The Gleason score

How it adds up

The Gleason score is used to help determine how quickly a tumor may grow or spread. It can be confusing because with the Gleason system (the most common system used), there’s both a “grade” and a “score."  We'll explain both for you.  

The Gleason grade uses numbers 1 to 5

A number is assigned to two of the areas of the prostate that have the most cancer, based on biopsy core samples that are taken. This is because the cancer may look different in each of those two areas.

Once those two numbers are determined, they are added together to come up with the Gleason score, which ranges from 2 to 10.

Two exceptions

  • If the highest grade takes up 95% or more of a man's biopsy, that grade is counted twice as the Gleason score
  • If three grades of cancer are found in one biopsy core sample, the highest grade is always used, even if the majority of the core sample involves low-grade cancer

Most biopsies are grade 3 or higher, according to the American Cancer Society.  Grades 1 and 2 are rarely used.

What the grades mean

  • Grade 1: The cells look almost like normal cells (called well differentiated) and are uniformly spaced in a tight mass.
  • Grade 2: The cancer cells are still well differentiated, but are arranged more loosely, are more irregular in shape, and some cells have spread to other prostatic tissue.
  • Grade 3: The cancer is moderately differentiated; cells vary in size from small to large; and more cells have invaded other prostatic tissue.
  • Grade 4: The cancer cells are irregular, distorted, and look less like normal cells (called poorly differentiated), and there is considerable spread (called invasion) to other prostatic tissue.
  • Grade 5: The cancer cells do not look anything like normal cells and have spread in haphazard “clumps” of all different shapes and sizes through the prostate.

What the Gleason scores mean

  • If the score is less than 6, the cancer may be considered to be well-differentiated or low-grade cancer
  • A score of 7 may be considered to be moderately differentiated or intermediate-grade cancer
  • A score of 8 to 10 may be considered to be poorly differentiated or high-grade cancer

After biopsy

According to the American Urological Association, the lowest Gleason score that is usually found after a biopsy is 5. The cancer is considered to be more aggressive as the score rises.

Scores of 8 to 10 are considered to be the most aggressive, which means that the cancer is more likely to grow and spread more quickly.

The biopsy results (called the pathology report) will contain other important information to help the doctor assess how aggressive prostate cancer may be. This includes:

  • How many biopsy core samples were positive for cancer
  • How much cancer was in each core sample (this is given as a percentage)
  • Whether cancer was found in just one side of the prostate gland or in both sides (which is referred to as bilateral)

When the score may change

The initial score is based on a man’s biopsy results, which only includes several small samples taken from the prostate.

If a man decides to undergo surgery to have his prostate removed (called radical prostatectomy), the entire prostate gland will then be examined. So his score may change after surgery.

Next: Prostate cancer staging

Disease 101
What is prostate cancer?
What are the causes?
Symptoms
PSA testing
Digital rectal exam
Diagnosis
Advanced cancer
Statistics

References:

The American Cancer Society. Prostate Cancer. http://www.cancer.org. Accessed March 17, 2015.

American Urological Association. The Management of Localized Prostate Cancer. http://www.auanet.org. Accessed March 20, 2012.

Walsh PC. Guide to Surviving Prostate Cancer. New York, NY: Time Warner Book Group; 2001.

Always consult a medical professional.

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