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Cholangiocarcinoma (CCA) comprises diverse tumors of the biliary tree and is characterized by late diagnosis, short-term survival, and chemoresistance. CCAs are mainly classified according to their anatomical location and include diverse molecular subclasses harboring inter-tumoral and intratumoral heterogeneity. Besides the tumor cell component, CCA is also characterized by a complex and dynamic tumor microenvironment where tumor cells and stromal cells crosstalk in an intricate network of interactions. Cancer-associated fibroblasts, one of the most abundant cell types in the tumor stroma of CCA, are actively involved in cholangiocarcinogenesis by participating in multiple aspects of the disease including extracellular matrix remodeling, immunomodulation, neo-angiogenesis, and metastasis. Despite their overall tumor-promoting role, recent evidence indicates the presence of transcriptional and functional heterogeneous CAF subtypes with tumor-promoting and tumor-restricting properties. To elucidate the complexity and potentials of cancer-associated fibroblasts as therapeutic targets in CCA, this review will discuss the origin of cancer-associated fibroblasts, their heterogeneity, crosstalk, and role during tumorigenesis, providing an overall picture of the present and future perspectives toward cancer-associated fibroblasts targeting CCA., (Copyright © 2023 American Association for the Study of Liver Diseases.)

Cancer-associated fibroblasts (CAFs) are one of the most abundant stromal cell type in the tumor microenvironment (TME) of intrahepatic cholangiocarcinoma (iCCA), where they are actively involved in cancer progression through a complex network of interactions with other stromal cells. The majority of the studies investigating CAFs in iCCA have focused their attention on CAF tumor-promoting roles, remarking their potential as therapeutic targets. However, indiscriminate targeting of CAFs in other desmoplastic tumors has ended in failure with no effects or even accelerated cancer progression and reduced survival, indicating the urgent need to better understand the nuances and functions of CAFs to avoid deleterious effects. Indeed, recent single cell RNA sequencing studies have shown that heterogeneous CAF subpopulations coexist in the same tumor, some promoting- and other restricting- tumor growth. Moreover, recent studies have shown that in iCCA, diverse CAF subtypes interact differently with the cells of the TME, suggesting that CAFs may dynamically change their phenotypes during tumor progression, a field that remains uninvestigated. The characterization of heterogenous CAF subpopulations and their functionality, will provide a feasible and safer approach to facilitate the development of new therapeutic approaches aimed at targeting CAFs and their interactions with other stromal cells in the TME rather than solely tumor cells in iCCA. Here, we discuss the origin of CAFs, as well as their heterogeneity, plasticity, mechanisms and targeting strategies to provide a brief snapshot of the current knowledge in iCCA., Competing Interests: Conflict of interest A.R., S.B. and S.A. have no financial or personal disclosures., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Cancer-associated fibroblasts (CAF) are a poorly characterized cell population in the context of liver cancer. Our study investigates CAF functions in intrahepatic cholangiocarcinoma (ICC), a highly desmoplastic liver tumor. Genetic tracing, single-cell RNA sequencing, and ligand-receptor analyses uncovered hepatic stellate cells (HSC) as the main source of CAF and HSC-derived CAF as the dominant population interacting with tumor cells. In mice, CAF promotes ICC progression, as revealed by HSC-selective CAF depletion. In patients, a high panCAF signature is associated with decreased survival and increased recurrence. Single-cell RNA sequencing segregates CAF into inflammatory and growth factor-enriched (iCAF) and myofibroblastic (myCAF) subpopulations, displaying distinct ligand-receptor interactions. myCAF-expressed hyaluronan synthase 2, but not type I collagen, promotes ICC. iCAF-expressed hepatocyte growth factor enhances ICC growth via tumor-expressed MET, thus directly linking CAF to tumor cells. In summary, our data demonstrate promotion of desmoplastic ICC growth by therapeutically targetable CAF subtype-specific mediators, but not by type I collagen., Competing Interests: Declaration of interests A.C. is founder, equity holder, and consultant of DarwinHealth. Columbia University is an equity holder in DarwinHealth., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Cancer-associated fibroblasts (CAF) may exert tumor-promoting and tumor-suppressive functions, but the mechanisms underlying these opposing effects remain elusive. Here, we sought to understand these potentially opposing functions by interrogating functional relationships among CAF subtypes, their mediators, desmoplasia, and tumor growth in a wide range of tumor types metastasizing to the liver, the most common organ site for metastasis. Depletion of hepatic stellate cells (HSC), which represented the main source of CAF in mice and patients in our study, or depletion of all CAF decreased tumor growth and mortality in desmoplastic colorectal and pancreatic metastasis but not in nondesmoplastic metastatic tumors. Single-cell RNA-Seq in conjunction with CellPhoneDB ligand-receptor analysis, as well as studies in immune cell-depleted and HSC-selective knockout mice, uncovered direct CAF-tumor interactions as a tumor-promoting mechanism, mediated by myofibroblastic CAF-secreted (myCAF-secreted) hyaluronan and inflammatory CAF-secreted (iCAF-secreted) HGF. These effects were opposed by myCAF-expressed type I collagen, which suppressed tumor growth by mechanically restraining tumor spread, overriding its own stiffness-induced mechanosignals. In summary, mechanical restriction by type I collagen opposes the overall tumor-promoting effects of CAF, thus providing a mechanistic explanation for their dual functions in cancer. Therapeutic targeting of tumor-promoting CAF mediators while preserving type I collagen may convert CAF from tumor promoting to tumor restricting.