Predicting tumour location in radical prostatectomy specimens: same-patient comparisons of 21-sample versus sextant biopsy

OBJECTIVE To determine the value of a 21-sample biopsy protocol in predicting tumour localization in radical prostatectomy (RP) specimens, compared with sextant biopsies. PATIENTS AND METHODS In all, 300 consecutive patients underwent 21-sample prostate biopsies, followed by RP. The protocol consisted of sextant, three midline, six far lateral and six transitional zone biopsies. Tumour locations on biopsies and RP specimens were compared. The sensitivity, specificity, positive (PPV) and negative predictive value (NPV) and accuracy were calculated. RESULTS There was no difference between sextant and 21-sample biopsies for sensitivity (38% vs 36%; P = 0.50) and specificity (84% vs 87%; P = 0.46), but the NPV was higher for 21-sample biopsies (57% vs 68% ; P < 0.001). The PPV was higher in the sextant biopsies (74% vs 59%; P = 0.007). Sextant, transitional zone and far lateral biopsies were re-grouped in six regions. Compared with 21-sample biopsies, sensitivity (54%) and PPV (79%) were higher (P < 0.001), while specificity (74%) and NPV (46%) were lower (P = 0.05 and P = 0.001, respectively). CONCLUSION A negative biopsy does not confirm the absence of cancer in the corresponding site in the RP specimen in a sextant or 21-sample biopsy protocol and cannot be used as a prognostic element before RP. A positive biopsy does not always correspond with a tumour in the same zone of the RP specimen. When 21-sample biopsies are re-grouped in to six regions, the value of a positive biopsy increases. A positive biopsy corresponds thus to a tumour in the same region, rather than in precisely the same location. The results of this study could help in the biopsy protocol used for making surgical decisions, e.g. preserving the bladder neck or neurovascular bundles.