Understanding the Gleason Score

Since the 1960s, the Gleason score has been used to classify prostate cancer based on how abnormal the patterns and arrangements of cells are at the microscopic level. As the cancer progresses, prostate gland cells tend to spread out, and lose their original shape.

To determine your Gleason score, ten to twelve samples of the tumor tissue core may be extracted during a prostate biopsy to observe these microscopic patterns. The goal here is to facilitate the grading and staging of your prostate cancer, helping clinicians to predict your prognosis and pick the best treatment for you based on past data.

Overall, Gleason patterns 1 and 2 are rarely seen in prostate cancer, but generally appear as normal healthy prostate cells, which are small, look similar and are arranged closely packed together. In pattern 2, cells are larger, with greater space in between them.

The most commonly seen Gleason pattern 3, is made up of cells that still sit separately from each other. They may vary in size, and include cells that branch outwards.

Gleason pattern 4 however, includes irregularly-shaped cells that tend to fuse together. Some may feature the “cribriform” pattern, which features small holes and is associated with worsened outcomes post-treatment. Gleason pattern 5 no longer has individual glands, and is instead made up of cords and sheets of tumor cells.

However, most tumors generally feature a few different patterns. To deal with this, the scoring system was designed to pick the most common and highest pattern scores and add them together as a mathematical equation (e.g. 4+3 = 7). This helps to differentiate between tumors with greater accuracy. Currently, Gleason scores usually range from 6 to 10. As scores go up, they are associated with increased risk of failed treatments, advanced spread and death.

Over the past decade, an improved and simplified grading system has been designed to match these Gleason scores to new prostate cancer grades, ranging from 1 to 5, to better categorize your risk level:

Generally, a high grade prostate cancer suggests a poorer prognosis. You may also wonder why Grade 3 (with a Gleason score of 4+3) is ranked worse than Grade 2 (with a Gleason score of 3+4) despite having the same overall score of 7. Here, the first number taken to calculate the Gleason score is based on the pattern taking up the largest tumor area. The second number selected is then based on the next largest area. Therefore, in Grade 3 prostate cancer, the tumor’s most dominant pattern is worse than that seen in Grade 2 prostate cancer.

In a large study of over 20,000 men across the US and Sweden, this grading system was used to estimate how likely cancer patients who underwent radical prostatectomy are to stay cancer-free after five years:

Going further, the chances of death or further spread for Grade 1 prostate cancer cases who continued with active surveillance was estimated to be below 1%, even after 10 or 15 years.

While useful in identifying your cancer prognosis, the Gleason score only considers your cancer status at the microscopic level. This data should still be combined with the results of your tumor staging, as well as prostate-specific antigen levels in order for your doctor to better determine your risk and the treatments best suited for you.