Metastasized prostate cancer is cancer that has spread to sites outside of the prostate, according to the National Cancer Institute. For example, in stage 3 prostate cancer, the cancer has spread into the seminal vesicles but hasn't spread to the lymph nodes or anywhere else, according to the American Cancer Society.
In one type of stage 4 cancer, the cancer has spread to nearby lymph nodes, the patient's bladder, rectum or areas in the pelvis, according to the American Cancer Society. In another type of stage 4 prostate cancer, the cancer has reached more distant sites in the patient's body.
The staging system for prostate cancer can be complex, according to the American Cancer Society. However, it provides fairly detailed information about the cancer for both the doctor and the patient. In the American Joint Committee on Cancer TNM system, "T" stands for the primary tumor, "N" stands for any lymph nodes that have been invaded by the tumor, and "M" stands for distant metastasis. The system also takes into account the patient's PSA levels and the Gleason score.
PSA stands for prostate-specific antigen, according to the American Cancer Society. A high PSA level can indicate a malignancy, and levels usually go down after treatment. The Gleason score grades a prostate tumor by examining it under a microscope, according to the National Cancer Institute.