Tumor Microenvironment (TME) in Cancer: CAFs, Hypoxia, Hot vs Cold Tumors, Immunotherapy & Treatment Resistance (2026

Cancer Advisor  |  Updated September 19, 2026

The tumor microenvironment (TME) is the biological ecosystem surrounding a tumor. It includes immune cells, cancer-associated fibroblasts (CAFs), blood and lymphatic vessels, extracellular matrix, signaling molecules, nutrients, metabolites, oxygen gradients and physical conditions such as tissue stiffness, acidity and abnormal interstitial pressure.

Modern oncology increasingly recognizes that cancer is not simply a collection of malignant cells. Tumor cells continuously interact with their surrounding tissue, while the surrounding tissue can influence tumor growth, invasion, metastasis, immune surveillance, drug delivery and treatment response. The National Cancer Institute defines the TME broadly as the normal cells, molecules and blood vessels surrounding and feeding a tumor, and notes that tumors can change their microenvironment while the microenvironment can influence how tumors grow and spread.

This makes the TME a critical bridge between several major areas of cancer research: immunotherapy, cancer metabolism, precision oncology, stromal biology, angiogenesis, drug delivery, metastasis and treatment resistance.

Important: TME biology is highly cancer-specific and rapidly evolving. A mechanism demonstrated in a cell line or animal model does not automatically translate into a useful human treatment. This article distinguishes established clinical concepts from emerging and investigational strategies. It is educational information, not individualized medical advice.

Quick answer: The tumor microenvironment can help determine whether immune cells can reach a tumor, recognize it, remain functional, and whether drugs can penetrate the tissue effectively. CAF-rich stroma, abnormal blood vessels, hypoxia, suppressive immune cells and metabolic conditions can all contribute to treatment resistance. This is why increasingly sophisticated oncology research is moving beyond a single mutation or single biomarker toward a multidimensional model of tumor cells + immune state + stroma + vasculature + metabolism + spatial biology + treatment history.

In this article

1. What Is the Tumor Microenvironment?
2. The Major Components of the TME
3. The Tumor Immune Microenvironment
4. Cancer-Associated Fibroblasts and the Desmoplastic Shield
5. Tumor Blood Vessels and Vascular Dysfunction
6. Hypoxia and HIF Signaling
7. The Metabolic TME
8. Hot, Cold, Immune-Excluded and Immunosuppressive Tumors
9. TME and Immunotherapy
10. How the TME Contributes to Treatment Resistance
11. TME Biomarkers and Testing
12. Can the TME Be Targeted?
13. Repurposed Drugs and Supplements: What the Evidence Actually Shows
14. The TME in a Systems-Oncology Framework
15. What TME Analysis Means for a Patient
16. TME and the Cancer Treatment Resistance Atlas
17. Where TME Research Is Going
18. Key Takeaways
19. Frequently Asked Questions
20. References

1. What Is the Tumor Microenvironment?

The TME is the local biological environment in and around a tumor. It contains malignant cells, but also a large population of non-malignant cells and structures that can influence cancer behavior.

Communication within the TME occurs through cell-to-cell contact, cytokines, chemokines, growth factors, extracellular matrix proteins, metabolic substrates and waste products, oxygen gradients, acid-base changes, vascular signals and mechanical forces.

Figure 1. The ecosystem of systems oncology: genetics, metabolism, immunity, and the tumor microenvironment as an interconnected network rather than a static lesion.

The result is a dynamic ecosystem rather than a static "shell" around a tumor. Cancer cells alter their environment by consuming nutrients, changing extracellular matrix, releasing signaling molecules, recruiting immune and stromal cells and stimulating abnormal blood-vessel growth. Those surrounding cells can then send signals back to the cancer.

Tumor cells → reshape the microenvironment → microenvironment alters tumor behavior → treatment pressure → ecological adaptation → resistance

The NCI's definition is useful because it emphasizes the two-way relationship: tumors can change their microenvironment, and the microenvironment can affect tumor growth and spread.

