PROSTATE CANCER GRADING

Prostate cancer grading
Adenocarcinoma of the prostate is graded using the Gleason system. Microscopically, adenocarcinoma is graded 1 to 5 according to its gland-forming differentiation at relatively low magnification. Cytological features play no part in this grading system. Since most are multifocal, an allowance is made by adding the two dominant grades to give a sum score between 2 and 10. If only one pattern is observed, the grade is simply doubled. The system is used with needle biopsies, TURP, and radical prostatectomy specimens.

Gleason scores 2 - 4 are considered well differentiated; 5 - 7 are moderately differentiated; and 8 - 10 are poorly differentiated. In practice, 75% of PCs are graded 5, 6, or 7; 10% are graded 2 - 4; and, fortunately, only 15% are graded 8 - 10. Among expert pathologists there is good inter-observer reproducibility with Gleason scoring. However, scores assigned to needle biopsies are lower than those assigned to the subsequent radical prostatectomy specimen in 30 - 40% of cases, while overgrading on needle biopsy is uncommon.

The importance of the Gleason score is that it correlates well with prognosis, stage for stage, however the patient is managed. For example, a Gleason 3+3 = 6 adenocarcinoma carries a worse prognosis than a 3+2 = 5 cancer of equivalent stage. Moreover, cancers of the same Gleason score have a worse prognosis if the predominant grade is higher (for example, 4+3 = 7 is worse than 3+4 = 7). Some men with low-grade tumours develop high-grade tumours after several years. This is probably due to clonal expansion of high-grade cells rather than de-differentiation of low-grade tumour cells. In general, large-volume tumours are more likely to be high-grade than low-volume tumours, but occasionally exceptions are seen.

Finally, caution must be taken when Gleason-scoring prostate tissue that has been subjected to certain interventions, most notably hormone therapy. It is well recognized that prostate cancer treated with androgen ablation exhibits changes very similar to those seen in Gleason scores 8 - 10. It is possible that even treatment of BPH with 5-α-reductase inhibitors could adversely affect the Gleason score of cancer present in the gland. Pathologists are therefore keen to know relevant clinical details and are reluctant to provide Gleason scores for such patients.