The relationship between tumor volume and the number of positive cores in men undergoing multisite extended biopsy: implication for expectant management.

PURPOSE

We assessed the relationship between the number of positive cores obtained at extended biopsy and tumor volume in radical prostatectomy specimens as a tool for predicting the biological significance of prostate cancer from biopsy data.

MATERIALS AND METHODS

The study group included 207 men who were treated with radical prostatectomy without neoadjuvant therapy at our cancer center. All patients were diagnosed by systematic extended biopsy (10 or 11 cores) performed between 1997 and 2003. The variables analyzed were patient age, prostate specific antigen, clinical stage, biopsy Gleason score, maximum tumor length in a core, greatest percent of tumor in a core, total tumor length, total percent of tumor in all cores, positive core location, initial or repeat biopsy and prostate volume in subgroups based on the number of positive cores, that is group 1-1, group 2-2 and group 3-3 or more cores. Bivariate correlation analysis and multiple logistic regression analysis were used to determine the predictors of insignificant cancer.

RESULTS

The number of positive cores was significantly related to total tumor volume (r = 0.433, p <0.001). Insignificant prostate cancer (volume less than 0.5 cc and Gleason score 6 or less) was found in 21.7% of patients (45 of 207). The incidence of insignificant cancer was 42.5% (31 of 73 patients) in group 1, 16.4% (10 of 61) in group 2 and 5.5% (4 of 73) in group 3. There was a significant difference in the incidence of insignificant cancer among the subgroups (group 1 vs 2 p <0.001, group 1 vs 3 p <0.0001 and group 2 vs 3 p <0.05). The best model for predicting insignificant cancer in group 1 was the combination of tumor length less than 2 mm, Gleason score 3 + 4 or less and prostate volume greater than 50 cc with 83.9% sensitivity (26 of 31 patients) and 61.9% specificity (26 of 42).

CONCLUSIONS

The probability of insignificant cancer was directly related to the number of positive cores. Tumor length in a core, Gleason score and prostate volume significantly enhanced the prediction model for insignificant cancer in men with 1 positive core who underwent extended biopsy.