2. The Major Components of the TME

There is no single "tumor microenvironment." The TME differs between cancer types, between patients with the same cancer, between primary and metastatic lesions, and even between different regions of the same tumor.

Component	Examples	Why It Matters
Immune cells	T cells, B cells, NK cells, dendritic cells, macrophages, MDSCs, Tregs	Can promote or suppress anti-tumor immunity depending on cell state and context.
Cancer-associated fibroblasts	Activated fibroblast populations, including heterogeneous CAF subsets	Remodel extracellular matrix and can influence immune exclusion, signaling and tissue mechanics.
Extracellular matrix	Collagen, fibronectin, laminins, hyaluronan and other matrix proteins	Provides structure and biochemical/mechanical signals and can contribute to physical barriers.
Endothelial and vascular cells	Tumor-associated endothelial cells and abnormal vessels	Affects perfusion, oxygen delivery, drug exposure and immune-cell trafficking.
Metabolites	Lactate, adenosine, kynurenine, glucose and amino acids	Can create metabolic competition and alter immune-cell function.
Physical environment	Hypoxia, acidity, tissue stiffness and interstitial pressure	Can affect signaling, immune activity and movement of therapeutic agents.

3. The Tumor Immune Microenvironment

The immune compartment of the TME is often called the tumor immune microenvironment (TIME). It is a major determinant of whether an immune response develops and whether that response remains effective.

The important question is not simply, "Are immune cells present?" Researchers increasingly examine which cells are present, where they are located, what state they are in, and whether they can actually function.

Immune cells that may matter

CD8+ T cells can directly kill tumor cells when appropriately activated. CD4+ T cells help coordinate immune responses. Natural killer cells can recognize and kill certain abnormal cells. Dendritic cells help present antigens and initiate adaptive immunity.

Other populations can suppress or reshape immunity. These include regulatory T cells, myeloid-derived suppressor cells (MDSCs) and distinct tumor-associated macrophage (TAM) states.

The biology is more complicated than labeling all macrophages or fibroblasts as "bad." Both immune and stromal populations are heterogeneous, and their effects depend on phenotype, location and signaling context.

4. Cancer-Associated Fibroblasts and the Desmoplastic Shield

Cancer-associated fibroblasts (CAFs) are stromal cells that become altered or activated within tumors. They can produce extracellular matrix components, remodel tissue structure and participate in signaling between malignant, immune and vascular cells.

Some tumors develop extensive fibroinflammatory tissue known as desmoplasia. This is especially prominent in pancreatic ductal adenocarcinoma (PDAC), although stromal reactions occur in many other malignancies.

How a dense stromal environment may interfere with treatment

A collagen-rich matrix can change tissue stiffness and architecture. Together with abnormal vessels and elevated interstitial pressure, this may reduce effective penetration or distribution of systemic therapies in some tumors.

The same environment may also influence immune access. T cells can accumulate around a tumor without effectively entering tumor nests, producing an immune-excluded phenotype.

This helps explain why the popular phrase "desmoplastic shield" is useful as a metaphor but incomplete as biology. The stroma is not simply a wall that should always be destroyed.

The stromal-normalization concept: research increasingly asks whether certain stromal components can be reprogrammed or normalized rather than indiscriminately eliminated. Some fibroblast populations can have tumor-restraining functions in experimental systems, meaning that wholesale stromal depletion can produce unexpected effects.

This distinction is particularly important in pancreatic cancer. A major 2025 review in Nature Reviews Clinical Oncology described the PDAC TME as a major barrier to systemic therapy and circulating immune cells, while emphasizing the heterogeneity of fibroblast and extracellular-matrix populations.

Nature Reviews Clinical Oncology: The tumour microenvironment in pancreatic cancer

5. Tumor Blood Vessels and Vascular Dysfunction

Tumor-associated blood vessels are often structurally and functionally abnormal. They may be tortuous, leaky, irregularly distributed and inefficient at delivering oxygen uniformly.

This matters for two separate reasons.

