Nuclear grading versus Gleason grading in small samples containing prostate cancer: a tissue microarray study

In this study we addressed the question whether nuclear grading in very small samples of prostate cancer would provide additional prognostic information as compared to Gleason grading. Therefore, a tissue microarray (TMA) was constructed comprising a total number of 3,261 prostate cancers. Blinded for all clinical and pathological data, the TMA spots (diameter 0.6 mm) containing cancer were graded with two systems: First, for nuclear features according to a modified Fuhrman grading system, and second, by using a simplified Gleason system. The results were compared with tumour stage, tumour grade and follow-up data. Although nuclear grading could easily be performed on the TMA spots, no correlation was found with tumour stage, grade or PSA recurrence after prostatectomy. However, Gleason grading, even when performed on the small TMA spots, provided significant prognostic information. Correlation with Gleason scores determined in the complete prostatectomy specimens showed moderate agreement in low-grade (score ≤ 6) or intermediate (score = 7) tumours, but poor agreement with high-grade (score ≥ 8) tumours. In conclusion, the Fuhrman grading of prostate cancer does not appear to be of any prognostic importance so the Gleason grading remains the system of choice, even in tumour specimens smaller than 1 mm.