Prostate Cancer: What You Need to Know About The Gleason Score
by Dr. C.H. Weaver M.D. updated 9/10/2018
How important is the Gleason score?
The Gleason score is currently the most useful tool for predicting the behavior of a prostate cancer and determining the best treatment options. It is used by your doctor in combination with the cancer stage and other variables to guide treatment decision making.
What is the Gleason Score?
The Gleason grading system estimates the “aggressiveness of the cancer” by assigning a pattern to the cancer cells depending on their appearance under the microscope. A number from 1 to 5 is used as a measure of how aggressive the cancer looks under the microscope.
- If the cancerous tissue looks much like normal prostate tissue, a grade of 1 is assigned.
- If the cancer cells and their growth patterns look very abnormal, a grade of 5 is assigned.
- Grades 2 through 4 have features in between these extremes.
The most common type of prostate biopsy is a core needle biopsy. For this procedure, the doctor inserts a thin, hollow needle into the prostate gland. When the needle is pulled out it removes a small cylinder of prostate tissue called a core. This is typically repeated several times to sample different areas of the prostate.
Since multiple core biopsy samples are evaluated and prostate cancers in a single patient often have areas with different grades the pathologist assigns two “grades” to the examined prostate tissue. The first “grade” is the most common pattern seen after review of all the biopsy specimens and the “2nd grade” is assigned to the next most common pattern.
The two different grades are then added together to create the Gleason score. For example, if the Gleason score is written as “3+5 = 8”, it means most of the cancer is primarily pattern 3 and to a lesser amount pattern 5. The two numbers are then added together to create a Gleason score of 8. The higher the Gleason score, the more likely it is that your cancer will grow and spread quickly.
Gleason Score and the Risk of Prostate Cancer Recurrence 5 Years Following Radical Prostatectomy
Gleason Score Risk of Recurrence
- 6 5%
- 3 + 4 = 7 (17% risk)
- 4 + 3 = 7 (35% risk)
- 4 + 4 = 8 (37% risk)
- 9 or 10 (76% risk)
In actual practice, the Gleason score ranges between 6 and 10. Therefore, a Gleason 6 represents the lowest grade (the most favorable) possible.
What do Gleason scores of 6, 7, 8, or 9-10 actually mean?
Because grades 1 and 2 are not often used for biopsies, the lowest Gleason score an individual can have is 6. Cancers with a Gleason of 6 are well differentiated or low-grade and are likely to be less aggressive.
Cancers with Gleason scores of 8 to 10 are more poorly differentiated or high-grade. These cancers are likely to grow and spread more quickly.
A Gleason score of 7 can be made up of either 3+4=7 or 4+3=7, depending on whether the pattern 3 or pattern 4 is predominant. There is a big difference between these two grades.
· Gleason score 3+4=7 tumors still have a good prognosis (outlook), although not as good as a Gleason score 6 tumor.
- A Gleason score 4+3=7 tumor is more likely to grow and spread than a 3+4=7 tumor, yet not as likely as a Gleason score 8 tumor.
What does it mean when there are different biopsy cores with different Gleason scores?
Different cores typically sample different areas of the same cancer, or the cores may sample different cancer in the prostate. Because the grade of a prostate cancer may vary different cores taken from the prostate may have different Gleason scores.
Can the Gleason score from a random biopsy really tell what the cancer grade is in the entire prostate?
The answer is yes because prostate biopsies are tissue samples from different areas of the prostate. However, in about 20% of individuals, the biopsy may underestimate the true grade because randomly directed biopsy needles occasionally miss a higher grade (more aggressive) area of the cancer. This “under-grading” is more likely to occur in men with larger tumors, higher PSA levels, and/or smaller prostates. “Over-grading” can also occur but is less common.
How do I know the Gleason grade is accurate?
Assigning the correct Gleason score is a skill just like any other that is developed through experience and practice. It is often prudent to have the biopsy material referred for a second opinion at a reference center to confirm the accuracy of the initial Gleason score that was assigned.
- Johns Hopkins. Prostate Cancer on Needle Biopsy. “The lowest Gleason score (least aggressive) tumor that is typically present on prostate biopsy is a 6 with higher grades (maximum Gleason score 10) corresponding to progressively more aggressive tumors.”