Inter- and intra-tumoural heterogeneity in cancer-associated fibroblasts of human pancreatic ductal adenocarcinoma

Fibrosis and cancer: A strained relationship

Tumors are characterized by extracellular matrix (ECM) deposition, remodeling, and cross-linking that drive fibrosis to stiffen the stroma and promote malignancy. The stiffened stroma enhances tumor cell growth, survival and migration and drives a mesenchymal transition. A stiff ECM also induces angiogenesis, hypoxia and compromises anti-tumor immunity. Not surprisingly, tumor aggression and poor patient prognosis correlate with degree of tissue fibrosis and level of stromal stiffness. In this review, we discuss the reciprocal interplay between tumor cells, cancer associated fibroblasts (CAF), immune cells and ECM stiffness in malignant transformation and cancer aggression. We discuss CAF heterogeneity and describe its impact on tumor development and aggression focusing on the role of CAFs in engineering the fibrotic tumor stroma and tuning tumor cell tension and modulating the immune response. To illustrate the role of mechanoreciprocity in tumor evolution we summarize data from breast cancer and pancreatic ductal carcinoma (PDAC) studies, and finish by discussing emerging anti-fibrotic strategies aimed at treating cancer.

Cancer-associated fibroblasts in cholangiocarcinoma

PURPOSE OF REVIEW

To give a state-of-art knowledge regarding cancer-associated fibroblasts (CAF) in cholangiocarcinoma (CCA) based both on direct evidence and studies on other desmoplastic cancers. High contingency of CAF characterizes CCA, a tumor with a biliary epithelial phenotype that can emerge anywhere in the biliary tree. Current treatments are very limited, the surgical resection being the only effective treatment but restricted to a minority of patients, whereas the remaining patients undergo palliative chemotherapy regimens. In cancer, CAF shape the tumor microenvironment, drive cancer growth and progression, and contribute to drug resistance. All these functions are accomplished through an interplay network between CAF and surrounding cells including tumor and other stromal cells, i.e. immune and endothelial cells.

RECENT FINDINGS

Several studies have pointed out the existence of CAF sub-populations carrying out several and opposite functions, cancer-promoting or cancer-restraining as shown in pancreatic cancer, another prototypic desmoplastic tumor in which heterogeneity of CAF is well demonstrated.

SUMMARY

New CAF functions are now emerging in pancreatic and breast cancers like the modulation of immune responses or tumor metabolism, opening new area for treatments.

Serotonin-RhoA/ROCK axis promotes acinar-to-ductal metaplasia in caerulein-induced chronic pancreatitis

The underlying molecular mechanisms of chronic pancreatitis (CP) developing into pancreatic ductal adenocarcinoma (PDAC) remain largely unknown. Here we show that the level of serotonin in mouse pancreatic tissues is upregulated in caerulein-induced CP mice. In vitro study demonstrates that serotonin promotes the formation of acinar-to-ductal metaplasia (ADM) and the activation of pancreatic stellate cells (PSCs), which results from the activation of RhoA/ROCK signaling cascade. Activation of this signaling cascade increases NF-κB nuclear translocation and α-SMA expression, which further enhance the inflammatory responses and fibrosis in pancreatic tissues. Intriguingly, quercetin inhibits both ADM lesion and PSCs activation in vitro and in vivo via its inhibitory effect on serotonin release. Our findings underscore the instrumental role of serotonin-mediated activation of RhoA/ROCK signaling pathway in development of PDAC from CP and highlight a potential to impede PDAC development by disrupting tumor-promoting functions of serotonin.

Fibroblast Heterogeneity in the Pancreatic Tumor Microenvironment

The poor prognosis for patients with pancreatic ductal adenocarcinoma (PDAC) impels an improved understanding of disease biology to facilitate the development of better therapies. PDAC typically features a remarkably dense stromal reaction, featuring and established by a prominent population of cancer-associated fibroblasts (CAF). Genetically engineered mouse models and increasingly sophisticated cell culture techniques have demonstrated important roles for fibroblasts in PDAC progression and therapy response, but these roles are complex, with strong evidence for both tumor-supportive and tumor-suppressive or homeostatic functions. Here, we review the recent literature that has improved our understanding of heterogeneity in fibroblast fate and function in this disease including the existence of distinct fibroblast populations, and highlight important avenues for future study. SIGNIFICANCE: Although the abundant stromal reaction associated with pancreatic cancer has long been appreciated, the functions of the CAF cells that establish this stromal reaction remain unclear. An improved understanding of the transcriptional and functional heterogeneity of pancreatic CAFs, as well as their tumor-supportive versus tumor-suppressive capacity, may facilitate the development of effective therapies for this disease.

