Objective: To evaluate the effect of the body mass index (BMI) as it relates to the predictive value of the preoperative prostate-specific antigen (PSA) level regarding the tumor volume at radical prostatectomy. Stage migration with the widespread use of PSA screening is well documented; however, the association between the PSA level and tumor volume is less defined. Additionally, the effect of obesity on the serum PSA level might cause relative hemodilution and account for the decreased predictive ability of the PSA level to determine the tumor volume in the modern era. Methods: We identified 14 293 patients who had undergone radical prostatectomy for prostate cancer from 1987 to 2007 and had a documented BMI. Using the clinicopathologic variables, we examined the relationship among the BMI, preoperative PSA level, and tumor volume at radical prostatectomy using multiple linear regression analysis. Results: An elevated BMI was associated with an increased pathologic Gleason score (P <.0001), increased tumor volume (P <.0001), and increased prostate size (P <.0001). The preoperative PSA level correlated significantly with the tumor volume (P <.0001). No significant correlation was found between the BMI and preoperative PSA level (P =.39). On multivariate analysis, controlling for the BMI, the preoperative PSA level remained a significant predictor of the tumor volume (P <.0001). The interaction between the preoperative PSA level and BMI in the prediction of the tumor volume was not statistically significant (P =.56), suggesting that the BMI does not affect the association between the PSA level and tumor volume. Conclusion: Our results have shown that the predictive ability of the PSA level for tumor volume is not affected by the BMI. There does not appear to be a need to correct the serum PSA level in relation to the BMI when used in preoperative prediction models of the tumor volume.
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