Staging and Grading
Grading refers to how abnormal the cells look under a microscope and how likely the cancer is to advance and spread. A pathologist will read the biopsy report and assign a grade to the tumor cells using the Gleason system of scoring.
Staging refers to the extent the cancer has spread. Based on the grade, TNM staging system, PSA test result, digital rectal exam, and possibly imaging tests, the doctor stages the cancer. The overall stage cancer can help the doctor determine treatment options.
The Gleason Grading System
Gleason Grade. The Gleason system grades tumors on a scale of 1 - 5 based on how well or poorly differentiated the cancer cells look under a microscope. Grade 1 means that the cells resemble normal prostate tissue. Grade 5 means that the cells look very abnormal and are poorly organized throughout the prostate. Grades 2 - 4 fall in between with cells showing increasingly irregular features.
Gleason Score. Most prostate cancers contain a mix of tumor grades. To determine a Gleason score, two numbers are assigned, representing the dominant grade and then the minor grade. The cancer is then "scored" by adding the dominant grade plus the minor grade. For example, a tumor with a dominant grade of 3 and a minor grade of 4 is given a Gleason score of 7.
Gleason scores range from 2 - 10. A higher score means that the cancer cells look very different from normal cells. A higher score also means that it is more likely that the tumor will spread aggressively. In general, Gleason scores indicate:
- Scores 2 - 4: G1. Low-grade cancer (well-differentiated cells)
- Scores 5 - 7: G2. Intermediate-grade cancer (moderately-differentiated cells) Most prostate cancers fall into this category, making it difficult to predict their development.
- Scores 8 - 10: G3 - 4. High-grade cancer (poorly-differentiated cells)
TNM Staging System
A tumor's stage is an indication of how far it has spread from its original site. Cancers are staged according to whether they are still localized (still within the prostate gland) or have spread beyond the original site. The current prostate cancer staging system is the TNM system.
The TNM system refers to clinical tumor stages as:
- T for tumor
- N for regional lymph nodes
- M for metastasis (tumors developing outside the prostate)
Review Date: 07/26/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.