Quantitative Shear-Wave Elastography in Prostate Cancer: Lesion-Level Stiffness Thresholds and Association with Histopathological Aggressiveness

Background/Objectives: Quantitative shear-wave elastography (SWE) may characterize prostate lesions, but diagnostic thresholds and associations with tumor grade remain uncertain. We evaluated lesion-level thresholds for prostate cancer (PCa) and clinically significant PCa (csPCa) using mean (Emean) and maximum (Emax) Young’s modulus and examined associations with histological grade. Methods: This retrospective analysis of prospectively acquired SWE included 166 histopathologically mapped PCa foci from 132 men undergoing radical prostatectomy. Emean and Emax were measured in cancer foci and matched contralateral benign mirror regions using whole-mount histopathology-guided regions of interest. Receiver operating characteristic (ROC) analysis yielded Youden thresholds, with patient-level cluster bootstrap and out-of-bag internal validation. Adjusted ordinal models examined associations with International Society of Urological Pathology Grade Group (GG). Results: Mean lesion-to-mirror differences were 22.33 kilopascals (kPa) for Emean and 31.73 kPa for Emax. For PCa versus benign mirror tissue, areas under the ROC curve (AUCs) were 0.765 and 0.797, with respective thresholds of 54.5 and 75.5 kPa (p < 0.001 for the AUC difference). For csPCa (137 GG ≥ 2 foci) versus 29 GG1 lesions and 166 benign mirror tissues, AUCs were 0.750 and 0.771, with thresholds of 54.5 and 77.5 kPa (p = 0.010). In cancer-only comparisons (GG ≥ 2 versus GG1), discrimination was limited (Emean AUC 0.595, 95% CI 0.492–0.699; Emax AUC 0.583, 95% CI 0.478–0.685). Stiffness correlated positively with GG in unadjusted analyses, but neither absolute stiffness nor lesion-to-mirror differences were independently associated with GG after adjustment for lesion size, zone, and prostate volume; lesion size remained associated. Conclusions: SWE showed moderate discrimination in retrospectively mapped lesions, with a small advantage for Emax. Prospective external validation is required before these thresholds can be considered for clinical use.