Optimal method for measuring tumor extent in needle biopsy specimens to identify small-volume prostate cancer

Objectives: To compare various methods for measuring tumor extent in prostate biopsy specimens to identify small-volume prostate cancer. Methods: A total of 100 radical prostatectomy specimens were retrospectively analyzed. Receiver operating characteristic analysis was used to compare the abilities of prostate-specific antigen density, and four measures of tumor extent in prostate biopsy specimens - positive core number, greatest percentage of cancer in a single core, greatest length of cancer in cores and total length of cancer in cores - to identify small volume prostate cancer. Four definitions of insignificant cancer volume were used in this analysis: index and total tumor volume <0.5 mL, index tumor volume <1.3 mL and total tumor volume <2.5 mL. Multivariate analysis was also used to evaluate variables for predicting small-volume prostate cancer. Results: Total length of cancer in cores had the highest areas under the curve of all the measures defining small-volume prostate cancer: index tumor volume <0.5 mL (0.855), total tumor volume <0.5 mL (0.877), index tumor volume <1.3 mL (0.784) and total tumor volume <2.5 mL (0.818). On multivariate analysis total length of cancer in cores was an independent predictive factor for prostate cancers with index tumor volume <0.5 mL (P < 0.001), <1.3 mL (P < 0.001) and total tumor volume <0.5 mL (P < 0.001), respectively. Conclusion: Our data suggest that total length of cancer in cores is the optimal measure of tumor extent in prostate biopsy specimens for identifying small-volume prostate cancer.