Comparison of two commonly used methods in measurement of cancer volume in prostate biopsy

Currently, cancer volume in prostate biopsy samples is commonly calculated as linear length of carcinoma divided by total core length and reported as percentage involvement. The measurement of the linear length of carcinoma can be problematic particularly when there are two or more separate foci of carcinoma in a single core. There are two most methods commonly used by practicing pathologists. One method is to measure the exact linear extent of each discrete carcinoma foci in millimeters and then add up the linear length (the exact method, E method). The other method is to measure the core length encompassing all carcinoma foci including the intervening benign prostate tissue (glands and/or stroma) (the scattered method, S method). In this study, we used digital pathology to compare the site-specific and overall cancer volumes measured with the E and S methods and analyzed their correlation with the cancer volume in the corresponding prostatectomy specimens. Our results showed that prostate-cancer volumes estimated with both E and S methods on biopsy samples positively correlate with cancer volume at radical prostatectomy. However, the cancer volumes measured with both E and S methods in the majority of biopsy samples were significantly larger than that in prostatectomy (P<0.001). The E method more closely predicts the cancer volume compared to the S method. The overall cancer volume is better than site-specific cancer volume at biopsy in predicting cancer volume at prostatectomy.