What to know about the Gleason score
The Gleason score helps doctors determine how aggressive the cancer is and the best course of treatment for the patient.
In this article, we explain the Gleason score, what the results mean, and alternative techniques for assessing prostate cancer progression.
What is the Gleason score?
The Gleason score measures the progress of a cancer cell from normal to tumorous.
In the 1960s, a pathologist called Donald Gleason devised a grading system called the Gleason score.
Gleason worked out that cancerous cells fall into five different patterns as they change from normal cells to tumorous cells. As a result, he determined a scale of 1–5 that represents these changes.
Cells that score a 1 or 2 are low grade tumor cells. These usually look similar to healthy cells.
Cells closer to a score of 5 are high grade. By this point, they have mutated so much that they no longer look like regular cells.
Calculating the Gleason score
A doctor will use the results of a biopsy to calculate the Gleason score.
During a biopsy, a healthcare professional will take tissue samples from different areas of the prostate. The cancer is not always present in all parts of the prostate. For this reason, they will often collect several samples.
After examining the samples under a microscope, they will identify the two areas with the most cancer cells. They will then assign a score to each of these areas. Then, they will add these scores together to give a combined score, often referred to as the Gleason sum.
It is important to note that sometimes, a doctor will use a different method for calculating the Gleason score.
For example, when a biopsy sample has either a large number of high grade cancer cells or shows three different grades of mutation, they will modify the Gleason score to more accurately reflect how aggressive they deem the cancer to be.
A person's Gleason score can technically range from 2–10, but it is much more likely to range from 6–10. We will explain why this is in the sections below.
What do the results mean?
A higher Gleason score indicates more aggressive prostate cancer. Typically, lower scores suggest a less aggressive cancer.
In most cases, scores range between 6–10. Doctors do not often use biopsy samples that score 1 or 2, as they are not usually the predominant areas of the cancer.
A Gleason score of 6 tends to be the lowest possible score. A doctor will describe prostate cancer with a score of 6 as being "well differentiated," or low grade. This means that the cancer is more likely to have a slower rate of growth.
Scores in the 8–10 region are "poorly differentiated," or high grade. In these cases, the cancer is likely to spread and grow quickly. The growth rates of cancers with a score of 9 or 10 are likely to be twice as high as those of a cancer with a score of 8.
A score of 7 can be broken down in two ways:
- 3 + 4 = 7
- 4 + 3 = 7
This distinction indicates how aggressive the tumor is. Scores of 3 + 4 typically have a good outlook. A score of 4 + 3 is more likely to grow and spread than the 3 + 4 score, but less likely to grow and spread than a score of 8.
Some people receive multiple Gleason scores. This is because the grade may vary between samples of the same tumor or between two or more tumors.
In these cases, doctors are likely to use the higher score as the guide for treatment.
There are other factors which help determine the treatment plan for prostate cancer, including blood PSA levels and biopsy results.
The Gleason score is an important tool for doctors when deciding on the best course of treatment. However, additional factors and grouping systems can assist them in making this decision.
Some additional considerations include:
- the results of a rectal exam
- the level of prostate-specific antigen (PSA) in a blood test
- the results of imaging tests of the prostate
- the number of biopsy samples that contain cancer
- whether or not the cancer has spread beyond the prostate
- how much of each tissue sample consists of cancer
- whether or not the cancer has developed on both sides of the prostate
More recently, researchers have determined additional groupings called grade groups. These grade groups help address some of the problems with the Gleason score system.
For example, receiving a Gleason score of 6 leads some people to think that their cancer is in the middle of the grade scale, whereas in reality, this is a low score. As a result, they may worry and request immediate treatment.
In the original groupings, doctors divide Gleason scores into three groups: 6, 7, and 8–10. These groupings are not entirely accurate, since a Gleason score of 7 is made up of two grades: 3 + 4 and 4 + 3.
Also, Gleason scores of 9 or 10 have a worse outlook than a Gleason score of 8, despite being in the same group.
The newer grouping systems are clearer for the patient and more accurate in terms of outlook and treatment.
The groups and corresponding Gleason scores are as follows:
- Grade group 1: 6 or under
- Grade group 2: 3 + 4 = 7
- Grade group 3: 4 + 3 = 7
- Grade group 4: 8
- Grade group 5: 9–10
People with a Gleason score in grade group 1 have the best outlook. Those in group 5 have a poor outlook and will require a more intensive treatment plan.
Effect on treatment
More advanced cancers may be treated with surgery, radiation therapy, or chemotherapy.
Healthcare professionals use the Gleason score, plus other factors, to inform treatment decisions for a person with prostate cancer.
For lower Gleason scores, treatment is likely to consist of:
- active surveillance, during which the person's age and overall health help determine the timing of prostate cancer treatment
- radical prostatectomy, which is surgery to remove the prostate
- radiation therapy
For higher Gleason scores, treatment may consist of a combination of the following:
brachytherapy, a type of radiation therapy wherein healthcare professionals will place small radioactive seeds directly into the prostate
external beam radiation, which involves using a machine to focus beams of radiation onto the prostate from outside the body
surgery to treat symptoms of the cancer
involvement in clinical trials of newer treatments
People with prostate cancer will be able to discuss their treatment options with their doctor to decide the best course for them.
Does a doctor produce new Gleason scores throughout treatment to monitor the progression of the cancer?
A pathologist evaluates a person’s prostate cancer cells by comparing them with normal prostate tissue cells under a microscope using the Gleason system. This is performed after a biopsy. Unless the person has biopsies completed during the course of their treatment, the doctor will only assign a Gleason score at the time of the biopsy.
If the person has multiple biopsies during the course of treatment, a pathologist will run a report on those cells using the Gleason system. Measuring the progress of the cancer treatment, however, is completed through standard of care imaging to measure the size of tumors.
Sometimes, a doctor can use blood biomarkers such as PSA to measure the progress of treatment. The doctor will tell the person what methods they will use to track the progress of the treatment’s success.Christina Chun, MPH Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.