Biopsy remains the gold standard for confirming a diagnosis of prostate cancer following an elevated PSA or an abnormal digital rectal exam. It consists of taking several small fragments of prostate tissue, under local anesthesia, often guided by ultrasound or MRI, in order to analyze them under a microscope.
1. The Gleason score: assess cell architecture
The Gleason score, created in the 1960s by pathologist Donald Gleason, assesses the degree of differentiation of cancer cells seen under a microscope — that is, how closely they still resemble normal prostate cells. A grade of 3 corresponds to cells that are well differentiated and close to normal; a grade of 5 corresponds to very disorganized and aggressive cells.
The final score is calculated by adding two grades: the grade most represented in the samples, and the highest grade observed. For example, a score “7 (3+4)” means that grade 3 is the majority, with a grade 4 component — a different profile, and with a better prognosis, than a score “7 (4+3)” where grade 4 is the majority, although the total is identical.
2. The ISUP classification: a simplified reading in 5 groups
To make reading the Gleason score more intuitive, the International Society of Urological Pathology (ISUP) proposed in 2014 a system of prognostic groups, graded from 1 (the most favorable) to 5 (the most aggressive).
| Group ISUP | Corresponding Gleason Score | Risk Level |
|---|---|---|
| ISUP 1 | 6 (3+3) | Low risk |
| ISUP 2 | 7 (3+4) | Favorable intermediate risk |
| ISUP 3 | 7 (4+3) | Adverse intermediate risk |
| ISUP 4 | 8 (4+4, 3+5 or 5+3) | High risk |
| ISUP 5 | 9 or 10 | Very high risk, aggressive shape |
This table helps to navigate, but never replaces the complete analysis of the file: two men with the same ISUP group may have different management strategies depending on their PSA, their MRI, their age and the volume of cancer found.
3. What the report contains beyond the score
The Gleason score and ISUP group are only part of the information provided by the biopsy. The report also specifies the number of positive samples out of the total number taken (an indicator of the estimated tumor volume), the length of cancer found in each sample, and the location (right side, left, or both) — all elements which refine the overall assessment of risk, beyond just the score.
4. A part of variability to know
A less known but important element: the Gleason score established on the biopsy may differ from that obtained after a possible prostatectomy (complete removal of the prostate), because the biopsy only examines a limited sample of the tissue. Studies report significant discordance rates, most often due to underestimation of the grade on the initial biopsy. This variability explains why the Gleason score is always interpreted with caution, in addition to other examinations (PSA, MRI), and why a re-evaluation is sometimes necessary during follow-up.
⚠️ To remember from a medical point of view
The Gleason score and the ISUP group guide the management but do not determine it alone: age, general health, PSA and the patient's wishes all come into play.
A Gleason score 6 (ISUP group 1) corresponds to a form of low risk, for which active surveillance — without immediate treatment — is today a standard option, which we will detail in the next article.
A discrepancy between the biopsy score and that of a subsequent analysis (after surgery) is not a medical error: it reflects the limitations inherent in biopsy sampling.
Tips to remember:
- ●The Gleason score adds the most frequent grade and the highest grade observed under the microscope: a “7 (3+4)” has a better prognosis than a “7 (4+3)”, although the total is identical.
- ●The ISUP classification (1 to 5) simplifies the reading of the Gleason score into five prognostic groups, from the most favorable to the most aggressive.
- ●The biopsy report contains much more than just the score: number of positive samples, tumor length and location refine the risk assessment.
- ●The Gleason score obtained by biopsy may differ from that observed after possible surgery, because the biopsy only examines a limited sample of prostate tissue.
- ●A Gleason score 6 (ISUP 1) corresponds to a form of low risk, for which active surveillance is today a recognized option — subject of the next article in this series.
