Molecular Characterization of Residual Bladder Cancer after Neoadjuvant Pembrolizumab

Abstract

Background: In patients with muscle-invasive urothelial bladder cancer (MIBC), molecular alterations in immunotherapy-resistant tumors found at radical cystectomy (RC) remain largely unstudied.

Objective: To investigate the biology of pembrolizumab-resistant tumors in comparison to an RC cohort treated without any systemic therapy and a cohort of neoadjuvant chemotherapy (NAC)-treated tumors.

Design, setting, and participants: Transcriptome-wide expression profiling was performed on 26 RC samples from patients with ypT2-4 disease after pembrolizumab treatment, of which 22 had matched pretherapy samples. Unsupervised consensus clustering (CC) was performed to compare 26 post-pembrolizumab samples with 94 RC samples without neoadjuvant treatment and 21 samples collected from the former tumor bed of NAC-treated patients (scar tissue). Clusters were investigated for their biological and clinical characteristics and were compared to a cohort of post-NAC tumors (n = 133).

Outcome measurements and statistical analysis: Patient and tumor characteristics were compared between subgroups using χ² tests and two-sided Wilcoxon rank-sum tests. The primary endpoint was recurrence-free survival.

Results and limitations: Molecular subtyping of pre- and post-pembrolizumab samples revealed significant differences: only 36% of samples had a concordant subtype according to the consensus classifier. Unsupervised CC revealed three distinct post-pembrolizumab clusters (basal, luminal, and scar-like). A scar-like subtype was present in 50% of the post-pembrolizumab cases (n = 13) and expressed genes associated with wound healing/scarring. This subtype had higher luminal marker expression in the post-pembrolizumab setting compared to CC scar-like tumors from the other cohorts. Patients with the scar-like subtype showed favorable prognosis after systemic therapy, but not in the RC-only setting. The small numbers in each subgroup represents the major study limitation.

Conclusions: This study expands our understanding of the biology of pembrolizumab-resistant MIBC and provides a framework for defining molecular subtypes after treatment. The results further support the hypothesis that luminal-type tumors may be resistant to immunotherapy or that this treatment may select for, or induce, a luminal phenotype.

Patient summary: We carried out genetic analysis for bladder cancer tumors from patients who had received an immunotherapy agent called pembrolizumab and compared them to tumors treated with standard chemotherapy or just bladder removal. We found differences in gene expression between the treatment types and between tumor tissue from the same patient before and after treatment. These results may be helpful in personalizing therapy strategies for patients with bladder cancer.

Keywords: Biomarkers; Gene expression profiling; Muscle-invasive bladder cancer; Neoadjuvant immunotherapy; Pembrolizumab.