Free PSA antibodies as diagnostics, prognostics and therapeutics for prostate cancer

A method of monitoring fPSA levels in a subject with a prostate tumor, thereby monitoring a response to prostate cancer treatment, the method comprising:

• administering an antibody polypeptide that binds to an epitope of fPSA to a subject who had previously received a prostate cancer treatment;
• wherein the antibody polypeptide includes a detection entity;
• detecting the administered antibody polypeptide in situ in the subject by identifying the detection entity, thereby determining a first post-treatment level of fPSA in the prostate tumor or tissue of the subject;
• and
• comparing the first post-treatment level in the tumor or tissue with a pretreatment level of fPSA in the tumor or tissue of the subject, wherein a decrease in the first post-treatment level of fPSA when compared to the pretreatment level of fPSA is indicative that the treatment is effective;
• wherein the antibody polypeptide is 5A10, 4G10, or an antigen-binding fragment thereof.