First, abnormal perfusion can contribute to areas with low oxygen and poor drug exposure. Second, vascular dysfunction can alter immune-cell trafficking into tumors.

This has led to the concept of vascular normalization: rather than simply eliminating blood vessels, researchers investigate whether carefully modulating abnormal vasculature can improve perfusion and immune access.

Again, the concept is not equivalent to a universally effective clinical treatment. The effect of vascular manipulation depends on the cancer type, drug, dose, treatment combination and biological context.

6. Hypoxia and HIF Signaling

Hypoxia means low oxygen availability. It is common in many solid tumors because rapidly growing tissue can outpace the ability of abnormal vessels to provide oxygen evenly.

Cells respond to low oxygen through signaling pathways involving hypoxia-inducible factors (HIFs). HIF signaling can influence glycolysis, angiogenesis, survival, extracellular-matrix remodeling, metastasis and immune-cell function.

Hypoxic Effect	Potential Consequence
HIF activation	Changes transcriptional programs that help cells adapt to low oxygen.
Greater glycolysis	Can increase glucose use and lactate production.
Angiogenic signaling	Can promote further abnormal blood-vessel formation.
Metabolic stress	Can intensify competition for nutrients and alter immune function.
Immune remodeling	May impair some T-cell and NK-cell functions and favor suppressive populations.
Resistance biology	Can contribute to reduced effectiveness of selected therapies through multiple pathways.

Hypoxia is therefore not simply "low oxygen." It is a signaling state that can connect metabolism, vascular biology and immune regulation.

7. The Metabolic TME: Glucose, Lactate, Adenosine and Nutrients

Tumors exist within a metabolically constrained environment. Cancer cells, immune cells and stromal cells all require nutrients and energy, creating both competition and cooperation.

Glucose

Highly glycolytic tumors can consume large amounts of glucose. Activated immune cells also require glucose and other substrates to maintain proliferation and effector functions. Nutrient competition can therefore influence the ability of immune cells to remain functional.

Lactate

High glycolytic activity can increase lactate production and export. Lactate is more than a metabolic waste product: it can act as a signaling and metabolic molecule within the TME.

Research has associated high lactate concentrations with impaired functions of certain immune effector cells and with immunosuppressive tumor states. However, lactate biology is context dependent, and lactate can also serve as a metabolic substrate.

Adenosine

Adenosine is another important immunoregulatory metabolite. High extracellular adenosine signaling can suppress aspects of anti-tumor immune activity, making the adenosine pathway an active area of immuno-oncology research.

Kynurenine and amino-acid metabolism

Tryptophan metabolism and other amino-acid pathways can influence immune-cell state. The larger lesson is that immune suppression is sometimes metabolic as well as receptor-mediated.

This is one reason the TME sits at the intersection of metabolic oncology and immunotherapy.

Explore the Cancer Advisor Metabolic Oncology Framework

8. Hot, Cold, Immune-Excluded and Immunosuppressive Tumors

The terms "hot" and "cold" are useful shorthand for describing broad immune states, but they are not formal universal diagnoses.

Contemporary research increasingly distinguishes at least four overlapping states: immune-inflamed (hot), immune-desert (cold), immune-excluded, and strongly immunosuppressive.

Immune State	Typical Description	Common Biological Challenge
Inflamed / "Hot"	Substantial immune-cell infiltration with evidence of an existing immune response.	T cells may still be exhausted or suppressed by checkpoints and other mechanisms.
Immune-desert / "Cold"	Few effective immune cells within the tumor.	There may be little pre-existing anti-tumor immunity available to reactivate.
Immune-excluded	Immune cells are present around the tumor but have limited penetration into tumor nests.	Stroma, extracellular matrix, chemokine signaling and abnormal vasculature can restrict access.
Immunosuppressive	Immune cells are present but local signaling strongly suppresses effective anti-tumor function.	Tregs, MDSCs, macrophage states, checkpoints and metabolic suppression may coexist.

A 2024 review in Signal Transduction and Targeted Therapy emphasized that the traditional hot-versus-cold binary is too simplistic and highlighted immune-desert, immune-excluded and inflamed patterns together with tumor genetics and other TME factors.

