A Gleason score is a number grade assigned to a prostate cancer after it has been evaluated by a pathologist under a microscope in the lab. The Gleason score is used to calculate basic information about the cancer for the purpose of determining how severe it is and developing a treatment plan. A number of other details about the cancer are included in the pathology report so that the medical team has a complete picture of the situation.
To determine the Gleason score, a sample of tissue from the prostate is examined by a pathologist microscopically. The pathologist identifies areas of abnormal cell growth and finds the primary and secondary areas of the cancer. First, the primary area is inspected, and its appearance is compared with the Gleason scale system to determine where it falls on a scale of one to five. Then the secondary area is examined and staged from one to five as well. The Gleason score is calculated by adding the two numbers, and will range from two to 10.
The Gleason scale, named for Doctor Donald Gleason, was developed in the 1960s, and it uses cell appearance alone to grade the cancer. The scale runs from one, well differentiated cells which suggest a slow growing cancer or even a normal prostate, to five, poorly differentiated cells which indicate that the cancer is aggressive. Stages one and two on the scale are rare, because prostate cancer is usually not identified until at least part has progressed to a scale stage of three or four.
The lower the Gleason score, the better the prognosis. In some cases, a doctor may determine that the cancer is growing so slowly that treatment may not be immediately necessary, with a focus on monitoring the patient for signs of changes. A high Gleason score such as nine indicates that the cancer is aggressive and growing quickly, and that treatment needs to be decisive and equally aggressive.
The Gleason score alone cannot be used to develop a treatment plan or to make decisions about how to treat the cancer. There are a number of factors for the medical team and the patient to consider when discussing treatment options. Someone with a high Gleason score who is already dying from another condition, for example, might opt to decline treatment, assuming that it would not add much additional quality of life, and that the rigors of treatment could be very unpleasant.