There are 5 main components to staging prostate cancer.
There are 2 grading systems: Gleason Score and ISUP Grade Group. Continue reading to learn more...
Disclaimer: This information isn’t a substitute for professional medical advice, diagnosis, or treatment. You should never rely upon this article for specific medical advice. If you have any questions or concerns, please talk to your doctor.
SIZE VS. GRADE
The size and grade of your tumor don’t always predict its behavior over time. A small, high-grade cancer is much more likely to spread to other parts of the body than a large, low-grade cancer. In some cases, tumor DNA genetics and biomarkers may be better predictors of growth over time. Consult with your health care provider to find out if these options might be right for you.
PI-RADS (Prostate Imaging Reporting and Data System)
PI-RADS (Prostate Imaging Reporting and Data System) is a structured reporting scheme for evaluating the prostate for prostate cancer based on an MRI scan. The PI-RADS score is for patients who have not yet undergone therapy. The scores are:
- PI-RADS 1: very low—clinically significant cancer is highly unlikely to be present
- PI-RADS 2: low—clinically significant cancer is unlikely to be present
- PI-RADS 3: intermediate—the chance of clinically significant cancer is neutral
- PI-RADS 4: high—clinically significant cancer is likely to be present
- PI-RADS 5: very high—clinically significant cancer is highly likely to be present
In summary, PI-RADS 4 or 5 lesions have a high probability for disease that warrants targeted biopsy for confirmation. PI-RADS 1-3 are unlikely to represent clinically significant cancer.
As previously noted, prostate MRI is still a developing technology and is ideally performed and interpreted at academic centers or other prostate sub-specialty centers.
Staging Your Disease
There are 5 main components to staging prostate cancer:
- Your PSA level
- The grade of your tumor (done via biopsy)
- The stage of your tumor (termed the “T-stage” for the prostate tumor)—for example, is the prostate cancer contained completely within the prostate?
- For some men, getting imaging to determine if the cancer has spread to lymph nodes (termed the “N-stage” for nodes) or bones or other organs (termed the “M-stage” for metastasis).
- The extent of the cancer revealed by the biopsy. For example, in a typical prostate biopsy which includes at least 12 needle core samples, a cancer found in 9 of the 12 cores is a higher risk than a cancer found in just 2 of the cores.
1. PSA: A blood test.
Your doctor should have your most recent PSA tests and, if outdated, may order a fresh one. PSA can also be considered in relation to the size of the prostate, since a bigger prostate will normally make more PSA. Your PSA density (PSAD) score is calculated by taking your PSA score and dividing by the volume (size) of your prostate in grams or milliliters. PSAD values under 0.15 (e.g., a PSA of 7.5 for a 50-mL prostate) are usually considered reassuring.
2. Grade: How aggressive the cancer looks.
If prostate cancer is found when looking at biopsied tissue under a microscope, the pathologist assigns a grade to the cancer. There are 2 grading systems currently in use, which can be confusing for patients.
The original grading system for prostate cancer is called the Gleason score, which ranges from 6 to 10 (6 is low grade, 7 is intermediate grade, and a score of 8 to 10 is high grade).
In 2014, the World Health Organization replaced the Gleason score with the simpler ISUP Grade Group system ranging from 1 (low) to 5 (very high).
Many hospitals report both the Gleason score and the ISUP grade group, but there may be hospitals that still report only the old Gleason system.
ISUP Grade Group and Gleason Score Comparison
3. Tumor staging (or T-stage): The extent of the prostate cancer.
The digital rectal exam (DRE) gives information on how extensive the prostate cancer is within the prostate area. In some cases, your practitioner may order a prostate MRI to give more information if the cancer extends outside the prostate. Staging is classified as follows:
- T1: The tumor was found solely by a biopsy done due to an elevated PSA (i.e. was not detectable by DRE or imaging) or was found incidentally during an unrelated procedure. T1 tumors can be divided into T1a-T1c subcategories, depending on how the tumor was found and its size.
- T2: The health care provider felt a nodule(s) on your prostate during the rectal exam. T2 tumors can be divided into T2a-T2c subcategories, depending on the tumor location and size.
- T3: The tumor extends out of the prostate capsule. If the tumor also extends into the seminal vesicles, this is referred to as T3b, if not, it’s T3a.
- T4: The tumor invades into the rectum or bladder (advanced).
4. Evaluating for metastatic disease: Has the tumor spread beyond the region around the prostate? Aggressive cancers (e.g. PSA >20, ISUP grade group
4 or 5 [Gleason score 8-10], or stage T3-4) usually warrant imaging scans to determine the presence of metastatic disease. Some men whose cancer has less aggressive features may benefit from further imaging and they should discuss this with their doctor. This is most commonly done with a computed tomography (CT) scan or an MRI and a bone scan, although newer and more sensitive imaging technologies are in development, such as molecular PET imaging (e.g. PSMA, Axumin, Choline). It is important for your doctor to know if your cancer has spread to lymph nodes, bones or other body sites since it will influence their treatment recommendations.
5. Biopsy cores: How many were positive?
One other aspect that your physician will look at on your pathology report in addition to the grade, is the number of biopsy needle cores that contain cancer divided by the total number of cores sampled. This is referred to as percent positive cores. The higher the percentage, the more aggressive the disease generally. For example, if 12 biopsies were taken, and 4 were involved with cancer, then you would have 4/12, or 33% positive cores.
Modern pathologists do not go below Gleason 3+3 (Gleason 6, or ISUP Grade Group 1) when scoring prostate cancer tumors. If you have detectable prostate cancer, the lowest Gleason score you will receive is a 6. Many, but not all, prostate cancers in this Gleason range may be slow growing and could be appropriate candidates for active surveillance. Consult your doctor or practitioner for more information.
To learn more, please visit the Prostate Cancer Foundation at PCF.org.