If you've been diagnosed with prostate cancer, some of your first questions will likely be about how serious your condition is. Will it grow or spread? How far has it advanced?
To answer such questions, urologists use the results of prostate cancer diagnostic tests to determine two benchmarks of the cancer: grade and stage.
"Grading indicates how aggressive your cancer might be, and staging tells us how advanced your cancer is," says Dr. Brian Miles, a urologist at Houston Methodist. "You'll hear these numbers frequently as you meet with your care team, so it's important to understand what they mean and why they're important."
What is prostate cancer grading?
Prostate cancer specialists use the Gleason scoring system to estimate the cancer's grade — how quickly it might grow or spread. A Gleason score is determined using tissue samples taken from areas of your prostate during a biopsy.
"These samples are called cores and are taken from different areas within the prostate," explains Dr. Miles. "The pathologist looks closely at these 1 mm by 10-20 mm long, thin slices to analyze how aggressive the cancer might be."
Almost all cancers are diagnosed by looking at individual cellular abnormalities — but prostate cancer is an exception.
The pathologist assigns a Gleason grade for each independent area of cancer that might be present in the different cores of tissue. Grades go from 1 to 5:
- Grades 1 and 2 are not seen. Most pathologists would refer to these as suspicious but unlikely to call them cancer.
- Grade 3 through 5 are clearly definitive cancer.
"The grading system is named after a pathologist who developed it, and it has many subtleties that make it possible to see more than one grade," says Dr. Miles. "This creates a problem, though. What do we call the diagnosis when a core has multiple grades?"
For instance, a core might have a grade of 3 in one area and a grade of 4 in another. This is why the Gleason score is used — where the most common grades are noted individually but also then added together. The first number is the most common grade, and the second number is the next most common grade.
- A low-grade tumor has a Gleason score of 3+3=6 or less.
- A high-grade tumor has a Gleason score of 4+3=7 or higher.
"The way I explain this to patients is to think of the first number as there's a lot of this and the second number as there's a little bit of that," says Dr. Miles.
He notes that it's possible to have only one grade. But because prostate cancer is always talked about in terms of Gleason scores, the number is simply repeated if there is only one grade. For instance, if it is all grade 3, the Gleason score would be 3 + 3 — which Dr. Miles notes is the most common diagnosis. If it is all grade 4, the Gleason score would be 4 + 4.
"This scoring system really helps us to define whether or not a patient can avoid treatment or should strongly consider treatment," says Dr. Miles.
Other considerations — volume of cancer cells and genomic results — are sometimes incorporated. For instance, a 3+4=7 score with a low volume of Grade 4 might warrant diagnosing the cancer as low grade. Your provider will also consider genetic factors. Genomic tests show the potential for cancer to behave more aggressively based on genetic properties.
"A genomic prostate score might show a low likelihood of progression, or it may show a more advanced disease already," adds Dr. Miles.
What is prostate cancer staging?
Staging is a method cancer specialists use to indicate how advanced the cancer is — whether it's broken through the prostate's outer layer and spread to associated nearby organs, lymph glands or even the bones.
Generally, the staging of prostate cancer utilizes the TNM system:
- T stands for tumor. Can something highly suspicious for cancer be felt, does it feel localized to the prostate, or it has broken though the wall of the prostate?
- N stands for lymph nodes or lymph glands. These are part of the immune system and help prevent the spread of cancer to other areas of the body.
- M stands for metastasis. Has the cancer spread to distant parts of the body, especially the bones?
Each of these letters has associated numbers. For instance, the T scale is reflected as T1, T2, T3, etc. T1 means nothing suspicious indicating cancer is felt. The most common stage is called T1C.
"T1C means that we cannot feel anything suspicious, but a biopsy was performed due to an elevated PSA result," explains Dr. Miles. "T2 is something that can be felt but still seems localized to the prostate. T3 means something abnormal can felt and has likely broken though the wall of the prostate."
Additional tests are also performed. For instance, an MRI (magnetic resonance imaging) is always used to provide a clearer picture of whether the cancer is truly localized or spread to nearby places.
"PET (positron emission tomography) scans are now used quite commonly to let us know — at an even more microscopic level — whether the cancer has spread to other structures or areas beyond the prostate, including the pelvic lymph glands," explains Dr. Miles. "If cancer is not in the lymph glands that would be N0. If it's spread to the lymph glands, it would be N1."
If the cancer has spread to the bones, it's called M1. If not, it's M0.
"Most diagnosed men, by far, are T1C, N0 M0, which comes with a good prognosis," adds Dr. Miles.
What happens after staging and grading?
Improvements in prostate cancer screening mean that many cases are caught in the early stages before the tumor can grow and spread.
"ln addition to confirming that the cancer is localized to the prostate area, we also consider the fact that prostate cancer can often be indolent," Dr. Miles explains. "This means the cancer cells can be present for years without spreading or causing symptoms."
Extensive research shows that most men with low-grade prostate cancer do not need immediate treatment. Instead, the care team will measure the cancer markers at regular intervals to monitor for any changes.
If prostate cancer requires treatment, your specialist and care team will explain your recommended treatment plan, which can include surgery, radiation therapy and ablation therapy, among other options.
