One theory is that vitamin D interferes with the effect of the androgen receptor, which is stimulated by hormones such as testosterone and implicated in prostate cancer.

BBC: Vitamin D hope in prostate cancer

Scouring patent databases, Dr. Jung discovered a compound made by the former French drug maker Roussel Uclaf that locked onto the androgen receptor about 100 times more strongly than the commonly used prostate-cancer drug, Casodex.

WSJ: New Medical Strides Against Prostate Cancer