Vitamin D (VD) supplementation has pleiotropic effects that extend beyond their impact on bone health, including the disruption of downstream VD receptor signaling and human epidermal growth factor receptor 2 (HER2) signaling through the ErbB2/AKT/ERK pathway. In the present study, we examined our institutional experience with patients having nonmetastatic HER2-positive (HER(+)) breast cancer and hypothesized that those patients who received VD supplementation during neoadjuvant chemotherapy would have improved long-term outcomes.

We performed a retrospective review of all patients (n = 308) given trastuzumab-based chemotherapy between 2006 and 2012 at the University of Miami/Sylvester Comprehensive Cancer Center (UM/SCCC). We identified 2 groups of patients for comparison-those who received VD supplementation during neoadjuvant chemotherapy (n = 134) and those who did not (n = 112). Univariate and multivariate Cox proportional hazard regression models were fitted to overall survival (OS) and disease-free survival (DFS).

More than half of the patients received VD during neoadjuvant chemotherapy (54.5%), with 60% receiving a dose < 10,000 units/wk and 33.3% having a VD deficiency at the start of therapy. In our final multivariate model, VD use was associated with improved DFS (hazard ratio [HR], 0.36; 95% confidence interval [CI], 0.15-0.88; P = .026], whereas larger tumor size was associated with worse DFS (HR, 3.52; 95% CI, 1.06-11.66; P = .04). There were no differences in OS based on any of the categories, including VD use, tumor size, number of metastatic lymph nodes, age at diagnosis, or lymphovascular invasion (LVI).

VD supplementation in patients with nonmetastatic HER2(+) breast cancer is associated with improved DFS.