The Gleason score is the number that decides whether you are recommended surgery, radiotherapy or active surveillance. But it is a system from the 1960s that rests on a human assessment of complex biological information, and research shows that the same biopsy can result in different answers depending on who reviews it.
The history behind the Gleason score
The system is named after the pathologist Donald Gleason, who in the 1960s developed a method for grading the aggressiveness of prostate cancer by studying how the structure of the tissue deviates from the normal. The modern standard system, ISUP grading, divides prostate cancer into five groups (1–5) with increasing aggressiveness. But the foundation is still the same: a human pathologist reviewing tissue under a microscope.
How the grading works
At a biopsy session, several tissue samples are taken from the prostate. Each sample is sent to a pathology laboratory, where a specialist reviews the samples. The pathologist looks at how the cancer cells appear and organise themselves, and assigns a Gleason pattern (1–5) for the most common and the second most common pattern. The two values are added together into a Gleason score, for example 3+4=7. The combined value, converted into an ISUP grade group, is what your doctor then bases their recommendation on.
The problem with the system
The system is well tried and widely accepted, but it has one fundamental problem: it rests entirely on a human assessment of complex biological information. A Dutch nationwide study of 35,258 patients showed that inter-observer variability (the difference in assessment between different pathologists) is considerable. International studies indicate that up to 20 per cent of assessments differ when they are reviewed by another specialist. We go through the limitations of the Gleason method in more detail on a separate page.
The consequences in practice
A man with prostate cancer who is assessed as ISUP 2 by one pathologist may be assessed as ISUP 1 by another, and end up in active surveillance instead of surgery, or the other way around. Every step on the ISUP scale can have a direct effect on which treatment option is recommended. A patient whose aggressiveness is underestimated may miss out on treatment. A patient who is overestimated risks surgery with a risk of lasting side effects for a cancer that could have been monitored.
Is there a better alternative?
Gleason grading and the ISUP system are the standard today and are not being replaced. But they can be complemented. PCAI is an AI-based system trained on actual patient outcomes and validated in a study of 25,591 patients, not on a single pathologist's assessment. It gives a prognostic index based on what research actually knows about how cancers with a similar appearance develop in real patients. It is a complement, an independent voice in an important dialogue. Read more about PCAI.
You may also find answers here:
- PCAI vs. Gleason score – a direct comparison PCAI vs. Gleason
- How certain is your prostate cancer diagnosis, really? Article 2 – How certain is the diagnosis
- Can AI really analyse cancer better than a specialist?
What does your Gleason number mean for you?
An independent analysis of the same tissue sample can give a more reassuring basis for the treatment decision.