Prostate biopsy is considered to be the most definitive diagnostic tool for prostate cancer. It is a surgical procedure in which a small sample of tissue is removed from the prostate gland and examined by a pathologist. The procedure normally takes about 15 minutes and is usually performed by the urologist in conjunction with transrectal ultrasound (TRUS). No anesthetic is required. With the help of TRUS, a doctor guides a biopsy gun -- a hand-held device with a spring-loaded, slender needle -- through the wall of the rectum into the area of the prostate gland that appears abnormal. Since the rectal wall is thin, it is possible to place the needle more accurately and with less injury to other tissues. When activated, the needle can remove a slender cylinder of tissue, called a core.