A Gleason score is the result of a system that rates how closely a prostate tumor resembles normal prostate tissue. A grade is assigned to the two largest areas of cancer within the tissue and then added together to produce the score. A tumor with a low score is likely to be slow-growing; one with a high score is likely to grow more aggressively.
What Is a Gleason Score?
A prostate cancer diagnosis is made by looking at prostate tissue under a microscope. A pathologist (a doctor who identifies diseases by studying tissues under a microscope) will look at the biopsied tissue for prostate cancer cells. Once prostate cancer has been identified, the doctor must determine both the stage and grade of the cancer.
Using a Gleason Score to Grade Prostate Cancer
Grade describes how closely the tumor resembles normal prostate tissue. One way of grading prostate cancer is called the Gleason system. This system uses a Gleason score of 2 to 10 to grade prostate cancer. 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.
The Gleason score offers a good clue to your tumor's behavior: A tumor with a low Gleason score is likely to be slow-growing, while one with a high score is more likely to grow aggressively or to have already spread outside the prostate (metastasized).
The Gleason grading system assigns a grade to each of the two largest areas of cancer in the tissue samples. Grades range from 1 to 5, with 1 being the least aggressive and 5 the most aggressive. Grade 3 tumors, for example, seldom have metastases, but metastases are common with grade 4 or grade 5.
The two grades are then added together to produce a Gleason score. A score of 2 to 4 is considered low grade; 5 through 7, intermediate grade; and 8 through 10, high grade.
A tumor with a low Gleason score typically grows slowly enough that it may not pose a significant threat to the patient in his lifetime.
(Click Prostate Cancer Diagnosis to read more about how the Gleason score and prostate cancer grade and stage are used when making a prostate cancer diagnosis.)