How is prostate cancer graded?

A pathologist will grade cancer taken during a core biopsy on a numerical 10-point scale called the Gleason grading system, which indicates how severe a cancer is. Many cancers are on the lower end of the spectrum and may not need to be treated at all. There is a subset of tumors that are on the higher end of that spectrum, however, and therefore more severe. In those cases, early diagnosis may be key to saving the man’s life.

Grade describes how closely the tumor resembles normal glandular tissue of the prostate. Based on the microscopic appearance of the tumor tissue, pathologists may describe it as low-, medium-, or high-grade cancer. One way of grading prostate cancer, called the Gleason system, uses scores of 2 to 10. Another system uses G1 through G4. In both systems, the higher the score, the higher the grade of the tumor. High-grade tumors generally grow more quickly and are more likely to spread than low-grade tumors.

This answer is based on source information from the U.S National Institutes of Health.

Prostate cancer is usually categorized as low, medium and high risk. This is based on your Gleason score, your prostate-specific antigen (PSA) level and prostate exam result. Low risk means your Gleason score is six or below, your PSA is 10 or below and there is nothing that is palpable on the prostate, or if it's palpable, it's on one-half of the gland. Sometimes, on an initial biopsy, only a part of the tumor is caught on the ultrasound. Before you begin active surveillance, another evaluation with magnetic resonance imaging (MRI) and perhaps a repeat biopsy is indicated to make sure a more aggressive tumor is not being missed.