Wu et al. Cold and hot tumors: from molecular mechanisms to targeted therapy  |  PubMed

Importantly, a single tumor can contain multiple immune niches. One region may be inflamed while another is hypoxic, fibrotic or immune-excluded.

9. The TME and Cancer Immunotherapy

Immune checkpoint inhibitors targeting pathways such as PD-1, PD-L1 and CTLA-4 have transformed treatment for multiple cancers. But checkpoint blockade removes only selected inhibitory signals. It does not guarantee that a T cell can reach the tumor, recognize it, remain functional and kill the malignant cell.

TME Barrier	How It May Affect Immunotherapy
Low immune infiltration	There may be too few effective T cells present to reactivate.
Checkpoint signaling	Inhibitory pathways can reduce T-cell function.
Tregs	May actively suppress local immune responses.
MDSCs	Can suppress T-cell and NK-cell activity.
TAMs	Some macrophage states can reinforce immunosuppressive signaling.
Dense CAF-rich stroma	Can contribute to immune exclusion and abnormal tissue structure.
Abnormal vasculature	Can interfere with immune trafficking and perfusion.
Hypoxia	Can alter immune-cell function and tumor metabolism.
Lactate / adenosine	Can suppress aspects of immune-cell metabolism and effector function.

This helps explain why PD-L1 alone does not capture the entire immune landscape. Depending on the cancer, clinicians may also consider MSI/MMR status, TMB, histology, immune infiltration and other clinically validated features.

For a broader discussion of checkpoint resistance, see: Immunotherapy Resistance: Why PD-1/PD-L1 Stops Working .

10. How the TME Contributes to Cancer Treatment Resistance

Treatment resistance is often described as though the cancer cell simply mutates around the treatment. That is only part of the story.

Resistance can arise through tumor-cell genetics, altered signaling, epigenetic adaptation, immune escape, pharmacologic factors and changes in the microenvironment.

Resistance Mechanism	TME Contributor	What May Be Happening
Physical resistance	Dense ECM, fibrosis, high interstitial pressure	Therapy may have difficulty reaching all tumor regions uniformly.
Vascular resistance	Abnormal tumor vessels	Perfusion and delivery of oxygen, drugs and immune cells may be uneven.
Hypoxic resistance	Low-oxygen niches	HIF-related adaptation can alter survival, metabolism and treatment sensitivity.
Metabolic resistance	Glucose competition, lactate, adenosine, amino-acid metabolism	Tumor and immune cells can adapt to resource constraints and metabolic stress.
Immune resistance	Tregs, MDSCs, TAMs, CAFs and suppressive metabolites	Immune cells may be excluded, exhausted or functionally suppressed.
Bypass signaling	Growth factors and stromal signaling	Alternative pathways may support survival after a dominant pathway is blocked.
Ecosystem remodeling	Treatment-driven changes in immune and stromal populations	The post-treatment ecosystem may differ biologically from the pretreatment tumor.

This is why resistance can be dynamic. The biology of a tumor at diagnosis may differ from the biology of the same disease after chemotherapy, targeted therapy, radiation or immunotherapy.

A particularly important consequence is that the same resistance phenotype can have different causes in different cancers.

Explore the broader: Cancer Treatment Resistance Atlas .

11. TME Biomarkers and How the Microenvironment Is Studied

No single laboratory test captures the entire tumor microenvironment. Different technologies answer different questions.

Method	What It Can Examine	Main Limitation
Routine histology	Tissue architecture, morphology, fibrosis and general cellular patterns	Limited molecular and cellular resolution.
IHC	Selected proteins such as PD-L1 and immune/stromal markers	Usually evaluates a limited number of markers at a time.
Multiplex IHC / IF	Multiple cell populations and markers while preserving tissue context	Requires specialized technical and analytical validation.
Flow cytometry	Detailed immune-cell phenotypes	Much of the original tissue architecture is lost.
Bulk RNA sequencing	Gene-expression patterns across a tissue sample	Signals from multiple cellular populations are averaged together.
Single-cell sequencing	Cellular populations and molecular states at single-cell resolution	Expensive, complex and often separated from spatial information.
Spatial transcriptomics	Gene expression mapped to tissue location	Still developing for routine clinical use.
Digital pathology	Cell density, location and tissue architecture	Requires validated algorithms, image quality and standardized interpretation.

