Prostate cancer occurs when some of the cells in the prostate reproduce far more rapidly than normal, resulting in a tumor. Prostate cancer often grows slowly to start with and may never cause any problems. But some men have prostate cancer that is more likely to spread. These prostate cancer cells, if left untreated, may spread from the prostate and invade distant parts of the body, particularly the lymph nodes and bones, producing secondary tumors in a process known as metastasis.