Abstract We present the proteomic profiling of 79 bladder cancers, including treatment‐naïve non‐muscle‐invasive bladder cancer (NMIBC, n = 17), muscle‐invasive bladder cancer (MIBC, n = 51), and neoadjuvant‐treated MIBC ( n = 11). Proteins were extracted from formalin‐fixed, paraffin‐embedded samples and analyzed using data‐independent acquisition, yielding &gt;8,000 quantified proteins. MIBC, compared to NMIBC, shows an extracellular matrix (ECM) and immune response signature as well as alteration of the metabolic proteome together with concomitant depletion of proteins involved in cell–cell adhesion and lipid metabolism. Neoadjuvant treatment did not consistently impact the proteome of the residual tumor mass. NMIBC presents two proteomic subgroups that correlate with histological grade and feature signatures of cell adhesion or lipid/DNA metabolism. Treatment‐naïve MIBC presents three proteomic subgroups with resemblance to the basal‐squamous, stroma‐rich, or luminal subtypes and signatures of metabolism, immune functionality, or ECM. The metabolic subgroup presents an immune‐depleted microenvironment, whereas the ECM and immune subgroups are enriched for markers of M2‐like tumor‐associated macrophages and dendritic cells. Markers for natural killer cells are exclusive for the ECM subgroup, and markers for cytotoxic T cells are a hallmark of the immune subgroup. Endogenous proteolysis is increased in MIBC alongside upregulation of matrix metalloproteases, including MMP‐14. Genomic panel sequencing yielded the prototypical profile of prevalent FGRF3 alterations in NMIBC and TP53 alterations in MIBC. Tumor–stroma interactions of MIBC were investigated by proteomic analysis of patient‐derived xenografts, highlighting specific tumor and stroma contributions to the matrisome and tumor‐induced stromal proteome phenotypes. © 2024 The Author(s). The Journal of Pathology published by John Wiley &amp; Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Proteomic analysis of non‐muscle invasive and muscle invasive bladder cancer highlights distinct subgroups with metabolic, matrisomal, and immune hallmarks and emphasizes importance of the stromal compartment