One important component of staging your cancer is the grade of the cancer. While the stage of your cancer looks at where the cancer is present in your body—how it is behaving at the macro level—the grade describes what the actual cancer cells look like under a microscope—how they are behaving on a micro level.
Traditionally, prostate cancer grades were described according to the Gleason Score, a system named for the pathologist who developed it in the 1960s. Dr. Donald Gleason realized that cancerous cells fall into 5 distinct patterns as they change from normal cells to tumor cells. The cells are graded on a scale of 1 to 5. Grade 1 cells resemble normal prostate tissue. Cells closest to 5 are considered “high-grade” and have mutated so much that they barely resemble normal cells.
How is the Gleason Score Derived?
The pathologist looking at the biopsy sample will assign one Gleason grade to the most predominant pattern in your biopsy and a second Gleason grade to the second most predominant pattern. For example: 3 + 4. The two grades will then be added together to determine your Gleason score. Theoretically, Gleason scores range from 2-10. However, since Dr. Gleason’s original classification, pathologists almost never assign scores 2-5, and Gleason scores assigned will range from 6 to 10, with 6 being the lowest grade cancer.
What Does it Mean?
A Gleason score of 6 is low grade, 7 is intermediate grade, and a score of 8 to 10 is high grade cancer.
It’s also important to know whether any cells rated at Gleason grade 5 are present, even in just a small amount, and most pathologists will report this. Having any Gleason grade 5 in your biopsy or prostate puts you at a higher risk of recurrence.
But because many prostate cancer cases are extremely slow-growing, the Gleason system didn’t necessarily do a good job of communicating the risks for these cases. Patients with scores of 6 and 7 didn’t have a clear picture of the nature of their particular cancer.
What is a Grade Group?
In 2014, the International Society of Urological Pathologists released supplementary guidance and a revised prostate cancer grading system, called the Grade Groups.
The Grade Group system is simpler, with just five grades, 1 through 5.
Low Grade: Group 1 = Gleason Score ≤ 6
Intermediate Favorable: Grade Group 2 = Gleason Score 7 (3 + 4)
Intermediate Unfavorable: Grade Group 3 = Gleason Score 7 (4 + 3)
High Grade: Group 4 = Gleason Score 8
Very HighGrade: Group 5 = Gleason Score 9-10
Many hospitals report both the Gleason score and the Grade Group, but there may be hospitals that still report only the old Gleason system.