The cohort will include men who are enrolled in both Medicare Parts A and B for at least 1 year before the cohort entry date, have a primary site code of prostate cancer in SEER data, have surgical castration or androgen deprivation therapy after prostate cancer diagnosis, have evidence that prostate cancer was resistant to the castration as indicated by starting a second-line systemic therapy, and have an cohort entry date of 01 January 2006 or later on which they are aged 65 years or older. All eligible subjects will be selected; there will be no sampling. (The probability of selecting each eligible patient is equal to 1)