CALCULATING PROSTATE-CANCER VOLUME PREOPERATIVELY - THE DAMICO EQUATION AND SOME OTHER OBSERVATIONS

Purpose: The primary morphological determinants of cancer progression in the prostate are tumor volume and the percentage of Gleason grades 4 and/or 5 disease. To date the best estimate of cancer volume before therapy has been serum prostate specific antigen (PSA) with Pearson's correlation coefficient value of approximately 0.5. Recently it was re ported that prostate cancer volume calculated according to the formula , cancer specific serum PSA/amount of PSA leaking into the serum per c m.(3) of cancer, highly correlates with actual cancer volume (R = 0.98 ). Because there is a definite need for greater accuracy in estimating cancer volume before therapy, we attempt to confirm this proposed equ ation in our radical prostatectomy series. Materials and Methods: We a pplied this equation to the initial 318 men with peripheral zone cance r treated only with radical prostatectomy at our institution who were followed for a mean and median of greater than 5 years. Calculated pro state cancer volume was determined according to the aforementioned equ ation with minor modifications, and correlated with the actual cancer volume measured in radical prostatectomy specimens. Pearson's correlat ion coefficient and the coefficient of determination were calculated u sing a linear regression model. Calculated prostate cancer volume was also previously used to predict pathological stage pT3. We compared ca lculated prostate cancer volume, clinical stage, Gleason grade and pre operative serum PSA in logistic univariate and multivariate regression s to predict stage pT3 disease. Results: Overall correlations for calc ulated prostate cancer volume were R = 0.537 and R-2 = 0.289 (p <0.000 1), which are much less than those previously noted (R = 0.98 and R-2 = 0.96). AS in the original report, we also divided our 318 cases into the 4 cancer volume subgroups of 0.5 cm.(3) or less, 0.5 to 2.0, 2.0 to 4.0 and greater than 4.0 cm.(3) (R = 0.251, 0.288, 0.382 and 0.462, and R-2 = 0.063, 0.083, 0.146 and 0.213 alone respectively). There wa s an increasing trend for better R and R-2 values with increasing pros tate cancer volume. Calculated prostate cancer volume was less than 0. 5 cm.(3) in 156 of our 318 patients (49%) and less than 0 in 37 (11.6% ). In these cases serum PSA alone strongly correlated with calculated prostate cancer volume (R = 0.877 and R-2 = 0.77). Univariate analysis demonstrated statistical significance for prediction of stage pT3 dis ease, Gleason grade, clinical stage, serum PSA and calculated prostate cancer volume but multivariate analysis revealed statistical signific ance only for Gleason grade (p <0.0001) and clinical stage (p <0.0036) . Values for PSA and calculated prostate cancer volume were not signif icant (p = 0.0640 and 0.7920, respectively). Conclusions: Calculated p rostate cancer volume did not predict cancer volume in our 318 patient s who underwent radical prostatectomy. While we are uncertain how to i nterpret the excellent correlation of calculated prostate cancer volum e with PSA, we believe that this correlation strongly suggests that mo st predictive information of calcuated prostate cancer volume is relat ed to serum PSA. Importantly in our 318 patients serum PSA was a much stronger predictor of cancer volume than calculated prostate cancer vo lume. As expected, Gleason grade and clinical stage are excellent pred ictors of stage pT3 disease but not of serum PSA or calculated prostat e cancer volume.