Personalized Medicine and Imaging 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 (VolumeADC) and tumormeanADCvalue (ADCmean) are independent predictors of prostate tumorGleason score (GS). Experimental Design: Tumor volume andGSwere recorded fromwhole-mount histopathology for 131 men (median age, 60 years) who underwent endorectal diffusion-weightedMRI for local staging of prostate cancer before prostatectomy. VolumeADC and ADCmean 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 VolumeADC and ADCmean in discriminating tumors of GS 6 and GS 7. Results: Histopathology identified 116 tumor foci >0.5 mL. VolumeADC correlated significantly with histopathologic tumor volume (r1⁄40.683). The correlation increasedwith increasingGS (r1⁄40.453 forGS6 tumors;r1⁄40.643 forGS7 tumors;r1⁄40.980 forGS 8 tumors). BothVolumeADC (r1⁄40.286) andADCmean (r 1⁄4 0.309) correlated with GS. At univariate analysis, both VolumeADC (P 1⁄4 0.0325) and ADCmean (P 1⁄4 0.0033) could differentiate GS 1⁄4 6 from GS 7 tumor foci. However, at multivariate analysis, only ADCmean (P 1⁄4 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 VolumeADC and ADCmean, respectively, and 0.749 for both parameters combined. Conclusion: In patients with prostate cancer, ADCmean is an independent predictor of tumor aggressiveness, but VolumeADC is not. The latter parameter adds little to the ADCmean in predicting tumor GS.Clin Cancer Res; 20(14); 3705–11. 2014 AACR.