The appearance and arrangement of cancer cells allow physicians to determine the grade of your cancer.
The American Cancer Society - Prostate Cancer Stages and Grades
Tissue taken from the prostate during biopsy is examined by a pathologist under a microscope. The pathologist looks at both the arrangement and appearance of the cancerous cells to assign a Gleason grade and a composite Gleason score.
The Gleason grading system is a grade given to prostate cancer on a scale of 1-5. The lower end of the scale indicates a low grade cancer, with 1 being extremely close to healthy prostate tissue. Grade 3 is the cellular pattern most often observed in prostate cancer and features cells and prostate glands that are large, shaped irregularly, and spaced irregularly. Gleason grade 5 tissue is very irregular with sheets or nests of irregular cells.
An individual with prostate cancer may display more than one class of Gleason grade in the tissue that was obtained from their biopsy. The grade that comprises most of the tumour volume is called the “primary pattern” and the grade that comprises less of the tumour is called the “secondary pattern”. The grades of the primary and secondary pattern are added together to create a composite called the Gleason Score, which can range from 2 to 10 (1 to 5 + 1 to 5). For example, if a man is found to have a tumour that is mostly Gleason grade 3 with a smaller amount of Gleason grade 4, his Gleason score will be 7.
The composite number should be approached with caution, because there are many different ways to arrive at a Gleason score which could mean that one individual’s Gleason 7 cancer is more aggressive than another’s. For example, Gleason 7 could be due to 3+4 or 4+3, the latter behaving more aggressively because the primary number is higher.
Gleason score is divided to three groups according to the risk of progression and metastasis.
A low grade Gleason score is considered 2-6, where the cells tend to grow slowly and is therefore considered low risk. In some cases, your doctor will suggest a period of monitoring before treatment, or a minimally invasive focal therapy.
A moderate grade Gleason score is considered 7.
A high grade Gleason score is considered 8-10, where the cells tend to grow rapidly and pose a high risk to advance.
The Gleason score is an important part of a prostate cancer diagnosis, but there are many other factors which can influence the decision of which treatment will be best for each individual.