Prognostic impact of tumour-infiltrating lymphocytes and cancer-associated fibroblasts in patients with pancreatic adenocarcinoma of the body and tail undergoing resection

BACKGROUND

The prognosis of patients with pancreatic cancer remains poor and novel therapeutic targets are required urgently. Treatment resistance could be due to the tumour microenvironment, a desmoplastic stroma consisting of cancer-associated fibroblasts and tumour-infiltrating lymphocytes (TILs). The aim of the study was to evaluate the prognostic value of TILs and cancer-associated fibroblasts (CAFs) in pancreatic cancer of the body and tail.

METHODS

Using tissue microarray from resected left-sided pancreatic cancer specimens, the immunohistochemistry of TILs (cluster of differentiation (CD) 45, CD3, CD4, FoxP3 and CD8), CAFs (vimentin and α-smooth muscle actin (αSMA)) and functional markers (PD-L1 and Ki-67) was examined, and the association with disease-free (DFS) and overall (OS) survival investigated using a computer-assisted quantitative analysis. Patients were classified into two groups, with low or high levels or ratios, using the 75th percentile value as the cut-off.

RESULTS

Forty-three patients were included in the study. Their median DFS and OS were 9 and 27 months respectively. A high CD4/CD3 lymphocyte ratio was associated with poorer DFS (8 months versus 11 months for a low ratio) (hazard ratio (HR) 2·23, 95 per cent c.i. 1·04 to 4·61; P = 0·041) and OS (13 versus 27 months respectively) (HR 2·62, 1·11 to 5·88; P = 0·028). A low αSMA/vimentin ratio together with a high CD4/CD3 ratio was correlated with poorer outcomes. No significant association was found between Ki-67, PD-L1 and survival.

CONCLUSION

In patients with resected left-sided pancreatic cancer, a tumour microenvironment characterized by a high CD4/CD3 lymphocyte ratio along with a low αSMA/vimentin ratio is correlated with poorer survival.

Targeting the Tumor Microenvironment in Colorectal Peritoneal Metastases

Peritoneal metastasis (PM) occurs in approximately one in four colorectal cancer (CRC) patients. The pathophysiology of colorectal PM remains poorly characterized. Also, the efficacy of current treatment modalities, including surgery and intraperitoneal (IP) delivery of chemotherapy, is limited. Increasingly, therefore, efforts are being developed to unravel the PM cascade and at understanding the PM-associated tumor microenvironment (TME) and peritoneal ecosystem as potential therapeutic targets. Here, we review recent insights in the structure and components of the TME in colorectal PM, and discuss how these may translate into novel therapeutic approaches aimed at re-engineering the metastasis-promoting activity of the stroma.

Stromal Features of the Primary Tumor Are Not Prognostic in Genetically Engineered Mice of Pancreatic Cancer

The Kras^G12D/+;LSL-Trp53^R172H/+;Pdx-1-Cre (KPC) mouse model is frequently employed for preclinical therapeutic testing, in particular in regard to antistromal therapies. Here, we investigate the prognostic implications of histopathological features that may guide preclinical trial design. Pancreatic tumor tissue from n = 46 KPC mice was quantitatively analyzed using immunohistochemistry and co-immunofluorescence for proliferation (Ki67), mitotic rate (phospho-Histone 3, PHH3), apoptosis (cleaved caspase-3, CC3), collagen content, secreted protein acidic and rich in cysteine (SPARC), hyaluronic acid (HA), and α-smooth muscle actin (α-SMA). Furthermore, mean vessel density (MVD), mean lumen area (MLA), grading, activated stroma index (ASI), and fibroblast-proliferation rate (α-SMA/Ki67) were assessed. Univariate analysis using the Kaplan–Meier estimator and Cox regression model for continuous variables did not show association between survival and any of the analyzed parameters. Spearman correlation demonstrated that desmoplasia was inversely correlated with differentiated tumor grade (ρ = −0.84). Ki67 and PHH3 synergized as proliferation markers (ρ = 0.54), while SPARC expression was positively correlated with HA content (ρ = 0.37). MVD and MLA were correlated with each other (ρ = 0.31), while MLA positively correlated with CC3 (ρ = 0.45). Additionally, increased MVD was correlated with increased fibroblast proliferation rate (α-SMA + Ki67; ρ = 0.36). Our pilot study provides evidence that individual histopathological parameters of the primary tumor of KPC mice are not associated with survival, and may hint at the importance of systemic tumor-related effects such as cachexia.

