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Prostate Biopsy and the Gleason Score: What You Should Know

Deciphering the Results continued...

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.

Understanding the Gleason Score

The Gleason score is only one piece of information that you and your doctor will use. Biopsy reports also typically include the number of biopsy core samples that contain cancer, the percentage of cancer in each of the cores, and whether the cancer occurs on one side or both sides of the prostate. The farther the cancer has spread, the more risk it poses. Researchers have developed a number of different tools that help doctors come up with the best prediction of the aggressiveness of the cancer they found.

"Prostate cancer is really a spectrum of diseases,” says Howard I. Scher, MD, chief of genitourinary oncology at Memorial Sloan-Kettering Cancer Center. “The type of tumor, the Gleason grade, and the extent of the disease varies widely among patients.” Along with biopsy results, your doctor will weigh the results from your PSA test, a digital rectal exam, and perhaps images from ultrasound or CAT scans.

To make sense of so many variables, doctors use a staging system, based on how much cancer is present and how far it has spread. Stage I, also called T1, describes when tumor cells are found in less than 5% of prostate tissue and the cells are low-grade. Stage II (T2) describes more extensive or more aggressive cells that are confined to the prostate. In stage III, or T3, the tumor has grown through the capsule that contains the prostate. In Stage IV (T4), the cancer has spread beyond the prostate to other organs.

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