Cancer-Associated Fibroblasts (CAFs): Understanding Their Role in Tumor Progression, Metastasis and Therapy Resistance

 

Cancer-Associated Fibroblasts (CAFs): Understanding Their Role in Tumor Progression, Metastasis and Therapy Resistance

Introduction

Cancer is not driven by malignant cells alone. Within every tumor exists a complex ecosystem made up of immune cells, endothelial cells, extracellular matrix components, blood vessels, signaling molecules, and stromal cells that interact continuously with cancer cells. Among these stromal components, cancer-associated fibroblasts (CAFs) have emerged as important regulators of tumor development, progression, metastasis, and therapeutic response.

Fibroblasts are connective-tissue cells that normally contribute to tissue structure, wound healing, extracellular matrix organization, and tissue repair. However, in the tumor microenvironment, certain fibroblasts can become activated and acquire distinct functional properties. These activated stromal cells are commonly referred to as cancer-associated fibroblasts.

CAFs are increasingly recognized as dynamic components of the tumor microenvironment rather than passive structural cells. They can communicate with cancer cells through growth factors, cytokines, chemokines, extracellular matrix proteins, and other signaling molecules. Through these interactions, CAFs can influence tumor-cell proliferation, invasion, angiogenesis, immune regulation, metabolic adaptation, and resistance to cancer treatment.

Understanding CAF biology is particularly important as oncology moves toward more personalized approaches to cancer care. Tumors that appear similar based on their cancer-cell characteristics can have very different stromal environments. Characterizing the behavior and molecular features of CAFs may therefore provide additional information for understanding tumor heterogeneity and identifying potential therapeutic opportunities.

This article explores the biology of cancer-associated fibroblasts, their origins and subtypes, their role in tumor progression and metastasis, their influence on the immune microenvironment and therapy resistance, and their potential significance in precision oncology.

 

What Are Cancer-Associated Fibroblasts?

Cancer-associated fibroblasts are activated fibroblast-like stromal cells found within and around many solid tumors. They are part of the broader tumor microenvironment and interact with malignant cells as well as immune cells, endothelial cells, pericytes, and extracellular matrix components.

Normal fibroblasts play essential roles in maintaining tissue architecture. They produce and organize extracellular matrix proteins such as collagen and fibronectin and participate in tissue repair. During cancer development, persistent signals from tumor cells and other components of the tumor microenvironment can alter fibroblast behavior.

Activated CAFs can acquire properties that distinguish them from normal tissue fibroblasts. They may produce increased levels of extracellular matrix proteins, growth factors, inflammatory mediators, and enzymes involved in matrix remodeling.

Importantly, CAFs are not a single uniform population. Different tumors can contain distinct CAF populations with different molecular signatures and biological functions. Some CAF populations may promote tumor progression, while others may have context-dependent or potentially tumor-restraining effects.

This heterogeneity makes CAF biology both scientifically important and therapeutically challenging.

 

Where Do Cancer-Associated Fibroblasts Come From?

The origin of CAFs is complex and may vary between tumor types and individual patients. Research suggests that multiple cellular sources can contribute to the CAF population.

Potential sources include:

• Resident tissue fibroblasts
• Mesenchymal stromal cells
• Perivascular cells
• Mesenchymal cells undergoing phenotypic changes
• Other stromal populations influenced by tumor-derived signals

Cancer cells and inflammatory cells can release signaling molecules that promote fibroblast activation. Transforming growth factor beta (TGF-β), platelet-derived growth factor (PDGF), inflammatory cytokines, and other pathways have been associated with fibroblast activation and CAF development.

The local tissue environment also plays an important role. Hypoxia, mechanical stress, extracellular matrix changes, metabolic alterations, and chronic inflammation can contribute to CAF activation and functional specialization.

Because CAFs can arise through different mechanisms, their molecular characteristics may differ significantly between cancer types and even between different regions of the same tumor.

 

CAF Heterogeneity: Why One CAF Is Not the Same as Another

One of the most important developments in CAF research is the recognition that CAFs represent a heterogeneous population.

Researchers have identified different CAF states or subpopulations based on their gene-expression profiles, spatial distribution, signaling pathways, and functional behavior.

Some CAF populations are associated with strong extracellular matrix production and remodeling. Others may be more closely associated with inflammatory signaling, immune regulation, or interactions with cancer cells.

Commonly investigated CAF-associated markers include:

• Alpha-smooth muscle actin (α-SMA)
• Fibroblast activation protein (FAP)
• Platelet-derived growth factor receptors
• Fibroblast-specific protein-related markers
• Podoplanin and other context-dependent stromal markers

However, no single marker reliably identifies every CAF population across all cancer types.

