As prostate cancer disease progresses, the tumor can invade the prostate gland, the prostate envelope, and even reach the fatty layer outside the prostate envelope. Because the prostate is located in the lower posterior part of the bladder, prostate cancer can invade the base of the bladder. It can also spread to the pelvic muscles, the rectum behind the prostate, and even the lateral wall of the pelvis. When the cancer appears in a location other than the prostate, it is called metastasis. When prostate cancer tissue breaks through the prostate envelope and extra-envelope fat, the tumor often invades two important areas of the body: the lymph nodes that drain the prostate area and the bones. Lymph node metastases mainly involve metastases in the pelvic lymph nodes, and the bones that often metastasize are the spine and ribs. Prostate cancer rarely metastasizes to the abdominal parenchymal organs such as the liver.