Diagnostic accuracy of extended biopsies for the staging of microfocal prostate cancers in autopsy specimen

Clinically insignificant prostate cancers may be predicted when biopsies show a microfocal cancer (MiFC). However, at least one-third of MiFC are underestimated by biopsies. The aim of this study was to evaluate the staging accuracy of different biopsy regimen showing a MiFC. We performed 18 biopsy cores on 164 autopsy prostates. Six cores were taken from the mid-peripheral zone (MPZ), 6 from the lateral PZ (LPZ) and 6 from the central zone (CZ). We tested seven different biopsy regimens by distinguishing the MPZ, LPZ or CZ biopsies either separately or associated with each other. Of the cancers detected by biopsies, we selected those showing a MiFC and compared our findings with whole mount analysis. The positive predictive value of a MiFC referred to how often, when needle biopsies showed a MiFC, there was a clinically insignificant cancer on whole mount prostate analysis. We found that the positive predictive value of a MiFC on 6 or 12 biopsy cores was similar irrespective of biopsy location (P ≈ 1). On MPZ, MPZ plus LPZ and all 18 biopsies, it was 40, 70 and 87%, respectively (P < 0.1). Tumor volume of cancers showing a MiFC on MPZ biopsies was significantly higher than those showing a MiFC on MPZ plus LPZ, or all 18 biopsies (P < 0.05). These results show that performing additional cores in case of MiFC on sextant biopsies may help differentiating significant from insignificant cancers.