When a PSA blood test or digital rectal exam to screen for prostate cancer results in an abnormal finding, a prostate biopsy is performed to retrieve tissue samples from the prostate gland for closer examination by a pathologist. The procedure involves placing a narrow ultrasound probe into the rectum to provide image guidance (transrectal ultrasonography) that helps the urologist to pinpoint the appropriate location(s) to inject a numbing agent followed by the biopsy needle. Usually, 10 to 12 tissue samples are taken during the procedure, which only lasts about 10 minutes. These samples may be taken from more than one location in the prostate. Each time the needle extracts a sample, the patient may feel a brief amount of discomfort.