The objectives of this study were to estimate the proportion of vitamin D deficiency among breast carcinoma patients and determine the association between vitamin D deficiency and tumor grade, histopathological subtype, and axillary lymph node status and their effect on the function of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (Her-2/neu). This evidence concerns the gene ESR1 and vitamin D deficiency.