Evidence of Benefit
The Gleason score is an important prognostic measure relying on the pathologic assessment of the architectural growth patterns of prostate biopsy. The Gleason grading system assigns a grade to each of the two largest areas of prostate cancer in the tissue samples. A sampling of eight or more biopsy cores improves the pathological grading accuracy. Grades range from 1 to 5, with 1 being the most differentiated and 5 the least differentiated. Grade 3 tumors seldom have associated metastases, but metastases are common with grade 4 or grade 5 tumors. The two grades are added together to produce a Gleason score. A score of 2 to 4 is rarely given, 5 to 6 is low grade, 7 is intermediate grade, and 8 to 10 is high grade. The overall rate of concordance between original interpretations and review of the needle biopsy specimens has been reported to be 60%, with accuracy improving with increased tumor grade and percentage of tumor involvement in the biopsy specimen.
As of 2005, approximately 90% of prostate cancers detected are clinically localized and have more favorable tumor characteristics or grades than the pre-PSA screening era. A retrospective population-cohort study using the Connecticut Tumor registry reviewed the mortality probability from prostate cancer given the patient's age at diagnosis and tumor grade. Patients were treated with either observation or immediate or delayed androgen withdrawal therapy, with a median observation of 24 years. This study was initiated before the PSA screening era. Transurethral resection or open surgery for benign prostatic hyperplasia identified 71% of the tumors incidentally. The prostate cancer mortality rate was 33 per 1,000 person-years during the first 15 years of follow-up (95% CI, 28-38) and 18 per 1,000 person-years after 15 years of follow-up (95% CI, 10-29). Men with low-grade prostate cancers had a minimal risk of dying from prostate cancer during 20 years of follow-up (Gleason score of 2 to 4; six deaths per 1,000 person-years; 95% CI, 2-11). Men with high-grade prostate cancers had an increased probability of dying from prostate cancer within 10 years of diagnosis (Gleason score of 8 to 10, 121 deaths per 1,000 person-years; 95% CI, 90-156). Men with tumors that had a Gleason score of 5 or 6 had an intermediate risk of prostate cancer death. The annual mortality rate from prostate cancer appears to remain stable after 15 years from diagnosis.
A computer simulation model has been developed to analyze the trends in prostate cancer detection (PSA screening beginning in approximately 1988) to compare these trends with the reported fall in prostate cancer deaths observed between 1992 and 1994. The level of screening efficacy was hypothesized to be similar to those postulated in the PLCO. The changes in prostate cancer mortality could not be explained entirely by PSA screening alone.