The volume of prostate cancer in the biopsy specimen cannot reliably predict the quantity of cancer in the radical prostatectomy specimen on an individual basis.

Previous studies suggest that prostate cancer with a volume of 0.5 ml. or less and a Gleason score of less than 7 may be clinically insignificant and may be managed with watchful waiting. A proposed method of determining the volume of cancer in the prostate gland has been the grade and volume of cancer present in the transrectal needle biopsy specimen. Volume of cancer in the biopsy specimen as a predictor of volume of cancer in the prostate gland was studied in 130 men who underwent radical retropubic prostatectomy for adenocarcinoma. Of the men 46 (35%) had clinical stage T1c (nonpalpable) disease, while 84 (65%) had clinical stage T2 (palpable) disease. Each radical prostatectomy specimen was whole-mounted and step-sectioned for accurate cancer volume determination. Three parameters for measuring volume of cancer in the biopsy specimen (percentage of biopsy cores involved, millimeters of cancer per biopsy core and percentage of cancer in the biopsy specimen) were determined and compared by Spearman rank correlation analysis. The percentage of cancer in the biopsy specimen was marginally better than the percentage of cores involved and the millimeters of cancer per biopsy core as a predictor of cancer volume in the radical prostatectomy specimen. While regression analysis revealed a direct correlation between the volume of cancer in the biopsy and radical prostatectomy specimens (r = 0.51), there was significant variability in prostate cancer volume for a given percentage of cancer in the biopsy specimen since the standard error of the estimate was 6.1 ml. Of the 13 patients with 5% or less cancer volume and a Gleason score of less than 7 in the biopsy specimen 1 (8%) had a cancer smaller than 0.5 ml. in volume in the radical prostatectomy specimen. Therefore, the risk of removing clinically insignificant prostate cancer, even when the biopsy parameter indicates low volume disease, is less than 10%. Overall, only 3 study patients (2.3%) had a prostate cancer volume of less than 0.5 ml. With 97.7% of the men having a clinically significant cancer by a volume criterion, it is apparent that the majority of clinically insignificant prostate cancers remained undetected and untreated. Currently, transrectal needle biopsy does not provide adequate information for differentiating between clinically insignificant and life threatening prostate cancer on an individual basis.