Vimentin Expression in Tumor Microenvironment Predicts Survival in Pancreatic Ductal Adenocarcinoma: Heterogeneity in Fibroblast Population

BACKGROUND

The tumor microenvironment, including cancer-associated fibroblasts (CAFs), plays various clinical roles in cancer growth. CAFs are a heterogeneous population and express a variety of mesenchymal markers. However, the clinical roles for CAFs expressing different markers in pancreatic ductal adenocarcinoma (PDAC) remain unknown.

METHODS

We reviewed 67 resected PDAC patients who had not received preoperative therapy. Each primary tumor was analyzed for vimentin and α-smooth muscle actin (α-SMA) expression by immunohistochemical and dual immunofluorescence staining.

RESULTS

There was no correlation between the percentage of cells expressing vimentin and α-SMA in the tumor stroma (Pearson's correlation coefficient: r = 0.171). Higher vimentin expression (p = 0.018) was associated with significantly shorter overall survival in PDAC patients. Using dual immunofluorescence staining, vimentin-positive CAFs were divided into two subpopulations: co-expression of α-SMA, and no co-expression of α-SMA. In PDAC, the level of co-expression had no effect on survival using univariate analysis (median survival time, 33.3 months for low co-expression vs. 18.2 months for high co-expression; log-rank, p = 0.143). However, multivariate analysis clarified that CAFs expressing vimentin alone was an independent predictor of poor survival (p = 0.014; hazard ratio, 2.305; 95% confidence interval, 1.181-4.497).

CONCLUSIONS

Vimentin-positive CAFs without co-expression of α-SMA were associated with poor survival in PDAC, and CAFs possessed molecular and functional heterogeneity in this disease.

Targeting of the Cancer-Associated Fibroblast-T-Cell Axis in Solid Malignancies

The introduction of a wide range of immunotherapies in clinical practice has revolutionized the treatment of cancer in the last decade. The majority of these therapeutic modalities are centered on reinvigorating a tumor-reactive cytotoxic T-cell response. While impressive clinical successes are obtained, the majority of cancer patients still fail to show a clinical response, despite the fact that their tumors express antigens that can be recognized by the immune system. This is due to a series of other cellular actors, present in or attracted towards the tumor microenvironment, including regulatory T-cells, myeloid-derived suppressor cells and cancer-associated fibroblasts (CAFs). As the main cellular constituent of the tumor-associated stroma, CAFs form a heterogeneous group of cells which can drive cancer cell invasion but can also impair the migration and activation of T-cells through direct and indirect mechanisms. This singles CAFs out as an important next target for further optimization of T-cell based immunotherapies. Here, we review the recent literature on the role of CAFs in orchestrating T-cell activation and migration within the tumor microenvironment and discuss potential avenues for targeting the interactions between fibroblasts and T-cells.

CAF Subpopulations: A New Reservoir of Stromal Targets in Pancreatic Cancer

Cancer-associated fibroblasts (CAFs) are one of the most significant components in the tumour microenvironment (TME), where they can perform several protumourigenic functions. Several studies have recently reported that CAFs are more heterogenous and plastic than was previously thought. As such, there has been a shift in the field to study CAF subpopulations and the emergent functions of these subsets in tumourigenesis. In this review, we explore how different aspects of CAF heterogeneity are defined and how these manifest in multiple cancers, with a focus on pancreatic ductal adenocarcinoma (PDAC). We also discuss therapeutic approaches to selectively target protumourigenic CAF functions, while avoiding normal fibroblasts, providing insight into the future of stromal targeting for the treatment of PDAC and other solid tumours.

