Abstract 7642: Activated FAP+ cancer-associated fibroblasts in non-muscle invasive bladder cancer are associated with progression to muscle-invasive disease

Abstract The majority of patients with bladder cancer initially present with non-muscle-invasive disease (NMIBC). While NMIBC may be cured with transurethral resection +/- intravesical therapies, approximately 20% of patients develop progression to muscle-invasive bladder cancer (MIBC) which requires life-altering treatments such as cystectomy and has a high risk of lethal metastatic recurrence. Current risk stratification for NMIBC relies on clinicopathologic features that overlook the potential role of the tumor microenvironment (TME) in bladder cancer pathogenesis. We sought to delineate the stromal and immune landscape alterations within the TME upon bladder cancer progression and to identify TME-related features that could enhance current prognostic approaches. Analyzing by single-cell RNA sequencing and multiplexed imaging of 22 untreated NMIBC and MIBC specimens, coupled with publicly available datasets, we discovered significant transcriptional variability among cancer-associated fibroblasts (CAFs) and macrophages across patients. This inter-patient variability was attributable to the extensive remodeling of these cell types during cancer progression. Notably, a specific subset of CAF, characterized by ITGA8+F3+ markers, was found to be highly enriched in NMIBC lesions and transcriptionally related to sub-urothelial fibroblasts of the healthy bladder, whereas a FAP+ CAF subset enriched for core matrisome related genes was dominant in MIBC lesions. We developed a FAP+ CAF signature which was then projected onto a large public dataset of bulk-RNAseq data from patients with NMIBC demonstrating that the FAP+ CAF signature was significantly associated with progression to MIBC independently of contemporary risk stratification scores. The presence of FAP+ CAFs in a subset of NMIBC specimens was orthogonally validated using immunohistochemistry. Importantly, areas with FAP staining were observed in close contact with individual or small groups of tumor cells exhibiting an invasive phenotype and partial epithelial-mesenchymal transition, likely explaining the higher risk of progression to MIBC. Our study improves our understanding of fibroblasts remodeling during bladder cancer progression and highlights the potential of integrating CAF-derived biomarkers into NMIBC risk stratification models. Citation Format: Abdenour Abbas, Shrisha Maskey, Evan Cheng, Ziao Li, Koushik Ganesh, Sudeh Izadmehr, Serena Janho dit Hreich, Benjamin Demaille, Jeremy Mesple, Philemon Sirven, Clementine Krucker, Jacqueline Fontugne, Isabelle Bernard-Pierrot, Yves Allory, Miriam Merad, Julien Adam, John Sfakianos, Ephraim Kenigsberg, Matthew Galsky, Helene Salmon. Activated FAP+ cancer-associated fibroblasts in non-muscle invasive bladder cancer are associated with progression to muscle-invasive disease [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7642.