The histological grade (degree of malignancy) of prostate cancer is determined by a pathologist on the basis of a microscopic examination, using the international Gleason grading system. The system was named after the pathologist Donald Gleason. It is based on the histological grade of the glandular structures of prostate cancer tissue or the difference in appearance compared with a normal structure. The higher the Gleason score, the greater the difference and the more malignant (aggressive) the cancer. A well-differentiated, nearly normal glandular structure indicates low malignant potential, while a poorly differentiated (very much changed) structure indicates an aggressive cancer. The grade of the change caused by the cancer is evaluated on a scale from 1 to 5, so that the two most prevalent (primary and secondary) patterns are separately graded from the sample of cancer tissue. These figures are added up, giving the final Gleason score.
In theory, the Gleason score can vary from 2 to 10, with 10 being the worst score. After the introduction of current advanced techniques in pathological diagnosis, it became evident that low Gleason scores are practically not found in prostate cancer. Thus, Gleason scores for prostate cancer usually range from 6 to 10. The score ‘6’ usually indicates a good prognosis. Very high Gleason scores (8 to 10) indicate an aggressive high-risk cancer. A higher risk also indicates a higher recurrence tendency. This is taken into account in the individual implementation of treatment.
Only a few years back, it was generally thought that all GS6 cancers are highly curable with all treatments, while prostate cancers with a score of GS8 or higher (GS9, GS10) are never completely curable. Even if a GS8–GS10 prostate cancer initially seemed localised, it has turned out that these cancer cells can very early invade areas outside the prostate, making the cancer challenging to treat. On the other hand, after learning this from various studies and treatment experience, the treatment of these cancers has become more efficient, so that an increasingly high percentage of GS8–10 cancers can be completely cured. The treatment of these cancers should also include destroying the invisible cancer cells that probably exist outside the prostate. In practice, the best method for this is radiation therapy and pharmacotherapy combined with other treatments, which is also the case with the treatment of other cancers today.
Approximately 70% of patients with a Gleason score of 6 (or lower) have a localised prostate cancer. In our experience, the fact that Gleason 6 cancer does not usually even show in MRI scans is also a sign of an early stage and good prognosis. If the Gleason score is 8 or higher, the prostate cancer has often already spread at the time of diagnosis. In localised prostate cancer, however, the Gleason score is just one factor contributing to the prognosis. Other factors include the PSA level and its increase rate and local spreading (can be determined with a multiparametric MRI scan and PET-CT scans using various radiopharmaceuticals), as well as the possible spreading outside the prostate.