Precision medicine in pancreatic cancer: treating every patient as an exception

Patients with pancreatic cancer have not benefited from recent improvements in overall survival brought about by precision medicine in other malignancies. This failure is not due to a dearth of precision-medicine research in pancreatic ductal adenocarcinoma (PDAC), the main type of pancreatic cancer. In fact, the stalled progress in precision therapies for this type of cancer is due to the absence of agents that are able to target the common genetic alterations in PDAC. Several studies have attempted to phenotypically stratify PDAC at the transcriptional level. However, the value of such classifications will only be revealed through prospective studies and, crucially, only after development of new treatment options for this disease. Therefore, it is essential to learn from breakthrough discoveries in other cancer types that could benefit subpopulations of patients with PDAC and convert them from ordinary to exceptional responders. Identifying these exceptional patients will help to bring PDAC in line with other cancer types in terms of availability of precision therapies. Thus, the true challenge to precision medicine for PDAC might be the poor consensus on which genetic and phenotypic alterations across the spectrum of this disease are actionable; not the absence of actionable variables themselves. To reach consensus, knowledge and tools must be developed and disseminated for individuals who provide pancreatic cancer care, to enable the real-time identification of exceptional patients, more precise subgroup classifications, and effective disease management strategies; all informed by immediate feedback from clinical outcome data.

Latest Advances in Targeting the Tumor Microenvironment for Tumor Suppression

The tumor bulk is composed of a highly heterogeneous population of cancer cells, as well as a large variety of resident and infiltrating host cells, extracellular matrix proteins, and secreted proteins, collectively known as the tumor microenvironment (TME). The TME is essential for driving tumor development by promoting cancer cell survival, migration, metastasis, chemoresistance, and the ability to evade the immune system responses. Therapeutically targeting tumor-associated macrophages (TAMs), cancer-associated fibroblasts (CAFs), regulatory T-cells (T-regs), and mesenchymal stromal/stem cells (MSCs) is likely to have an impact in cancer treatment. In this review, we focus on describing the normal physiological functions of each of these cell types and their behavior in the cancer setting. Relying on the specific surface markers and secreted molecules in this context, we review the potential targeting of these cells inducing their depletion, reprogramming, or differentiation, or inhibiting their pro-tumor functions or recruitment. Different approaches were developed for this targeting, namely, immunotherapies, vaccines, small interfering RNA, or small molecules.

Up-to-Date Tailored Systemic Treatment in Pancreatic Ductal Adenocarcinoma

Despite intensive research efforts, pancreatic ductal adenocarcinoma is still regarded as an aggressive and life-limiting malignancy. Combination chemotherapy regimens that underpin the current treatment approach in the advanced setting have led to incremental survival gains in recent years but have failed to confer patients with a median overall survival that exceeds 12 months from diagnosis. Research has since focussed on understanding the role and interplay between various components of the desmoplastic stroma and tumour microenvironment, in addition to developing targeted therapies based on molecular features to improve the prognosis associated with this malignancy. This review will summarise the available systemic treatment options and discuss potential methods to refine the resolution of patient selection to enhance responses to currently available therapies. Furthermore, it will explore newer approaches anticipated to come to the fore of future clinical practice, such as agents targeting the DNA damage response and tumour microenvironment as well as immunotherapy-based combinations.

Integrin-Mediated TGFβ Activation Modulates the Tumour Microenvironment

TGFβ (transforming growth factor-beta) is a pleotropic cytokine with contrasting effects in cancer. In normal tissue and early tumours, TGFβ acts as a tumour suppressor, limiting proliferation and inducing apoptosis. However, these effects are eventually abrogated by the loss or inactivation of downstream signalling within the TGFβ pathway, and in established tumours, TGFβ then acts as a tumour promotor through multiple mechanisms including inducing epithelial-to-mesenchymal transition (EMT), promoting formation of cancer-associated fibroblasts (CAFs) and increasing angiogenesis. TGFβ is secrereted as a large latent complex and is embedded in the extracellular matrix or held on the surface of cells and must be activated before mediating its multiple functions. Thus, whilst TGFβ is abundant in the tumour microenvironment (TME), its functionality is regulated by local activation. The αv-integrins are major activators of latent-TGFβ. The potential benefits of manipulating the immune TME have been highlighted by the clinical success of immune-checkpoint inhibitors in a number of solid tumour types. TGFβ is a potent suppressor of T-cell-mediated immune surveillance and a key cause of resistance to checkpoint inhibitors. Therefore, as certain integrins locally activate TGFβ, they are likely to have a role in the immunosuppressive TME, although this remains to be confirmed. In this review, we discussed the role of TGFβ in cancer, the role of integrins in activating TGFβ in the TME, and the potential benefits of targeting integrins to augment immunotherapies.

