Your doctor will use your biopsy to determine the grade and stage of your cancer, which are important because they help to determine the best treatment options and the outlook for your recovery. The Gleason system is used to define the grade, a measure of the aggressiveness of your cancer. The TNM system is used to determine the stage, which indicates whether and how far your cancer has spread (metastasized). In addition to biopsy, other tests or procedures may be used to check for metastasis.
Grading Prostate Cancer—the Gleason System
Prostate cancer is graded using the Gleason system. Grade is based on how abnormal your cancer cells and their growth patterns look. It is an indication of how quickly the tumor is likely to grow and spread—in other words, how aggressive your cancer is. Your cancer may be low, intermediate, or high grade. Low-grade cancer is the least aggressive; high-grade cancer is the most aggressive.
Prostate cancers often have areas with different grades. To determine the overall grade of your cancer, your team will look at cells from the two areas that make up most of your cancer, and they’ll assign a Gleason grade to each area. Gleason grades range from 3 to 5. The more abnormal the cancer cells and growth patterns, the higher the Gleason grade. With a couple of exceptions, the sum of the two Gleason grades is the Gleason score. Gleason scores range from 6 to 10. The higher the Gleason score, the more likely the cancer is to be aggressive.
- A Gleason score of 6 means the cancer is low grade.
- A Gleason score of 7 means the cancer is intermediate grade.
- A Gleason score of 8 to 10 means the cancer is high grade.
Staging Prostate Cancer—the TNM System
The stage of your cancer is an indication of how far it has spread. Staging is done as part of the diagnosis process to determine how extensive your cancer is within the prostate and whether or not it has spread beyond the prostate gland to the lymph nodes or other organs.
Prostate cancer is typically staged using the TNM system, which is based on:
- The extent of the primary tumor (T category)
- Whether the cancer has spread to nearby lymph nodes (N category)
- The presence or absence of distant metastasis (M category)
- The prostate-specific antigen (PSA) level at the time of diagnosis
- The Gleason score and the amount of cancer
Using this information, prostate cancer is then grouped into stages I through IV, with stage I being the least advanced and stage IV being the most advanced.
- Stage I: Cancer is confined to the prostate. Gleason score is 6 or below. PSA level is less than 10.
- Stage II: The tumor is more advanced but does not extend beyond the prostate.
- Stage III: The tumor extends beyond the prostate and may be in a seminal vesicle. Cancer has not spread to lymph nodes.
- Stage IV: The tumor has spread to another part of the body, such as the bladder, rectum, lymph nodes, or bones.
Testing for Metastasis
In men who have high PSA levels, extensive prostate involvement on biopsy, or high Gleason scores, additional tests may be done to determine if cancer is outside of the prostate or has spread to other areas of the body. These tests may include computed tomography (CT) scans of the abdomen and pelvis, bone scans, and magnetic resonance imaging (MRI) of the pelvis. Many centers, including Seattle Cancer Care Alliance (SCCA), are testing other means of finding cancer spread using new types of positron emission tomography (PET) scans. Sometimes lymph nodes around the prostate may be checked for metastasis in order to design treatment appropriately.
At SCCA and University of Washington Medical Center, a long-term effort has identified cells in the bone marrow that originated from prostate cancer, even in the absence of other evidence of spread. With these and other studies being offered to men with advanced prostate cancer, we hope to find ways to identify men at the highest risk of relapse so this knowledge can inform our treatment recommendations.