Utility of saturation biopsy to predict insignificant cancer at radical prostatectomy

Objectives. To determine whether potential candidates for watchful waiting have undersampling of more substantial cancer. Methods. A total of 103 men were studied, who were predicted to have insignificant cancer in their radical prostatectomy (RP) specimen. All had limited cancer on routine needle biopsy (no core with more than 50% involvement; Gleason score less than 7, and fewer than 3 cores involved) with a serum prostate-specific antigen density of 0.15 or less. Insignificant tumor at RP was considered organ-confined tumor, no Gleason pattern 4 or 5, and a tumor volume of less than 0.5 cm³. Saturation biopsy (average 44 cores) and an alternate biopsy saturation scheme with one half the number of cores using an 18-gauge Biopty gun was performed in the pathology laboratory on totally embedded and serially sectioned RP specimens. Results. Of the tumors, 97% were organ confined. The RP Gleason score was less than 7 in 84% of the cases. The RP tumor volume was 0.01 to 2.39 cm³ (median 0.14). Of the cancer specimens, 71% were insignificant and 29% had been incorrectly classified before surgery using standard biopsy schemes. Using the full saturation biopsy scheme, if we predicted significant cancer, the probability of having insignificant cancer was only 11.5% (false-positive rate). If the model predicted insignificant cancer, the probability of significant cancer was also only 11.5% (false-negative rate; sensitivity 71.9% and specificity 95.8%). Using the alternate biopsy sampling scheme, the false-positive rate was 8% and the false-negative rate was 11.4% (sensitivity 71.9% and specificity 97.1%). Conclusions. Saturation biopsy provides accurate predictability of prostate tumor volume and grade to select suitable candidates for watchful waiting therapy.