Despite theoretical benefits of intermittent as compared with continuous androgen-deprivation therapy in patients with metastatic prostate cancer, intermittent therapy did not result in longer survival or long-term improvement in quality of life. Prostate cancer is an androgen-dependent disease, and continuous androgen deprivation has been the standard therapy for metastatic hormone-sensitive disease. Despite a high response rate, resistance to androgen-deprivation therapy occurs in most patients, resulting in a median survival of 2.5 to 3 years. 1 , 2 There is evidence suggesting that progression to castration resistance is adaptive in part, and pathways involving the androgen receptor, as well as cell-survival pathways independent of the androgen receptor, have been implicated. 3 , 4 Data from an androgen-dependent tumor model have suggested that androgen withdrawal alters the ratio of putative stem cells in the tumor-cell population. 5 Initially, differentiated . . .