Grading indicates how cancer cells appear and behave compared to normal cells. Pathologists in the lab determine the grade of each case based on the Gleason classification system. This system gives an idea of how quickly the cancer may grow and spread. The Gleason scale helps to predict your prognosis and how the cancer might respond to treatment.
Gleason Classification System
The Gleason classification system is used to classify adenocarcinoma, the most common type of prostate cancer. There are five patterns of prostate cancer cells based on their differentiation. The lower the pattern number, the more cells appear and behave like normal cells. Gleason patterns 1 and 2 are not commonly used because these cells look a lot like normal cells. The grade of the cancer corresponds to the pattern number. Most prostate cancers have a Gleason pattern of 3, 4 or 5.1
Calculating the Gleason Score
To make the Gleason score easier to understand, doctors have developed the Grade Group (GG) system. This gives a single score from 1 to 5 based on increasing Gleason scores. For example, GG 1 corresponds to a Gleason score 6 and GG 5 corresponds to Gleason score 9 or 10.
Typical Gleason Scores range from 6-10. The higher the Gleason Score, the more likely that the cancer will be aggressive.2
- Scores of 6 or less describe cancer cells that look similar to normal cells and suggest that the cancer has a slow growth rate.
- A score of 7 suggests an intermediate risk for aggressive cancer. Having a score of 7 means that the primary score (largest section of the tumour) scored a 3 or 4. Tumours with a primary score of 3 and a secondary score of 4 have a fairly good outlook, whereas cancers with a primary Gleason Score of 4 and a secondary score of 3, are more likely to grow and spread.
- Scores of 8 or higher describe cancers that are likely to spread more rapidly, these cancers are often referred to as poorly differentiated or high grade.
Staging describes where the cancer is located in the body when it’s first diagnosed. The results from the tests performed to diagnose the cancer are used to determine the size of the tumour, which parts of the organ have cancer and whether it has spread. Staging information also helps healthcare providers determine the best course of treatment for an individual as well as their prognosis.
The TNM system establishes 4 stages for prostate cancer: stages 1 to 4 are written as the Roman numerals I, II, III and IV. Generally, the higher the stage number, the more the cancer has spread.3
When describing the stage, doctors often use the words localized, locally advanced or metastatic.
- Localized indicates the cancer is only in one area and hasn’t spread to nearby tissues or to distant parts of the body. Localized prostate cancer includes stage 1 and stage 2.
- Locally advanced prostate cancer suggests the cancer has grown through the covering of the prostate (the capsule) to nearby tissue. Locally advanced cancer includes stage 3 and 4.
- Metastatic prostate cancer means the cancer has spread beyond the tissues surrounding the prostate to other parts of the body.
Doctors may also use the words local, regional or distant when describing the cancer.
- Local means the cancer has not spread to other parts of the body.
- Regional means the cancer has spread to neighbouring tissues or organs.
- Distant means the cancer has spread to other parts of the body.
TNM Staging System
The TNM staging system is used to describe the amount and spread of cancer in a patient’s body, using the TNM descriptors.4
T describes how much of the prostate contains cancer and if doctors can feel the cancer or see it on imaging tests. It also describes if the tumour has grown outside of the prostate to the surrounding tissues. T is usually given as a number from 1 to 4. The higher the number, the larger the tumour is in the prostate.
N describes whether or not cancer has spread to lymph nodes near the prostate. N0 means the cancer hasn’t spread to any nearby lymph nodes. N1 means cancer has spread to nearby lymph nodes.
M describes whether or not the cancer has spread or metastasized to other parts of the body. M0 means that cancer has not spread to other parts of the body. M1 means that it has spread to other parts of the body.
Recurrent Prostate Cancer
Recurrent prostate cancer means that the cancer has come back after it has already been treated. If it comes back in the same place that the cancer first started, it’s considered a local recurrence. If it comes back in tissues or lymph nodes close to where it first started, it’s called regional recurrence and when it recurs in other parts of the body it’s called distant metastasis or distant recurrence.
A biochemical recurrence of prostate cancer is when the levels of prostate-specific antigen (PSA) increase quickly after the initial treatment but there are no other signs of cancer.
Cancer cells can spread from the prostate to other parts of the body. This spread is known as metastasis. The most common sites for prostate cancer metastasis are the:
- Ejaculatory ducts (the ducts that run from the seminal vesicles to the part of the urethra that passes through the prostate)
- Lymph nodes in the pelvis
- Lymph nodes outside the pelvis
- Pelvic wall
- Seminal vesicles (the glands on each side of the prostate)
- Urethra (the duct that conducts urine and semen through the penis)