When they are talking about prostate cancer, doctors use the term “grade” to describe the appearance of prostate cancer tissue when it is seen under a microscope. The most common system used in the USA to grade the appearance of this tissue is called the Gleason grading system, after Donald F. Gleason, MD, the physician who first described it ( shown on the right ).
The pathological grade is a way to estimate the “aggressiveness” of your cancer, or how fast it may be growing. In prostate cancer, it is very important to understand the difference between the Gleason grade of individual tumor specimens (which can be any number from 1 to 5) and the Gleason score or Gleason sum (which is always a number from 2 to 10) and which represents the actual aggressiveness of a particular patient’s cancer.
The Gleason grading system is not the only grading system in use around the world. However, because it is the one most commonly used in the USA, it is the one we will try to explain here. If your doctor talks to you about the grade of your prostate cancer, you may want to ask if it is the Gleason grading system that he or she is referring to.
At the time of initial diagnosis, the Gleason grade is one of several pieces of information determined by the pathologist who examines the biopsy specimens taken from the prostate. The Gleason grading system is based exclusively on the architectural pattern of the glands of the prostate tumor. It evaluates how effectively the cells of any particular tumor are able to structure themselves into glands resembling those seen in a normal prostate. The ability of a prostate cancer tumor to mimic normal gland architecture is called its level of differentiation, and experience has shown that a tumor whose structure is nearly normal (well differentiated) will probably have a biological behavior relatively close to normal — i.e., not very aggressively malignant.
The principle is fairly simple, and Gleason grading from very well differentiated ( grade 1 ) to very poorly differentiated ( grade 5 ) is usually done for the most part by viewing the low magnification microscopic image of the cancer. There are important additional details which require higher magnification, and an ability to accurately grade any tumor is achieved only through much training and experience in pathology.
Figure 1: Dr. Gleason’s own simplified drawing of the five Gleason grades of prostate cancer. Grade 1 appears on the far left and grade 5 on the far right.
Adapted from Gleason DF. The Veteran’s Administration Cooperative Urologic Research Group: histologic grading and clinical staging of prostatic carcinoma. In Tannenbaum M (ed.) Urologic Pathology: The Prostate. Lea and Febiger, Philadelphia, 1977; 171-198.
The Five Gleason Grades
Dr. Gleason originally developed a simple conceptual diagram (shown in Figure 1) to illustrate the continuum of deteriorating cancer cell architecture, and the four dividing lines along this continuum which he discovered are able to identify patients with significantly different prognosis derived from a study which included 2,900 patients.
If you want to understand more about the five specific Gleason grades, and see what cells of different grades look like under the microscope, you can click on the links below: