The prostate is a walnut-sized gland located just below the bladder in men. It surrounds the top portion of the male urethra (the tube that transports urine and semen out of the body). The gland's main function is to produce semen (a thick fluid that nourishes and transports sperm). Prostate cancer (an abnormal, uncontrolled growth of cells originating in the prostate gland) is the most common cancer, and the third-leading cause of cancer deaths, among American men. About 1 man in 6 will be diagnosed with prostate cancer during his lifetime. Although about 80% of men who reach age 80 are found to have prostate cancer, this condition alone may not contribute to serious harm if it does not spread. The November 15, 2006, theme issue of JAMA on men's health includes several articles dealing with prostate cancer.