-expression patterns. A gene expression-based vitamin D score was developed in VITAL and evaluated in 3 independent data sets (Nurses’ Health Studies, TCGA, METABRIC) to determine if it was associated with long-term survival. Results: The mean age at randomization was 64 years of age; 27% of women self-reported their race as Black and 71% White. Both arms experienced significant declines in PMD and V from baseline to year 4. For PMD, those in the vitamin D arm had a 19.6% decline vs. 18.1% in the placebo arm (p=0.41 for difference between arms). For V, those in the vitamin D arm had a 6.5% decline compared with 4.0% in the placebo arm (p=0.02). There was a significant p-trend in the net effect of vitamin D3 over time for V (p=0.01). However, after adjustment for time-varying BMI the net effect was attenuated (p=0.11).Tumors in the vitamin D arm demonstrated down-regulation of multiple cancer related pathways (FDR ≤0.05), including proliferation and inflammation. The vitamin D gene expression score was associated with improved prognosis among stage I to III breast cancer cases in TCGA (p-trend=0.07), METABRIC (p-trend=0.005), and NHS (p-trend=0.04). Conclusions: Overall, randomized moderate dose vitamin D did not have a significant effect on PMD. Vitamin D had a stronger impact on V compared with placebo that appeared to be mediated through changes in BMI. Pathway analyses suggested that supplementation may have an important effect on breast cancer survival, consistent with the reduction in advanced cancers observed in VITAL. In conclusion, there was evidence that vitamin D impacted changes in breast tissue architecture on mammograms and influenced gene-expression patterns that were associated with improved breast cancer prognosis. Citation Format: Rulla M. Tamimi, Franco Giulianini, Cheng Peng, Nancy Cook, Yujin Heng, Vanessa Bret-Mounet, Liza Quintana, Julie Buring, JoAnn Manson, Erin Fowler, John Heine, Kathryn Rexrode. Changes in mammographic features and breast tissue gene expression associated with vitamin D supplementation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6428.