You can participate in the decision making surrounding your cancer treatment, including whether or not surgery, which carries with it certain side effects, is right for you.

Anyone who has been faced with the prospect of prostate cancer will encounter the phrase “Gleason score.” And what is the Gleason score? Doctors use it to help them predict the risk of how aggressive a prostate cancer may be and how likely it is to spread beyond the prostate gland.

But let’s back up for a minute. When you undergo a biopsy of your prostate gland—whether it was prompted by suspicious symptoms, because your doctor felt something concerning during a digital rectal exam (DRE), or because you had an abnormal prostate-specific antigen (PSA) level—your urologist will usually take 10 to 12 small tissue samples from different areas of the prostate. These samples will be sent to a pathologist who will evaluate the cells in the tissue samples on a microscopic level, comparing them with normal prostate cells.

Most pathologists today will make this comparison using a grading system first created by pathologist Dr. Donald Gleason in the 1960s, aptly called the Gleason System. The Gleason System involves assigning a numerical value or grade, ranging from 1 to 5, to the predominant and next-most-predominant type or pattern of cells in each tissue sample. The numerical value—the Gleason score—reflects the architecture of the cells, in particular how differentiated the cells are. Well-differentiated cells are cells that are small, uniform in shape, fairly compactly grouped together, and whose borders are distinct.

Normal prostate cells are well differentiated. Poorly differentiated cells, representing the most aggressive cancer cells, are irregular in shape, size, and have borders that may be indistinguishable.

• Gleason Grade 1 represents cancer cells that are very well differentiated and most closely represent normal cells.
• Gleason Grade 5 represents cancer cells that are the most poorly differentiated.
• Gleason Grades 2 to 4 represent patterns of differentiation in between 1 and 5.

By the Numbers: What Is the Gleason Score?

Pathologists take the grade from the most common cell pattern and the next most common pattern in each sample and add them together to create the Gleason score (also called the Gleason sum). The score can range from 2 to 10, but the vast majority of scores fall within the 6 to 7 range. In fact, less than 2 percent of men have a score of 2 to 4.

The Gleason score can be reported one of several ways, depending on the pathologist’s preference. For example, a 7 may appear on your pathology report listing in any of the following ways:

• Gleason score 7
• Gleason score 7/10 (meaning it is a 7 out of a possible total of 10)
• Gleason score 7 (3 + 4) or Gleason score 7 (4 + 3)

The order of numbers in the parentheses of the latter form of the score is significant. The first number in the parentheses represents the predominant cell pattern, so if the 4 is listed before the 3, it means there were more of the less differentiated or grade 4 cells than there were of the grade 3 cells. Thus, even if the total score is the same, some doctors view the risk associated with that score differently depending on the breakdown of the two numbers added together to achieve that sum.

Gleason Score: What the Numbers Mean

In general, Gleason scores are viewed such that:

• Gleason scores of 2 to 4 are Low Risk
• Gleason scores of 5 to 7, if the 7 results from (3 + 4), are Moderate Risk
• Gleason score of 7, if the 7 results from (4 + 3), to 10 are High Risk

Your pathology report may list different Gleason scores for each tissue sample taken during the biopsy. The highest Gleason score among all of the samples, however, is the most important score. Your doctor will use the Gleason score in combination with a number of different factors to help determine your treatment and predict your prognosis (chance of recovery). These factors include your PSA level, how much of each tissue sample was comprised of cancer, the total number of samples that contained cancer, findings on DRE, and whether the cancer has spread beyond the prostate gland.

For related reading, please visit these posts:

• “Don’t Rush to Surgery for Prostate Cancer“
• “Prostate Cancer Survival Rate? Treatments That Increase Your Odds“
• “How to Avoid Prostate Cancer“

Originally published in 2016, this post is regularly updated.