Multiparametric MRI for assessing residual tumors in patients with muscle-invasive bladder cancer after neoadjuvant treatment: a reliable tool for guiding bladder preservation.

Objective: To evaluate the clinical utility of multiparametric MRI in differentiating pathological stages (ypT0 vs ypT1-4) in patients with muscle-invasive bladder cancer (MIBCa) following neoadjuvant therapy (NAT).

Materials and methods: In this double-center cohort study, post-NAT multiparametric MRI in all consecutive patients who underwent surgery after NAT was analyzed. Two experienced radiologists independently evaluated the MRI features obtained after NAT. The post-NAT yT stage was assigned based on T2-weighted diffusion-weighted imaging (T2DWI) and on contrast-enhanced MRI scans. The diagnostic accuracies for distinguishing post-NAT ypT0 from ypT1-4 tumors with the two protocols were evaluated. Cohen's kappa (κ) statistics were used to evaluate the consistency between readers for the post-NAT yT stage.

Results: A total of 149 patients (mean age, 62 years ± 10 [SD]; 131 men) from two institutions were enrolled. The area under the receiver operating characteristic curve of the contrast-enhanced MRI protocol in predicting post-NAT ypT0 stage was 0.84 (95% CI: 0.77, 0.91), which was better than that of the T2DWI protocol (0.75; 95% CI: 0.67, 0.81; p = 0.002). The interobserver agreement was excellent for both the T2DWI protocol (κ = 0.89) and the contrast-enhanced MRI protocol (κ = 0.85).

Conclusions: Multiparametric MRI, particularly contrast-enhanced MRI, demonstrated superior accuracy in identifying ypT0 status following NAT in MIBCa, establishing it as an essential diagnostic tool for guiding bladder preservation in clinical decision-making.

Key points: Question Accurately identifying pathological complete response (ypT0) after NAT is essential for selecting bladder-preservation strategies, yet remains clinically challenging. Findings Post-treatment contrast-enhanced MRI accurately identified ypT0 status with an AUC of 0.84 and excellent inter-reader agreement, outperforming T2DWI. Clinical relevance Contrast-enhanced MRI is a reliable, non-invasive method for detecting complete tumor response after NAT, enabling better patient selection for bladder-sparing approaches and potentially improving quality of life.