INTRODUCTION: Serum vitamin D levels measured as 25-hydroxyvitamin D have been shown to be low in cancer patients, including breast cancer patients. However, the vitamin D status has yet to be studied in different breast cancer phenotypes: luminal A, luminal B, HER2+/ER-, and triple negative comprising the majority of basal-like. CASE

PRESENTATION: Fifteen triple-negative breast cancer patients have presented to our medical oncology office in the last five years. Thirteen of these fifteen patients (87%) were found to be vitamin D deficient, defined as serum 25(OH)D less than 80 nmol/L, prior to initiation of adjuvant therapy. Ninety-one breast cancer patients from our office were classified as: luminal A (ER+ &/or PR+ and HER2-), luminal B (ER+ &/or PR+ and HER2+), HER2+/ER- (ER-, PR-, and HER2+), and triple-negative or basal-like (ER-, PR-, and HER2-). A normal mean was found from 78 volunteers. The breast cancer patients were found to be statistically different than the normal population. The triple-negative phenotype was found to be the most statistically different than the normal population.

CONCLUSION: The triple-negative breast cancer phenotype has the lowest average vitamin D level and the highest percentage of patients that are vitamin D deficient. These data suggests that low vitamin D levels are characteristic of the triple-negative phenotype.

Keywords: breast cancer, triple negative phenotype - vitamin d, 25(oh)d