This heterogeneity is one reason why therapeutic strategies aimed at eliminating all CAFs may produce unpredictable outcomes. A more precise approach may involve identifying specific CAF populations or signaling pathways that contribute to disease progression.

 

How CAFs Remodel the Extracellular Matrix

The extracellular matrix (ECM) is a three-dimensional network surrounding cells that provides structural support and influences cell behavior. CAFs are major regulators of ECM composition and organization.

Activated CAFs can produce and modify extracellular matrix components including:

• Collagen
• Fibronectin
• Proteoglycans
• Matrix-associated proteins
• Matrix-remodeling enzymes

Excessive ECM production can result in increased tissue stiffness and changes in the physical organization of the tumor microenvironment.

This altered matrix can influence cancer-cell migration, proliferation, invasion, and signaling.

CAFs can also produce matrix metalloproteinases and other enzymes that modify extracellular matrix structures. Such remodeling can create pathways through which malignant cells move into surrounding tissues.

Therefore, CAF-mediated ECM remodeling is not simply a structural process. It can actively contribute to tumor progression.

 

CAFs and Tumor Growth

CAFs can communicate with malignant cells through direct and indirect mechanisms.

They may release growth factors, cytokines, and other signaling molecules that support cancer-cell survival and proliferation. These signals can activate pathways involved in cell-cycle regulation, survival, metabolism, and adaptation to environmental stress.

The interaction between CAFs and cancer cells can create a feedback loop.

Cancer cells release signals that activate fibroblasts, while activated CAFs release factors that support cancer-cell growth and survival.

This continuous communication can contribute to the development of a tumor microenvironment that favors malignant progression.

 

CAFs and Angiogenesis

Growing tumors require nutrients and oxygen, creating pressure for the development of new blood vessels.

CAFs can contribute to angiogenesis by producing signaling molecules that influence endothelial cells and vascular development.

By supporting abnormal blood-vessel formation, CAFs may help tumors maintain growth and create pathways for cancer-cell dissemination.

However, tumor-associated blood vessels are often structurally abnormal. They can have irregular architecture and altered permeability, contributing to heterogeneous oxygen and nutrient distribution.

This can further modify the tumor microenvironment and reinforce interactions between CAFs, cancer cells, immune cells, and vascular components.

 

CAFs and Cancer Metastasis

Metastasis is one of the major challenges in cancer treatment. It involves the movement of cancer cells from the primary tumor to distant organs.

CAFs can contribute to metastatic progression by remodeling the extracellular matrix and producing signals that promote cancer-cell migration and invasion.

ECM remodeling may create physical pathways that facilitate cancer-cell movement. CAF-derived signaling molecules can also influence epithelial-to-mesenchymal transition-related processes and other cellular programs associated with invasion.

In addition, CAFs can contribute to the formation of supportive environments at metastatic sites.

The interaction between tumor cells and stromal cells is therefore important not only within the primary tumor but also during the metastatic process.

 

CAFs and the Tumor Microenvironment

The tumor microenvironment consists of multiple interacting components, including:

• Cancer cells
• Fibroblasts and CAFs
• Immune cells
• Endothelial cells
• Blood vessels
• Extracellular matrix
• Cytokines and growth factors
• Metabolic products

CAFs can influence several of these components simultaneously.

Their signaling activity can modify immune-cell behavior, vascular function, extracellular matrix organization, and cancer-cell phenotypes.

This makes CAFs important coordinators of tumor-microenvironment interactions.

Rather than acting independently, CAFs participate in a complex network in which changes in one cell population can affect the behavior of others.

 

CAFs and Immune Suppression

Cancer cells can evade immune surveillance through multiple mechanisms. CAFs may contribute to this immune-suppressive environment.

Certain CAF populations can produce cytokines and chemokines that influence immune-cell recruitment and function. CAF-mediated ECM remodeling may also create physical barriers that affect immune-cell movement through the tumor.

In some tumor environments, dense stromal structures may restrict the ability of immune cells to reach malignant cells effectively.

CAFs can also interact with immune-cell populations, potentially influencing macrophages, T cells, and other immune components.

These interactions are especially relevant to cancer immunotherapy because effective immune responses require immune cells to reach and recognize tumor cells.

 

CAFs and Cancer Immunotherapy

Immune checkpoint inhibitors and other immunotherapies have transformed the treatment of several cancers. However, many patients do not respond or eventually develop resistance.

