Relationship between prostate volume, prostate-specific antigen nadir, and biochemical control

Purpose: In patients treated with definitive three-dimensional conformal radiotherapy (3D-CRT) for localized prostatic adenocarcinoma, we sought to evaluate the relationship between pretreatment prostate gland volume and posttreatment prostate-specific antigen (PSA) nadir, as well as the relationship of prostate volume and PSA nadir with biochemical control (bNED). Two subgroups were studied: favorable (PSA <10 ng/mL, Gleason score 2-6, and T1-T2A) and unfavorable (one or more: PSA ≥10 ng/mL, Gleason score 7-10, T2B-T3). Methods and Materials: A total of 655 men (n = 271 favorable and 384 unfavorable) were treated with 3D-CRT alone between May 1989 and November 1997. All patients had information on prostate volume and a minimum follow-up of 24 months (median 56, range 24-126). Of the 655 men, 481 (n = 230 favorable and 251 unfavorable) remained bNED at time of analysis, with biochemical failure defined in accordance with the American Society for Therapeutic Radiology and Oncology consensus definition. Factors analyzed for predictors of bNED included pretreatment prostate volume, posttreatment PSA nadir, pretreatment PSA, palpation T stage, Gleason score, center of the prostate dose, and perineural invasion (PNI). We also analyzed pretreatment prostate volume and its correlation to prognostic factors. For bNED patients, the relationship between PSA nadir and prostate volume was evaluated. Results: On multivariate analysis, prostate volume (p = 0.04) and palpation T stage (p = 0.02) were the only predictors of biochemical failure in the favorable group. On multivariate analysis of the unfavorable group, pretreatment PSA (p <0.0001), Gleason score (p = 0.02), palpation T stage (p = 0.009), and radiation dose (p <0.0001) correlated with biochemical failure, and prostate volume and PNI did not. For all 481 bNED patients, a positive correlation between pretreatment volume and PSA nadir was demonstrated (p <0.0001). Subgroup analysis of the favorable and unfavorable patients also demonstrated a positive correlation between prostate volume and PSA nadir (p = 0.003 and p = 0.0002, respectively). Using multiple regression analysis, the following were found to be predictive of PSA nadir in all bNED patients: prostate volume (p <0.0001), pretreatment PSA (p <0.0001), palpation T stage (p = 0.0002), and radiation dose (p = 0.0034). Gleason score and PNI were not predictive. For the favorable group, palpation T stage (p = 0.0006), pretreatment PSA (p = 0.0083), prostate volume (p = 0.0186), and Gleason score (p = 0.0592) were predictive of PSA nadir, and PNI and radiation dose were not predictive. In the unfavorable group, prostate volume (p = 0.0024), radiation dose (p = 0.0039), pretreatment PSA (p = 0.0182), and palpation T stage (p = 0.0296) were predictive of PSA nadir, and Gleason score and PNI were not predictive. Conclusion: This report is the first demonstration that prostate volume is predictive of PSA nadir for patients who are bNED in both favorable and unfavorable subgroups. PSA nadir did not correlate with bNED status in the favorable patients, but it was strongly predictive in the unfavorable patients. Prostate gland volume was also predictive of bNED failure in the favorable but not the unfavorable group.