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

Abstract

<div>Abstract<p><b>Purpose:</b> To investigate whether tumor volume derived from apparent diffusion coefficient (ADC) maps (Volume<sub>ADC</sub>) and tumor mean ADC value (ADC<sub>mean</sub>) are independent predictors of prostate tumor Gleason score (GS).</p><p><b>Experimental Design:</b> 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<sub>ADC</sub> and ADC<sub>mean</sub> 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<sub>ADC</sub> and ADC<sub>mean</sub> in discriminating tumors of GS 6 and GS ≥7.</p><p><b>Results:</b> Histopathology identified 116 tumor foci >0.5 mL. Volume<sub>ADC</sub> correlated significantly with histopathologic tumor volume (ρ = 0.683). The correlation increased with increasing GS (ρ = 0.453 for GS 6 tumors; ρ = 0.643 for GS 7 tumors; ρ = 0.980 for GS ≥8 tumors). Both Volume<sub>ADC</sub> (ρ = 0.286) and ADC<sub>mean</sub> (ρ = −0.309) correlated with GS. At univariate analysis, both Volume<sub>ADC</sub> (<i>P</i> = 0.0325) and ADC<sub>mean</sub> (<i>P</i> = 0.0033) could differentiate GS = 6 from GS ≥7 tumor foci. However, at multivariate analysis, only ADC<sub>mean</sub> (<i>P</i> = 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<sub>ADC</sub> and ADC<sub>mean</sub>, respectively, and 0.749 for both parameters combined.</p><p><b>Conclusion:</b> In patients with prostate cancer, ADC<sub>mean</sub> is an independent predictor of tumor aggressiveness, but Volume<sub>ADC</sub> is not. The latter parameter adds little to the ADC<sub>mean</sub> in predicting tumor GS. <i>Clin Cancer Res; 20(14); 3705–11. ©2014 AACR</i>.</p></div>