The tumor stroma can be one factor contributing to these outcomes.

CAF-rich tumor environments may be associated with immune exclusion, altered T-cell activity, and immunosuppressive signaling. The extracellular matrix generated by CAFs may also influence the physical accessibility of tumor cells.

As a result, researchers are investigating whether targeting specific CAF populations or CAF-associated pathways could improve responses to immunotherapy.

Potential strategies include combining stromal-targeting approaches with immune checkpoint blockade or other immunotherapeutic strategies.

However, because CAFs are heterogeneous and can have different functions, therapeutic targeting requires careful biological characterization.

 

CAFs and Therapy Resistance

Therapy resistance remains one of the biggest challenges in oncology.

Cancer cells can develop resistance through genetic and non-genetic mechanisms, but the surrounding tumor microenvironment can also contribute.

CAFs may influence therapy resistance through several mechanisms:

• Altering extracellular matrix structure
• Activating survival signaling
• Modifying drug penetration
• Supporting cancer-cell adaptation
• Influencing immune responses
• Changing tumor metabolism
• Creating protective stromal niches

Dense extracellular matrix structures may reduce the penetration or distribution of certain therapeutic agents within tumors.

CAF-derived growth factors and cytokines may also activate signaling pathways that help cancer cells survive treatment-induced stress.

These mechanisms make CAFs an important area of research in efforts to overcome treatment resistance.

 

CAFs and Chemotherapy

Chemotherapy effectiveness can be influenced by the tumor microenvironment.

CAFs may contribute to chemotherapy resistance by altering extracellular matrix architecture and producing survival-promoting signals.

In some tumors, stromal barriers may affect the distribution of therapeutic compounds. CAF-derived signaling can also help cancer cells adapt to treatment pressure.

Researchers are therefore exploring combination strategies that address both malignant cells and supportive stromal mechanisms.

Rather than targeting CAFs indiscriminately, future approaches may focus on specific CAF populations or molecular pathways responsible for treatment resistance.

 

CAFs and Radiation Therapy

Radiotherapy is widely used in cancer treatment, but the tumor microenvironment can influence radiation response.

CAFs may affect radiation sensitivity through interactions with cancer cells, extracellular matrix remodeling, inflammatory signaling, and tissue-repair processes.

Radiation itself can also alter the tumor microenvironment, potentially affecting fibroblast activation and stromal signaling.

Understanding these bidirectional interactions may help researchers develop strategies to improve radiotherapy effectiveness while managing unwanted tissue responses.

 

CAFs and Tumor Metabolism

Cancer cells undergo metabolic changes to support rapid growth and survival. CAFs can influence this metabolic environment.

Through metabolic communication and secreted factors, CAFs may affect nutrient availability, energy production, oxidative stress responses, and other metabolic processes.

Some research has investigated metabolic coupling between cancer cells and stromal cells, in which metabolites produced or modified by one population influence another.

This area of research connects CAF biology with the broader field of cancer metabolism and may reveal additional therapeutic opportunities.

 

CAFs and Cancer Stem-Like Properties

Cancer stem-like cells are tumor-cell populations associated with self-renewal, tumor initiation, and treatment resistance.

The tumor microenvironment can influence cancer-cell plasticity and stem-like characteristics.

CAF-derived signals may contribute to the maintenance of cellular states associated with survival and therapy resistance.

This suggests that CAFs may indirectly support tumor heterogeneity by influencing cancer-cell behavior and adaptation.

Understanding these interactions could be important for developing strategies that prevent tumor recurrence after treatment.

 

CAFs and Tumor Stiffness

One visible consequence of CAF-mediated extracellular matrix remodeling is increased tissue stiffness.

Abnormal collagen deposition and matrix cross-linking can change the mechanical properties of tumors.

Mechanical signals can influence cancer-cell behavior through mechanotransduction pathways.

As tumors become mechanically altered, cancer cells may receive signals that promote proliferation, migration, and survival.

This creates another layer of interaction between tumor biology and the physical properties of the tumor microenvironment.

 

CAFs as Potential Biomarkers

Because CAFs have distinct molecular and spatial characteristics, they are being investigated as potential biomarkers.

Potential CAF-related biomarkers could help researchers understand:

• Tumor aggressiveness
• Stromal activity
• Treatment response
• Risk of metastasis
• Immune exclusion
• Therapy resistance

However, CAF biomarker development remains challenging because CAF populations are heterogeneous and marker expression can vary across tumor types.

