If the prostate specific antigen test or the digital rectal examination results suggest prostate cancer, the doctor is likely to order a core needle biopsy.

A fine needle about the size used to draw blood, guided by ultrasound or a finger, is inserted through the rectum into the prostate, and samples of tissues are taken from nodules or from the entire prostate gland.

Several biopsy samples are removed from different areas of the prostate. Usually six to 18 core samples comprise the sample, and indicate whether -- and how much of -- the gland is affected by cancer.

A pathologist studies the tissue samples under a microscope in a laboratory and classifies the cells based on their relationship to normal cells.

If the pathologist finds cells that are abnormal, he or she picks two samples and ranks them to come up with a Gleason Score. The higher the score, the more likely your doctor is to recommend aggressive treatment.

A biopsy is more than 90 percent accurate in diagnosing prostate cancer, although occasional false-negative results occur when a small cancer in the gland is not sampled.