Breast cancer is a leading cause of cancer death in women, it is estimated that 42,240 women will die from cancer in 2024. MCF-7 is a breast cancer cell line that is estrogen-positive and has estrogen and progesterone receptors while MDA-MB-231 is a cell line that is triple-negative and lacks estrogen and progesterone receptors. Cholecalciferol (vitamin D3) is a pro-hormone with numerous health benefits. Individuals with higher Vitamin D levels have been found to have improved breast cancer survival rates. The ability of Vitamin D to improve the effectiveness of the chemotherapy Paclitaxel will be measured using an Alamar Blue assay to track cell survival.