Future biomarker strategies may combine multiple CAF markers with genomic, transcriptomic, proteomic, imaging, and clinical information.

 

CAFs and Precision Oncology

Precision oncology traditionally focuses on identifying molecular characteristics of cancer cells and matching patients with appropriate therapies.

However, increasing evidence suggests that the tumor microenvironment should also be considered.

Two patients with similar cancer-cell mutations may have different stromal environments and therefore different responses to treatment.

Integrating CAF-related information into precision oncology could provide a more comprehensive view of tumor biology.

Potentially useful data could include:

• CAF molecular signatures
• Spatial distribution of CAFs
• ECM characteristics
• Immune-cell composition
• Tumor genomic alterations
• Imaging features
• Treatment history
• Clinical outcomes

Combining these datasets may help researchers identify patient subgroups with distinct tumor-microenvironment characteristics.

 

Spatial Biology and CAF Research

Traditional tissue analysis may provide limited information about the spatial organization of CAFs.

New technologies such as spatial transcriptomics, multiplex imaging, and advanced digital pathology can help researchers investigate where specific CAF populations are located within tumors.

Spatial information can reveal whether CAFs are concentrated near cancer cells, blood vessels, immune-cell populations, or invasive tumor margins.

This information may be particularly valuable because CAF function can depend on its physical location within the tumor.

Spatial biology is therefore helping researchers move from simply asking "which cells are present?" to asking "where are these cells located and how are they interacting?"

 

Single-Cell Technologies and CAF Heterogeneity

Single-cell sequencing has provided new insights into the diversity of fibroblast populations.

Instead of analyzing all stromal cells as a single group, single-cell approaches can identify distinct cellular states and molecular programs.

Researchers can use these technologies to investigate:

• CAF subpopulations
• Gene-expression patterns
• Signaling pathways
• Cellular interactions
• Tumor-specific stromal states

These discoveries may help identify which CAF populations are associated with tumor progression and which may have different or potentially protective functions.

 

Artificial Intelligence in CAF Research

Artificial intelligence is increasingly being applied to digital pathology and cancer imaging.

AI algorithms can analyze large numbers of tissue images and identify patterns that may be difficult to recognize manually.

In CAF research, AI could potentially assist with:

• Identifying stromal regions
• Quantifying fibroblast-associated markers
• Mapping CAF distribution
• Analyzing extracellular matrix patterns
• Integrating pathology with clinical data
• Predicting treatment response

Combining AI with spatial biology and molecular profiling could help develop more comprehensive models of the tumor microenvironment.

 

Therapeutic Strategies Targeting CAFs

Researchers are investigating several approaches to target CAF biology.

1. CAF Depletion

One strategy involves reducing populations of tumor-promoting CAFs.

However, complete CAF depletion may not always be beneficial because some fibroblast populations may have tumor-restraining functions.

2. CAF Reprogramming

Instead of eliminating CAFs, researchers are exploring whether activated fibroblasts can be reprogrammed toward less tumor-supportive states.

3. Targeting CAF Signaling

Molecular pathways involved in CAF activation and communication are potential therapeutic targets.

4. Targeting Extracellular Matrix Remodeling

Interfering with excessive matrix production or remodeling may help reduce stromal barriers and tumor-supportive signaling.

5. Combination Therapy

CAF-targeting approaches may potentially be combined with chemotherapy, radiotherapy, targeted therapy, or immunotherapy.

The most effective strategy may depend on the CAF subtype and tumor context.

 

Why CAF-Targeted Therapy Is Challenging

Despite promising research, targeting CAFs presents several challenges.

First, CAFs are highly heterogeneous. A therapy that eliminates one tumor-promoting population could potentially affect other fibroblast populations with different functions.

Second, CAFs are involved in normal tissue biology and wound healing. Broad targeting could therefore create unwanted effects in healthy tissues.

Third, CAF characteristics vary between tumor types and individual patients.

Finally, the relationship between CAFs and cancer cells is dynamic. Treatment itself can alter the tumor microenvironment, potentially changing CAF behavior.

These challenges highlight the importance of developing highly selective and context-dependent approaches.

 

The Future of CAF Research

The future of CAF research will likely involve deeper integration of molecular biology, spatial analysis, computational methods, and clinical data.

Researchers are increasingly interested in understanding CAF states rather than treating CAFs as a single cell population.

Future studies may combine:

• Single-cell sequencing
• Spatial transcriptomics
• Multiplex imaging
• Proteomics
• Digital pathology
• Artificial intelligence
• Functional tumor models
• Clinical outcome data

Such approaches could help identify specific CAF populations associated with treatment response or resistance.

