The main cause of failure in chemotherapy treatments is that tumors develop resistance to anticancer drugs. Now, a new study reveals how vitamin D can help to overcome this problem. Using cultured tumor cells, scientists found an 'active metabolite of vitamin D3' that kills cancer cells. Researchers from South Dakota State University, in Brookings, have demonstrated that calcitriol and calcipotriol, two active forms of vitamin D, can block a mechanism that enables cancer cell