Common TME-related markers and signals

Marker / Feature	Biological Context	Interpretation
PD-L1	Immune checkpoint signaling	Clinically relevant in selected cancers and indications; meaning depends on assay and clinical setting.
CD8	Cytotoxic T-cell infiltration	Provides information about immune infiltration, but quantity alone does not prove function.
FOXP3	Regulatory T-cell biology	Can help characterize regulatory immune populations.
CD68 / CD163	Macrophage populations	Can identify macrophage-rich environments but does not fully define macrophage function.
FAP	Fibroblast biology	Used in research to characterize activated fibroblast subsets.
α-SMA	Activated stromal / myofibroblast phenotype	Can contribute to stromal characterization.
HIF-1α	Hypoxia signaling	Research marker for hypoxia-associated biology; interpretation is context dependent.

12. Can the Tumor Microenvironment Be Targeted?

Yes—but the key distinction is between established therapies that affect the TME as part of their action and experimental approaches specifically designed to manipulate the TME.

Strategy	Biological Objective	Evidence Position
Immune checkpoint blockade	Restore anti-tumor immune activity through defined checkpoint pathways	Established in multiple cancer types and clinical settings, but response is not universal.
Anti-angiogenic therapy	Alter abnormal tumor vasculature and signaling	Established in selected indications; TME effects are part of broader treatment biology.
CAF / stromal targeting	Alter fibroblast-mediated signaling or extracellular matrix	Active research; clinical results vary and stromal heterogeneity is a major challenge.
Myeloid targeting	Modify MDSC or macrophage-mediated immune suppression	Active clinical and translational research.
Adenosine-pathway targeting	Reduce metabolically mediated immune suppression	Investigational.
Lactate / MCT targeting	Modify lactate transport or signaling	Predominantly preclinical or early translational research.
Hypoxia-directed approaches	Alter or exploit hypoxic tumor regions	Active research with context-dependent clinical development.
TME normalization	Improve stromal, vascular and immune conditions rather than simply destroying tissue	Important translational concept; implementation depends on the specific intervention.

The central idea is increasingly described as microenvironmental reprogramming: changing the conditions around cancer cells so that immune attack or conventional therapy may become more effective.

13. Repurposed Drugs and Supplements: What the Evidence Actually Shows

The TME has also become a major area for drug-repurposing research. This includes conventional drugs, antiparasitic medicines and selected nutritional compounds that have been investigated for effects on fibrosis, metabolism, immune signaling, hypoxia or tumor-cell pathways.

However, biological plausibility is not the same as clinical efficacy. The most useful approach is to separate mechanism, preclinical evidence, early human studies and established treatment.

Losartan and stromal modulation

Losartan is an angiotensin II receptor blocker used for cardiovascular indications. It attracted oncology interest because renin-angiotensin signaling can influence fibrosis, extracellular-matrix formation and vascular biology.

An earlier single-arm phase 2 study evaluated FOLFIRINOX plus losartan followed by chemoradiotherapy in locally advanced pancreatic cancer and reported an encouraging resection rate and survival signal. However, because that study was not randomized, the outcomes could not establish that losartan itself caused the result.

The later randomized AFPAC analysis compared mFOLFIRINOX with mFOLFIRINOX plus losartan in 88 patients. Median overall survival was 10.4 months versus 9.1 months, with a hazard ratio of 0.76 and p = 0.392. The difference was not statistically significant.

Evidence position: losartan is an important example of TME/stromal research, but current evidence does not establish it as a proven pancreatic-cancer TME therapy.

