Gleason Score: definition and explanation

Recognized as a major prognostic factor for prostate cancer, the Gleason score is today a prostate cancer key indicator that needs to be defined and explained. Calculating the Gleason score allows doctors to measure the extent and aggressiveness of the disease. The prostate cancer treatment to be offered is partly dependent on the Gleason score.

Gleason Score: definition

The Gleason score shows how aggressive prostate cancer is. This is the most commonly used scale. Gleason score determination is based on the biopsies’ analysis. The prostate gland contains several disease locations with different evolutions and with different stages of differentiation.

The Gleason score is obtained by adding the 2 histological grades from 1 to 5 of the most represented cancers. It should be noted that biopsy only reflects a part of the gland. It’s a tissue sample. However, the Gleason score remains the most powerful prognostic factor for prostate cancer today.

The different kinds of Gleason score

The ranks of Gleason score

Gleason score calculation will make it possible to classify cancer cells according to different kinds. A scale from 1 to 5 will rate the aggressiveness of prostate cancer.

  • Grade 1: the cells appear normal
  • Grade 2: the cancer appears to be weak
  • Grade 3: mid-stage disease
  • Grades 4 and 5: the cells have an irregular and abnormal appearance; prostate cancer is considered aggressive.

It should be noted that several grades can coexist within the same tissue sampled during the biopsy.

Gleason Score calculation

After biopsies analysis, the Gleason score is presented as follows:

  • Gleason 7 (3+4) noted 3-4
  • Gleason 10 (5+5) noted 5-5

The first number in brackets corresponds to the kind of cancer cells most present in the sampled tissue. The second number in brackets indicates the 2nd most common cell kind always present in the same tissue sample. These two figures correspond to the grades mentioned above. The Gleason score (7 and 10 in the above examples) is obtained by addition of these 2 figures together. It is between 6 and 10 depending on how aggressive the cancer is.

  • A Gleason score of 6 is in general considered as a low-risk prostate cancer (depending on other factors such as MRI, PSA and stage)
  • A Gleason score of 7 indicates in general an intermediate-risk cancer.
  • A Gleason score of 8 to 10 implies high-risk prostate cancer.

To be noted: The Gleason score cannot be evaluated after some prostate cancer treatments that have already been performed. This applies with hormone therapy, external radiotherapy and brachytherapy.