Recutting Blocks of Prostate Needle Biopsies: How Much Diagnostic Yield Is Gained?

Objectives. The criteria for "active surveillance" depend in part on quantification of tumor extent and grade on prostate biopsies. It is known that false-negative biopsies may occur from incomplete sectioning of cores within the paraffin blocks. Methods. We retrospectively analyzed a prostate biopsy series, which were subjected to a second round of sections, in order to determine the rate of missed cancers. Results. Of 1324 sets of prostate biopsies, 4.5% (60) showed additional involved cores or higher grade tumor on recut sections. In 27 patients (2.0%), the changed diagnosis resulted in a potential mild increase in National Comprehensive Cancer Network (NCCN) risk, from negative to very low (12), very low to low (12), and low to favorable intermediate (3). In 3 patients (0.2%), the changed diagnosis resulted in a significant increase in NCCN risk. Comparison of the initial sets of slides to the recuts demonstrated areas of absent tissue in many of the cases in which tumor segments were missed. In 2/3 cases with the significant grade increase, gaps were present in one that should have alerted the pathologist to incomplete sections, and the tumor was fragmented at the edge of the core appearing incompletely sampled. Conclusions. A significant increase in risk was seen in this study in 0.2% of patients when blocks were recut for further sampling, with minor increases in 2%. While embedding issues only rarely resulted in clinically significant sampling error, the 3 significantly underdiagnosed cases underscore the need for pathologists to be alert to incomplete sections of prostate cores.