Evaluation of Apparent Diffusion Coefficient as a Predictor of Grade Reclassification in Men on Active Surveillance for Prostate Cancer

OBJECTIVE To evaluate the association between apparent diffusion coefficient (ADC) on initial multiparametric MRI (mpMRI) and biopsy grade reclassification (GR) to grade group (GG) ≥2 prostate cancer (CaP) in men on active surveillance (AS) with GG 1 CaP. METHODS We retrospectively identified 242 AS patients with reported ADC values on their initial mpMRI. ADC value from the index lesion was assessed as an independent predictor of GR using a Cox model. To ease clinical interpretation, we used a log-rank test to establish an ADC cutoff of 1128 × 10−6 mm2/s for Kaplan-Meier analysis. RESULTS Of the 242 men, 70 underwent GR following initial mpMRI, of which 26 (37%) had GR at the index lesion. There was no significant difference in the median interval between biopsies for men with and without GR (P >.9). Men with GR had significantly lower median ADC than those without GR (P = .01). In multivariable analysis adjusting for age, prostate-specific antigen density, and National Comprehensive Cancer Network risk group, a 100-unit decrease in ADC was associated with a 12% increase in the risk of GR (HR = 1.12, 95% CI: 1.01–1.22, P = .03). Two- and 4-year rates of freedom from GR were significantly lower for men with ADC CONCLUSION For AS patients, lower ADC on initial mpMRI index lesion is associated with increased risk of GR to GG ≥2 CaP and would be a useful component of multivariable risk prediction tools.