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Prostate Biopsy and the Gleason Score: What You Should Know

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Deciphering the Results

Biopsied tissue is sent to a laboratory, where a pathologist views the cells under a microscope. When healthy cells become cancerous, their appearance begins to change. The more altered the cells look, the more dangerous the cancer is likely to be.

The results from a prostate biopsy are usually given in the form of the Gleason score. On the simplest level, this scoring system assigns a number from 2 to 10 to describe how abnormal the cells appear under a microscope. A score of 2 to 4 means the cells still look very much like normal cells and pose little danger of spreading quickly. A score of 8 to 10 indicates that the cells have very few features of a normal cell and are likely to be aggressive. A score of 5 to 7 indicates intermediate risk.

A careful, detailed look at the biopsy results gives your doctor an even more precise picture of what’s happening in your prostate, says Michael Morris, MD, an oncologist at Memorial Sloan-Kettering Cancer Center in New York. For each biopsy sample, pathologists examine the most common tumor pattern and the second most common pattern. Each is given a grade of 1 to 5. These grades are then combined to create the Gleason score. For example, if the most common tumor pattern is grade 2, and the next most common tumor pattern is grade 3, the Gleason score is 2 plus 3, or 5. Because the first number represents the majority of abnormal cells in the biopsy sample, a 3 + 4 is considered less aggressive than a 4 + 3. Combined scores of 8 or higher are the most aggressive cancers. Those under 6 have a better prognosis.

It's important to remember that the Gleason score is assigned by a pathologist viewing cells under a microscope. Although the grading system has been shown to be reliable, it is not perfect. It depends on the skill of the pathologist observing the cells. For that reason, doctors may sometimes order a follow-up biopsy if they have any doubts or questions about the results.

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