The present invention provides methods of monitoring and measuring tumor-associated free PSA (“fPSA”) with antibody polypeptides as an indication of androgen receptor signaling. In a particular embodiment, the methods may be used to assess the efficacy of anti-androgen and/or general anti-cancer treatments. The present invention also provides various methods and compositions relating to antibodies that are specific for tumor-associated or intratumoral fPSA. For example, the present invention provides compositions, including pharmaceutical compositions, comprising anti-fPSA antibodies, or fragments or characteristic portions thereof. The present invention further provides various therapeutic and/or diagnostic methods of using anti-fPSA antibodies and/or compositions.