Understanding Gleason Scores and Grade Groups

The Gleason score describes how prostate cancer cells are arranged when a pathologist examines your tissue under a microscope. It is a grade, not a stage. It says nothing about the size of the tumour or whether it has spread. Areas of cancer are given a pattern number from 1 to 5, where pattern 1 looks close to normal prostate glands and pattern 5 has lost recognisable gland structure altogether.

Prostate cancer is usually patchy, with different-looking areas within the same gland. The pathologist grades the two areas that make up most of the cancer and adds them together. That is why your result appears as a sum.

The order matters. In 3+4=7, pattern 3 makes up most of the cancer with some pattern 4 present. In 4+3=7, the more abnormal pattern predominates. Both add to 7, but they are not treated as equivalent.

This is where most of the distress comes from. On paper the scale runs from 2 to 10, so a 6 looks like it sits somewhere in the middle. It does not.

Patterns 1 and 2 are essentially never assigned on modern biopsies. They were retired from routine use because pathologists could not apply them reproducibly, and because tissue once called pattern 1 or 2 often turned out not to be cancer at all. That leaves pattern 3 as the lowest in use, and 3+3=6 as the lowest score in use.

A Gleason 6 is the bottom of the range, not the middle of it. The American Cancer Society names this misunderstanding explicitly: a patient with a Gleason score 6 cancer might assume his cancer is in the middle of the range, even though grade 6 cancers are actually the lowest grade seen in practice.

Because that confusion was so widespread, the International Society of Urological Pathology introduced Grade Groups in 2014. Most reports now list both systems side by side.

• Grade Group 1 — Gleason 6 or lower
• Grade Group 2 — Gleason 3+4=7
• Grade Group 3 — Gleason 4+3=7
• Grade Group 4 — Gleason 8
• Grade Group 5 — Gleason 9 or 10

The same cancer that reads as "6" in the old system reads as "1 out of 5" in the new one, which gives a far more accurate impression of where it sits.

Grade Group 1 disease is low grade. It tends to grow slowly and very rarely spreads, and many men with it are appropriate candidates for active surveillance rather than immediate treatment. Grade Groups 2 and 3 are intermediate, and the split between 3+4 and 4+3 exists because more pattern 4 carries more risk. Grade Groups 4 and 5 are high grade and usually prompt more intensive treatment. The presence of any pattern 5, even in a small amount, raises concern about recurrence.

Grade is only one input. Your overall risk category also draws on your PSA level, your clinical stage, MRI findings, how many biopsy cores contained cancer and how much of each, and sometimes a genomic test on the tissue.

A biopsy samples narrow cores from a small part of the prostate. If the whole gland is later removed and examined, the pathologist sees the full picture and the grade may go up, or occasionally down. Grade may also be revised at a repeat biopsy during active surveillance. This reflects how much tissue was available to look at, not an error by the original pathologist.

Gleason grading is expert judgement, and the boundary between pattern 3 and pattern 4 is where experienced pathologists most often differ. That boundary is also where Grade Group 1 becomes Grade Group 2 — the line that can decide between surveillance and treatment. Asking for your slides to be reviewed by a genitourinary pathologist is a common, reasonable request, and your team can arrange it.

• Prostate Cancer Foundation: What is a Gleason Score?
• NCI: Prostate Cancer Treatment (PDQ) - Patient Version
• NCI: Tumor Grade