Cancer-associated fibroblasts-heroes or villains?

Cancer-associated fibroblasts (CAFs) were originally presumed to represent a homogeneous population uniformly driving tumorigenesis, united by their morphology and peritumoural location. Our understanding of CAFs has since been shaped by sophisticated in vitro and in vivo experiments, pathological association and, more recently, ablation, and it is now widely appreciated that CAFs form a group of highly heterogeneous cells with no single overarching marker. Studies have demonstrated that the CAF population contains different subtypes based on the expression of marker proteins with the capacity to promote or inhibit cancer, with their biological role as accomplices or adversaries dependent on many factors, including the cancer stage. So, while CAFs have been endlessly shown to promote the growth, survival and spread of tumours via improvements in functionality and an altered secretome, they are also capable of retarding tumorigenesis via largely unknown mechanisms. It is important to reconcile these disparate results so that the functions of, or factors produced by, tumour-promoting subtypes can be specifically targeted to improve cancer patient outcomes. This review will dissect out CAF complexity and CAF-directed cancer treatment strategies in order to provide a case for future, rational therapies.

Role of Cancer-Associated Fibroblast in Gastric Cancer Progression and Resistance to Treatments

Although the survival of gastric cancer (GC) patients has gradually improved, the outcomes of advanced GC patients remain unsatisfactory despite standard treatment with conventional chemotherapy or targeted agents. Several studies have shown that cancer-associated fibroblasts (CAFs), a major component of tumor stroma in GC, may have significant roles in GC progression and resistance to treatments. CAFs are a major source of various secreted molecules in the tumor microenvironment, which stimulate cancer cells and other noncancerous components of GC. Surprisingly, these factors could be involved in gastric carcinogenesis. Cytokines, including interleukin-6 and interleukin-11, or growth factors, such as fibroblast growth factor produced from CAFs, can directly activate GC cells and consequently lead to the development of an aggressive phenotype. Galectin-1 or hepatocyte growth factor can be involved in CAF-derived neovascularization in GC. In addition, recent studies showed that CAFs can affect tumor immunity through M2 polarization of tumor-associated macrophages. Finally, the current study aimed to introduce several inhibitory agents and evaluate their suppressive effects on CAFs in patients with GC progression. However, further studies are required to evaluate their safety and select appropriate patients for application in clinical settings.

Pharmacogenetics of treatments for pancreatic cancer

Introduction: Despite clinical efforts, pancreatic ductal adenocarcinoma (PDAC) has a dismal prognosis. The scarcity of effective therapies can be reflected by the lack of reliable biomarkers to adapt anticancer drugs prescription to tumors' and patients' features. Areas covered: Pharmacogenetics should provide the way to select patients who may benefit from a specific therapy that best matches individual and tumor genetic profile, but it has not yet led to gains in outcome. This review describes PDAC pharmacogenetics findings, critically reappraising studies on polymorphisms and -omics profiles correlated to response to gemcitabine, FOLFIRINOX, and nab-paclitaxel combinations, as well as limitations of targeted therapies. Further, we question whether personalized approaches will benefit patients to any significant degree, supporting the need of new strategies within well-designed trials and validated genomic tests for treatment decision-making. Expert opinion: A major challenge in PDAC is the identification of subgroups of patients who will benefit from treatments. Minimally-invasive tests to analyze biomarkers of drug sensitivity/toxicity should be developed alongside anticancer treatments. However, progress might fall below expectations because of tumor heterogeneity and clonal evolution. Whole-genome sequencing and liquid biopsies, as well as prospective validation in selected cohorts, should overcome the limitations of traditional pharmacogenetic approaches.

