The influence of vitamin D on mammographic density: results from CALGB 70806 (Alliance) a randomized clinical trial.

Current therapies for breast cancer prevention only prevent estrogen receptor positive (Er+) disease and toxicity limits use of these agents. Vitamin D is a potential prevention therapy for both Er+ and Er- disease and is safe with few side effects. This study evaluates the effect of one-year of vitamin D supplementation on mammographic density (MD), a biomarker of breast cancer risk in a multicenter randomized controlled trial. Premenopausal women with > 25% MD and no history of cancer, were randomly assigned to 2000IU of vitamin D or placebo orally daily for 1-year. Change in percent MD was evaluated using Cumulus software after all participants completed treatment. Three hundred women enrolled between 1/2011 and 12/2013 with a mean age of 43 and diverse ethnicity (14% Hispanic, 12% African American [AA]). Supplementation significantly increased vitamin D levels compared to placebo (14.5 ng/mL vs -1.6 ng/mL; p 50% MD and AA women, although neither reached significance. This randomized controlled trial demonstrated significant improvement in vitamin D levels with 2000 IU for one year, with 100% of supplemented women achieving sufficiency. However, a null effect was seen regarding change in MD for premenopausal women (the primary outcome of the study).