Prostate cancer is cancer that starts in the prostate gland, a small, walnut-sized structure that makes up part of a man's reproductive system. It wraps around the urethra, the tube that carries urine out of the body. Prostate cancer is the most common cause of death from cancer in men over age 75 and is rarely found in men younger than 40. People who are at higher risk include African-American men, who are also likely to develop cancer at every age; men who are older than 60; and men who have a father or brother with prostate cancer.