Tumor Volume and Prostate Specific Antigen: Implications for Early Detection and Defining a Window of Curability

Abstract

We attempted to determine the relationship between tumor volume and extent of localized prostate cancer, as well as the interrelationships of tumor volume with prostate specific antigen (PSA) level, grade and stage. Serial whole mount sections from 128 patients who underwent radical prostatectomy were analyzed using a computer assisted volumetric program. Statistical evaluations were performed using logistic and simple regression analyses. The median tumor volume for patients with organ confined disease was significantly lower than for those with extraprostatic extension (1.25 versus 2.94 cc, p < 0.001). A significant incidence (32%) of small volume cancers (0.51 to 1.5 cc) exhibited extraprostatic extension while that of extraprostatic disease increased to 66% for patients with tumor volumes greater than 1.5 cc (p < 0.001). Of men with clinically significant (greater than 0.5 cc, or Gleason score 7 or more) pathological stage B disease 31% had a serum PSA value of 4 ng./ml. or less. Multivariate regression analysis of tumor volume as a function of PSA, grade and stage demonstrated that log PSA had the strongest association with tumor volume. Goodness-of-fit analysis (coefficient of determination) revealed that only 40 to 50% of the PSA levels are explained by tumor volume. These data suggest that the window of curability for prostate cancer decreases significantly once the tumor grows to a volume greater than 1.5 cc, and that grade and tumor volume are more significantly related to stage than PSA.