Prostate cancer is a type of cancer that affects the prostate gland, which is part of the male reproductive system. The prostate gland is a small, walnut-sized gland located below the bladder and in front of the rectum. The most common type of prostate cancer is adenocarcinoma, which develops in the gland cells. Prostate cancer is usually slow-growing and may not cause any symptoms for many years. However, it can spread to other parts of the body if left untreated.