Another important direction is the development of patient-specific models that reproduce interactions between cancer cells and stromal components.

These models could support drug testing and help identify combinations that target both cancer cells and their supportive microenvironment.

 

CAFs in the Era of Personalized Cancer Treatment

Personalized cancer treatment is increasingly moving beyond a focus on tumor-cell mutations alone.

Cancer is a complex ecosystem in which malignant cells interact with surrounding tissues and other cell populations.

CAFs represent an important component of this ecosystem.

By studying CAF composition, spatial organization, molecular signaling, and interaction with immune and cancer cells, researchers may gain a deeper understanding of why tumors behave differently between patients.

In the future, CAF-related information could potentially complement genomic and clinical biomarkers to improve patient stratification and treatment selection.

 

Conclusion

Cancer-associated fibroblasts are emerging as important regulators of the tumor microenvironment. Through extracellular matrix remodeling, signaling, immune regulation, angiogenesis, metabolic interactions, and communication with malignant cells, CAFs can influence tumor progression, invasion, metastasis, and therapy resistance.

At the same time, CAF biology is highly complex. CAFs are not a single uniform population, and different CAF states can have different effects depending on tumor type, tissue context, disease stage, and treatment environment.

Advances in single-cell sequencing, spatial transcriptomics, multiplex imaging, digital pathology, and artificial intelligence are providing researchers with increasingly detailed views of CAF heterogeneity and function.

The future of CAF research may therefore depend on moving away from broad CAF elimination toward more precise strategies that identify and target specific tumor-promoting fibroblast states while preserving beneficial stromal functions.

As oncology continues to evolve toward personalized treatment, understanding the tumor microenvironment alongside cancer-cell biology could become increasingly important. Cancer-associated fibroblasts may ultimately represent not only important drivers of tumor behavior but also valuable biomarkers and therapeutic targets in the next generation of precision oncology.

These emerging developments highlight the importance of continued scientific collaboration and knowledge exchange among researchers, clinicians, oncologists, and healthcare professionals. The International Experts Summit on Oncology & Cancer Care (Oncology Summit-2027), taking place March 25–27, 2027, in Osaka, Japan, provides a global platform for experts to share research, discuss emerging advances, and explore innovative approaches shaping the future of cancer care and precision oncology.

 

Frequently Asked Questions

What are cancer-associated fibroblasts?

Cancer-associated fibroblasts are activated fibroblast-like cells found within the tumor microenvironment. They can influence tumor growth, extracellular matrix organization, immune responses, metastasis, and treatment resistance.

How are CAFs different from normal fibroblasts?

Normal fibroblasts primarily support tissue structure and repair, whereas CAFs can acquire altered molecular and functional characteristics in response to signals from tumors and the surrounding microenvironment.

Do all CAFs promote cancer?

No. CAFs are heterogeneous, and their effects can vary according to their molecular state, location, tumor type, and biological context. Some populations may promote tumor progression, while others may have different or potentially tumor-restraining functions.

How do CAFs contribute to metastasis?

CAFs can remodel the extracellular matrix, release signaling molecules, and influence cancer-cell migration and invasion. These activities can create conditions that support metastatic progression.

Can CAFs cause treatment resistance?

CAFs can contribute to therapy resistance through extracellular matrix remodeling, altered drug penetration, survival signaling, immune regulation, and interactions with cancer cells.

Can CAFs be targeted with cancer therapy?

Researchers are investigating CAF depletion, CAF reprogramming, signaling-pathway inhibition, extracellular-matrix targeting, and combination therapies. Because CAFs are heterogeneous, selective targeting is an important consideration.

What role do CAFs play in immunotherapy?

Certain CAF populations may contribute to immune exclusion and immunosuppressive tumor environments. Researchers are investigating whether targeting CAF-related mechanisms could improve responses to immunotherapy.

Can CAFs be used as cancer biomarkers?

CAF-associated molecular markers and spatial patterns are being investigated as potential biomarkers for tumor behavior, treatment response, and prognosis. More research is needed to establish clinically reliable CAF-based biomarkers.

How can AI help CAF research?

AI can analyze digital pathology images, quantify stromal features, identify spatial patterns, integrate molecular information, and potentially support prediction of treatment response.

Why are CAFs important for precision oncology?

CAFs are an important component of the tumor microenvironment. Integrating CAF characteristics with genomic, pathological, imaging, and clinical information could provide a more complete picture of individual tumor biology and potentially support more personalized treatment strategies.