Evaluating residual tumor after neoadjuvant chemotherapy for muscle-invasive urothelial bladder cancer: diagnostic performance and outcomes using biparametric vs. multiparametric MRI

Abstract

Background: Neoadjuvant chemotherapy (NAC) before radical cystectomy is standard of care in patients with muscle-invasive bladder cancer (MIBC). Response assessment after NAC is important but suboptimal using CT. We assessed MRI without vs. with intravenous contrast (biparametric [BP] vs. multiparametric [MP]) for identifying residual disease on cystectomy and explored its prognostic role.

Methods: Consecutive MIBC patients that underwent NAC, MRI, and cystectomy between January 2000-November 2022 were identified. Two radiologists reviewed BP-MRI (T2 + DWI) and MP-MRI (T2 + DWI + DCE) for residual tumor. Diagnostic performances were compared using receiver operating characteristic curve analysis. Kaplan-Meier curves and Cox proportional-hazards models were used to evaluate association with disease-free survival (DFS).

Results: 61 patients (36 men and 25 women; median age 65 years, interquartile range 59-72) were included. After NAC, no residual disease was detected on pathology in 19 (31.1%) patients. BP-MRI was more accurate than MP-MRI for detecting residual disease after NAC: area under the curve = 0.75 (95% confidence interval (CI), 0.62-0.85) vs. 0.58 (95% CI, 0.45-0.70; p = 0.043). Sensitivity were identical (65.1%; 95% CI, 49.1-79.0) but specificity was higher in BP-MRI compared with MP-MRI for determining residual disease: 77.8% (95% CI, 52.4-93.6) vs. 38.9% (95% CI, 17.3-64.3), respectively. Positive BP-MRI and residual disease on pathology were both associated with worse DFS: hazard ratio (HR) = 4.01 (95% CI, 1.70-9.46; p = 0.002) and HR = 5.13 (95% CI, 2.66-17.13; p = 0.008), respectively. Concordance between MRI and pathology results was significantly associated with DFS. Concordant positive (MRI+/pathology+) patients showed worse DFS than concordant negative (MRI-/pathology-) patients (HR = 8.75, 95% CI, 2.02-37.82; p = 0.004) and compared to the discordant group (MRI+/pathology- or MRI-/pathology+) with HR = 3.48 (95% CI, 1.39-8.71; p = 0.014).

Conclusion: BP-MRI was more accurate than MP-MRI for identifying residual disease after NAC. A negative BP-MRI was associated with better outcomes, providing complementary information to pathological assessment of cystectomy specimens.

Keywords: Biparametric; Cystectomy; Magnetic resonance imaging; Multiparametric; Muscle-invasive bladder cancer; Neoadjuvant chemotherapy; Prognosis; Response assessment; Survival; Urothelial.

Fig. 1

Flowchart for patient selection

Fig. 2

Receiver operating characteristic (ROC) analysis comparing diagnostic performance of biparametric and multiparametric MRI for detecting residual tumor on cystectomy specimens after neoadjuvant chemotherapy. Biparametric MRI was superior to multiparametric MRI with corresponding areas under the ROC of 0.75 (95% confidence interval [CI], 0.62–0.88) and 0.58 (95% CI, 0.44–0.72), respectively

Fig. 3

Seventy-two-year old man with high grade muscle-invasive urothelial bladder cancer on transurethral resection. MRI performed after 3 cycles of neoadjuvant gemcitabine + cisplatin, showed residual focal wall thickening (arrow) in the anterior bladder wall on axial T2-weighted imaging (A). There was no abnormal high signal on axial diffusion-weighed imaging (B) but mild ill-defined enhancement was noted on sagittal post-contrast MRI (C). At radical cystectomy, there was a 0.5-cm focus of residual tumor in situ (ypTis). Patient was alive without recurrence at 792 days after surgery

Fig. 4

Fifty-five-year old woman with high grade muscle-invasive urothelial bladder cancer on transurethral resection. MRI performed after 4 cycles of neoadjuvant gemcitabine + carboplatin, showed an intermediate signal nodule (arrow) on T2-weighted imaging (A) with corresponding focal high signal on diffusion-weighed imaging (B) and early and strong enhancement on post-contrast MRI (C). At radical cystectomy, there was residual tumor with perivesical fat invasion (ypT3). Tumor recurred at the pelvic sidewall at 78 days after surgery and the patient subsequently died at 128 days after surgery

Fig. 5

Sixty-four-year old woman with high grade muscle-invasive urothelial bladder cancer and small cell variant histology on transurethral resection. MRI performed after 4 cycles of neoadjuvant etoposide + cisplatin, showed minimal thickening on axial T2-weighted imaging at the site of resected tumor (A), no increased signal on axial diffusion-weighted imaging (B) but focal early nodular enhancement on sagittal post-contrast MRI (C). This was considered a negative biparametric and positive multiparametric MRI. At radical cystectomy, there was no residual tumor (ypT0). Patient was alive without recurrence at 1048 days after surgery

Fig. 6

Kaplan-Meier survival curves for disease-free survival in patients who received neoadjuvant chemotherapy followed by cystectomy. The survival estimates between three subgroups based on concordance and discordance between MRI and pathology showed significant difference (p < 0.001)