Objective: The purpose of this study was to evaluate quantitative apparent diffusion coefficient (ADC) metrics for the downgrading of Gleason score (GS) 9 or 10 prostate cancer (PCa) diagnosed by means of nontargeted transrectal ultrasound-guided biopsy.
Materials and methods: Between 2012 and 2015, 30 men with a diagnosis of GS 9 or 10 PCa at nontargeted transrectal ultrasound-guided biopsy underwent 3-T multiparametric MRI before radical prostatectomy (RP). Two radiologists blinded to the histopathologic results independently assessed multiparametric MR images using Prostate Imaging Reporting and Data System (PI-RADS) version 2. Whole-lesion ADC mean, centile, and texture features were extracted from coregistered ADC and RP maps by a third blinded radiologist. Comparisons were performed by chi-square, multivariable logistic regression, and ROC analysis.
Results: Tumors were downgraded to intermediate risk (GS 4 + 3 [n = 7] and GS 3 + 4 [n = 2]) PCa in 30.0% (9/30) of men after RP. There were no statistically significant differences between groups with respect to age (p = 0.028), prostate-specific antigen level (p = 0.018), or clinical stage (p = 0.021). PI-RADS version 2 scores did not differ between groups (p = 0.035, p = 0.091) with moderate agreement (κ = 0.48). There were no differences in mean or centile ADC (p = 0.269-0.634) between the two groups. ADC entropy was significantly lower in downgraded tumors (5.542 ± 0.721 [SD] vs 8.089 ± 1.237, p < 0.001) with no difference in kurtosis or skewness (p = 0.133, p = 0.296). The ROC AUC for the diagnosis of downgrading was 0.93 (95% CI, 0.84-1.00) with sensitivity of 85.7% and specificity of 88.9% when entropy was less than 6.31.
Conclusion: ADC entropy was significantly lower in GS 9 and 10 tumors diagnosed by means of nontargeted transrectal ultrasound-guided biopsy that were eventually downgraded to intermediate risk (GS 7) after RP. ADC texture analysis may be useful for further risk stratification of PCa diagnosed at biopsy.
Keywords: Gleason score; entropy; high risk; multiparametric MRI; prostate cancer; texture analysis.