[The value of prostatic biopsy in tumor mapping].

OBJECTIVES

Prostatic biopsies, a diagnostic tool, are also used as prognostic elements before radical prostatectomy. Their sites within the prostatic gland constitute one of these prognostic criteria. The authors compared the site of positive prostatic biopsies with that of the tumour after radical prostatectomy in order to study the value of this prognostic factor and the way in which it can be improved.

MATERIAL AND METHODS

From 1988 to 1996, 166 localized prostatic tumours treated by radical prostatectomy were diagnosed by 6 systematized ultrasound-guided transrectal biopsies and 3 supplementary median biopsies performed from the base to the prostatic apex. The site of positive biopsies was compared to that of the tumour within the prostatic gland.

RESULTS

Of the 996 sextant biopsies performed, 331 (33%) were positive, i.e. 1.99 biopsies per prostate. 92 (19%) median biopsies were positive. 331 positive sextant biopsies corresponded to a tumour within the prostate with a specificity of 81.5%, a sensitivity of 39.4%, a positive predictive value (PPV) of 83.3%, a negative predictive value (NPV) of 36.4% and an accuracy of 52%. For 3 median biopsies, the sensitivity was 70.3%, the specificity was 91.6%, the PPV was 61.9%, the NPV was 94%, and the accuracy was 82%. The weight of the prostate (prostates less than and greater than 45 g), influenced these results, as PPV decreased from 90.8% to 76.1% while NPV increased from 32.9% to 37.8%.

CONCLUSION

Negative biopsies in a prostatic zone after 6 randomized biopsies do not exclude the presence of tumour in this zone and cannot be used as a prognostic element before radical prostatectomy for the therapeutic management. The presence of negative biopsies in a prostatic zone must be interpreted by taking the prostatic weight into account. 3 median biopsies are more accurate and less influenced by prostatic weight.