Some of the common downstream targets of 1,25(OH)2D3 signaling in breast cancer cells include BRCA1, p21, p53, cMYC, E-Cadherin, and Cyclin D1, which contribute to cell cycle arrest, differentiation, and, at times, apoptosis [20,52,64,65]. The gene discussed is CDKN1A; the disease is breast carcinoma.