Patients who have been diagnosed by core biopsy with carcinoma in situ, ductal or lobular, will be evaluated for vitamin d supplementation. Patients with vitamin d levels less than 50 will be eligible for participation. They will receive a one month (30 days) schedule of vitamin D supplementation and then proceed with the standard of care of surgical excision. Immunohistochemistry studies will be performed on the diagnostic core biopsy and the surgical specimen to evaluate the impact of vitamin d supplementation on: the proliferative index-ki67, proliferative marker- PCNA, proteins of the autophagy pathway (LC3B, ATG7), her2 localization, and levels of PMCA2 - calcium efflux channel.