CDK2 and breast cancer: In breast cancer cells, 1α,25 (OH) 2D3 has been found to inhibit tumor proliferation by binding to VDR, In ovarian cancer cells, 1,25 (OH) 2D3 upregulates p27 protein levels, inhibits cyclin E/CDK2 activity, leading to cell cycle arrest at G1 phase and suppression of proliferation (34).