Human Pancreatic Carcinoma-Associated Fibroblasts Promote Expression of Co-inhibitory Markers on CD4+ and CD8+ T-Cells

Carcinoma-associated pancreatic fibroblasts (CAFs) are the major type of cells in the stroma of pancreatic ductal adenocarcinomas and besides their pathological release of extracellular matrix proteins, they are also perceived as key contributors to immune evasion. Despite the known relevance of tumor infiltrating lymphocytes in cancers, the interactions between T-cells and CAFs remain largely unexplored. Here, we found that CAFs isolated from tumors of pancreatic cancer patients undergoing surgical resection (n = 15) expressed higher levels of the PD-1 ligands PD-L1 and PD-L2 compared to primary skin fibroblasts from healthy donors. CAFs strongly inhibited T-cell proliferation in a contact-independent fashion. Blocking the activity of prostaglandin E₂ (PGE₂) by indomethacin partially restored the proliferative capacity of both CD4⁺ and CD8⁺ T-cells. After stimulation, the proportion of proliferating T-cells expressing HLA-DR and the proportion of memory T-cells were decreased when CAFs were present compared to T-cells proliferating in the absence of CAFs. Interestingly, CAFs promoted the expression of TIM-3, PD-1, CTLA-4 and LAG-3 in proliferating T-cells. Immunohistochemistry stainings further showed that T-cells residing within the desmoplastic stromal compartment express PD-1, indicating a role for CAFs on co-inhibitory marker expression also in vivo. We further found that PGE₂ promoted the expression of PD-1 and TIM-3 on T-cells. Functional assays showed that proliferating T-cells expressing immune checkpoints produced less IFN-γ, TNF-α, and CD107a after restimulation when CAFs had been present. Thus, this indicates that CAFs induce expression of immune checkpoints on CD4⁺ and CD8⁺ T-cells, which contribute to a diminished immune function.

Human Pancreatic Carcinoma-Associated Fibroblasts Promote Expression of Co-inhibitory Markers on CD4+ and CD8+ T-Cells

Carcinoma-associated pancreatic fibroblasts (CAFs) are the major type of cells in the stroma of pancreatic ductal adenocarcinomas and besides their pathological release of extracellular matrix proteins, they are also perceived as key contributors to immune evasion. Despite the known relevance of tumor infiltrating lymphocytes in cancers, the interactions between T-cells and CAFs remain largely unexplored. Here, we found that CAFs isolated from tumors of pancreatic cancer patients undergoing surgical resection (n = 15) expressed higher levels of the PD-1 ligands PD-L1 and PD-L2 compared to primary skin fibroblasts from healthy donors. CAFs strongly inhibited T-cell proliferation in a contact-independent fashion. Blocking the activity of prostaglandin E2 (PGE2) by indomethacin partially restored the proliferative capacity of both CD4+ and CD8+ T-cells. After stimulation, the proportion of proliferating T-cells expressing HLA-DR and the proportion of memory T-cells were decreased when CAFs were present compared to T-cells proliferating in the absence of CAFs. Interestingly, CAFs promoted the expression of TIM-3, PD-1, CTLA-4 and LAG-3 in proliferating T-cells. Immunohistochemistry stainings further showed that T-cells residing within the desmoplastic stromal compartment express PD-1, indicating a role for CAFs on co-inhibitory marker expression also in vivo. We further found that PGE2 promoted the expression of PD-1 and TIM-3 on T-cells. Functional assays showed that proliferating T-cells expressing immune checkpoints produced less IFN-γ, TNF-α, and CD107a after restimulation when CAFs had been present. Thus, this indicates that CAFs induce expression of immune checkpoints on CD4+ and CD8+ T-cells, which contribute to a diminished immune function.

Cancer-associated fibroblasts as abettors of tumor progression at the crossroads of EMT and therapy resistance

In the last decades, the role of the microenvironment in tumor progression and therapeutic outcome has gained increasing attention. Cancer-associated fibroblasts (CAFs) have emerged as key players among stromal cells, owing to their abundance in most solid tumors and their diverse tumor-restraining/promoting roles. The interplay between tumor cells and neighboring CAFs takes place by both paracrine signals (cytokines, exosomes and metabolites) or by the multifaceted functions of the surrounding extracellular matrix. Here, we dissect the most recent identified mechanisms underlying CAF-mediated control of tumor progression and therapy resistance, which include induction of the epithelial-to-mesenchymal transition (EMT), activation of survival pathways or stemness-related programs and metabolic reprogramming in tumor cells. Importantly, the recently unveiled heterogeneity in CAFs claims tailored therapeutic efforts aimed at eradicating the specific subset facilitating tumor progression, therapy resistance and relapse. However, despite the large amount of pre-clinical data, much effort is still needed to translate CAF-directed anti-cancer strategies from the bench to the clinic.