Prostate Elastography Distinguishes Cancer but Not Grade

Key Takeaways

• In a Polish prostatectomy cohort, histopathologically mapped prostate cancer foci were generally stiffer than paired benign regions in the opposite lobe.
• Emax discriminated cancer from paired benign tissue slightly better than Emean, a statistically significant difference.
• Among cancer foci alone, stiffness measures showed limited discrimination between GG1 and GG2 or higher.
• Stiffness correlated positively with grade before adjustment, but adjusted stiffness associations disappeared while the lesion-size association persisted.

For men with suspicious prostate regions, stiffness-based characterization poses two distinct questions: whether a region contains cancer and whether cancer in that region has a higher histologic grade. Transrectal shear-wave elastography (SWE) measures stiffness before biopsy, but tissue characterization and grading are not interchangeable tasks. Investigators compared acquired images with subsequent whole-mount histology to examine each question.

Investigators retrospectively reassessed prospectively acquired prebiopsy SWE in 132 biopsy-naive men with Prostate Imaging Reporting and Data System (PI-RADS) version 2.1 findings of at least 3 who underwent prostatectomy at one hospital in Wrocław, Poland. They matched 166 pathology-mapped cancer foci to 166 histologically benign contralateral mirror regions in archived images, using comparable Q-Box placements. Emean represented mean Young’s modulus and Emax maximum Young’s modulus. Clinically significant prostate cancer meant International Society of Urological Pathology (ISUP) Grade Group (GG) of at least 2. Its comparison group combined GG1 cancer with benign mirror tissue; a separate cancer-only comparison contrasted GG1 with GG2 or higher. Receiver operating characteristic (ROC) analysis generated internally selected Youden cutoffs, and grade models adjusted for lesion size, zone, and prostate volume.

Cancer foci were generally stiffer than their paired benign mirrors, although some were not. For cancer versus benign mirror tissue, the areas under the ROC curve (AUCs) were 0.765 for Emean and 0.797 for Emax. The Emax advantage was statistically significant but small: an AUC difference of 0.032 (95% confidence interval 0.016–0.047). These estimates describe discrimination between retrospectively matched sites.

The exploratory cancer-versus-mirror cutoffs were 54.5 kilopascals (kPa) for Emean and 75.5 kPa for Emax. Emax also edged Emean when clinically significant cancer was compared with a composite of GG1 cancer and benign tissue, but that comparison cannot establish grading performance within cancer alone.

In the cancer-only GG2-or-higher versus GG1 comparison, AUCs were 0.595 for Emean and 0.583 for Emax. Both measures correlated positively with grade before adjustment. After adjustment for lesion size, zone, and prostate volume, neither absolute stiffness nor lesion-minus-mirror stiffness differences remained independently associated with grade; lesion size remained associated.

These were unblinded, retrospectively pathology-guided matched-site measurements in a magnetic resonance imaging (MRI)-positive, biopsy-proven surgical cohort, not prospective lesion detection or estimates in independent cancer-negative patients. Foci smaller than 3 mm were not mapped, and bilateral foci without a benign contralateral mirror were excluded. Patient-cluster bootstrap out-of-bag analysis internally assessed the cutoff-selection procedure, not whether the specific cutoffs would transfer to other settings. The investigators did not establish SWE’s incremental performance beyond multiparametric MRI. Findings from this Polish cohort do not establish performance in the United States.

The authors characterized SWE as a possible measure for characterizing mapped prostate lesions rather than an independently established marker of histopathologic grade. They called for prospective external validation of the exploratory thresholds before their clinical performance can be established.

Clinician Questions

How were Emean and Emax calculated when a prostate cancer focus required multiple SWE Q-Boxes?

For histopathology-mapped prostate cancer foci requiring multiple nonoverlapping Q-Boxes, Emean was the arithmetic mean of the individual Q-Box mean Young’s modulus measurements, while Emax was the highest individual Q-Box maximum. Contralateral benign mirror regions used matching Q-Box numbers, diameters, and spatial arrangements.

Were SWE stiffness cutoffs tested separately in peripheral-zone and transition-zone prostate cancer lesions?

SWE analysis included peripheral- and transition-zone lesions and accounted for zone in adjusted grade models, but did not assess whether diagnostic cutoffs performed comparably across the two zones. The pooled exploratory cutoffs therefore do not establish zone-specific accuracy.

This content is intended for healthcare professionals for educational purposes. The article and its image were developed with AI assistance and reviewed by members of the ReachMD team prior to publication. Please refer to the original source linked for the complete and most up-to-date information.