ERBB2 and breast carcinoma: A retrospective study, which included a total of 308 breast cancer patients on Trastuzumab chemotherapy, showed that supplementation of <10,000 IU/week of vitamin D along with Trastuzumab improved the disease-free survival rate in HER2+ non-metastatic breast cancer patients when compared to those patients who did not receive the weekly vitamin D dosage [58].