Prostate cancer is now the most commonly diagnosed tumor among men in the United States. Most patients have tumors that are confined to the prostate gland at diagnosis and are suitable for treatment with surgery or radiotherapy (RT) that is aimed at curing the disease. Nevertheless, despite recent improvements in these treatments, a large number of men continue to die of prostate cancer. These patients often have spread of tumor to other areas of the body, and are treated with hormones that produce initial tumor shrinkage. However, over time the tumor learns to grow despite continued hormonal treatment. Effective therapy for patients with hormone-resistant prostate cancer is lacking and patients often deteriorate quickly and die. Thus, there is a need for better treatment that cures prostate cancer at an early stage, and a better understanding of the biology of prostate cancer specifically with respect to factors that determine the effectiveness of RT, the spread of tumor and the development of hormone-resistant disease.