Prostate MRI: Evaluating Tumor Volume and Apparent Diffusion Coefficient as Surrogate Biomarkers for Predicting Tumor Gleason Score

Purpose: To investigate whether tumor volume derived from apparent diffusion coefficient (ADC) maps (Volume(ADC)) and tumor mean ADC value (ADC(mean)) are independent predictors of prostate tumor Gleason score (GS). Experimental Design: Tumor volume and GS were recorded from whole-mount histopathology for 131 men (median age, 60 years) who underwent endorectal diffusion-weighted MRI for local staging of prostate cancer before prostatectomy. Volume(ADC) and ADC(mean) were derived from ADC maps and correlated with histopathologic tumor volume and GS. Univariate and multivariate analyses were performed to evaluate prediction of tumor aggressiveness. Areas under receiver-operating characteristics curves (AUC) were calculated to evaluate the performance of Volume(ADC) and ADC(mean) in discriminating tumors of GS 6 and GS >= 7. Results: Histopathology identified 116 tumor foci >0.5 mL. Volume(ADC) correlated significantly with histopathologic tumor volume (rho = 0.683). The correlation increased with increasing GS (rho = 0.453 for GS 6 tumors; rho = 0.643 for GS 7 tumors; rho = 0.980 for GS >= 8 tumors). Both Volume(ADC) (rho = 0.286) and ADC(mean) (rho = -0.309) correlated with GS. At univariate analysis, both Volume(ADC) (P = 0.0325) and ADC(mean) (P = 0.0033) could differentiate GS 6 from GS >= 7 tumor foci. However, at multivariate analysis, only ADC(mean) (P = 0.0156) was a significant predictor of tumor aggressiveness (i. e., GS 6 vs. GS >= 7). For differentiating GS 6 from GS >= 7 tumors, AUCs were 0.644 and 0.704 for Volume(ADC) and ADC(mean), respectively, and 0.749 for both parameters combined. Conclusion: In patients with prostate cancer, ADC(mean) is an independent predictor of tumor aggressiveness, but Volume(ADC) is not. The latter parameter adds little to the ADC(mean) in predicting tumor GS. (C)2014 AACR.