AFPAC randomized clinical trial — PubMed

Vitamin D receptor and stromal reprogramming

Pancreatic stellate cells and other stromal populations can express the vitamin D receptor (VDR). Experimental work has shown that VDR activation can push activated stellate cells toward a more quiescent phenotype and alter the stromal environment.

A landmark 2014 study using the VDR ligand calcipotriol demonstrated stromal remodeling and improved chemotherapy delivery in experimental pancreatic cancer models.

This is an important biological finding, but it should not be misinterpreted as evidence that taking high-dose vitamin D treats pancreatic cancer. The biological pathway and the supplement are not interchangeable concepts.

Sherman et al. Vitamin D receptor-mediated stromal reprogramming — PubMed

Metformin and metabolic remodeling

Metformin is frequently discussed in metabolic oncology because of its effects on glucose metabolism and insulin-related signaling. It is also attractive as a repurposing candidate because it has a well-established clinical history.

The problem is that biological rationale has not translated into consistent anticancer efficacy. A meta-analysis of randomized trials found no statistically significant overall improvement in progression-free or overall survival from metformin across the cancer populations studied.

Evidence position: metformin remains an area of research rather than a general-purpose anticancer therapy.

Meta-analysis of randomized trials of metformin in cancer

Ivermectin

Ivermectin has generated substantial preclinical interest. Laboratory studies have reported effects on cancer-cell proliferation, apoptosis and signaling pathways, while some experimental work has investigated immune modulation and the possibility of converting immunologically "cold" tumors into more inflamed states.

These findings are scientifically interesting, but human clinical evidence remains limited. A 2025 review concluded that there were no large randomized trials establishing therapeutic cancer benefit.

ASCO issued a June 2026 Clinical Notice cautioning that ivermectin and fenbendazole should not be used to treat cancer, including as adjuncts to established therapy, outside the safeguards of a well-designed clinical trial.

Evidence position: predominantly preclinical for oncology efficacy, with limited human clinical evidence.

Ivermectin in Cancer Treatment — PubMed  |  ASCO Clinical Notice, June 2026

Mebendazole and fenbendazole

Mebendazole and fenbendazole are benzimidazole antiparasitic drugs that have attracted cancer research interest because of laboratory findings involving microtubules, signaling and metabolism.

Mebendazole has considerably more human medical-use history than fenbendazole, and early oncology studies continue to investigate whether particular combinations or cancer subtypes might justify further research.

A 2025 phase 1 study evaluated mebendazole in children with refractory or recurrent brain tumors. Such studies help answer questions about feasibility and safety, but a phase 1 study is not proof of anticancer efficacy.

Fenbendazole requires even greater caution. It is a veterinary medication and is not approved for human use. Preclinical findings and anecdotal reports cannot establish benefit in humans.

Evidence position: investigational, with substantially stronger mechanistic and preclinical evidence than high-quality randomized clinical evidence.

Phase 1 mebendazole study in pediatric brain tumors — PubMed

Safety distinction: an approved drug's safety profile for its original indication does not establish safety, dose, drug interactions or efficacy for cancer. Fenbendazole is a veterinary medication and should not be presented as an established human cancer treatment.

For the broader evidence and safety review of ivermectin, mebendazole, fenbendazole, niclosamide and atovaquone, see: Repurposed Drugs for Cancer: Evidence-Based Review .

Supplements and nutraceuticals

Compounds such as curcumin, EGCG, sulforaphane, omega-3 fatty acids, quercetin and vitamin D have been investigated for inflammatory signaling, oxidative stress, fibrosis, metabolism or immune pathways.

The evidence is highly uneven, and in many cases remains predominantly preclinical.

Compound	Main Research Interest	Evidence Position
Curcumin	Inflammatory signaling, NF-κB, STAT3, fibrosis and cell signaling	Predominantly preclinical.
EGCG	Signaling, angiogenesis and extracellular-environment effects	Predominantly preclinical.
Sulforaphane	Redox biology, epigenetic signaling and cellular defense pathways	Early translational research.
Omega-3 fatty acids	Inflammatory and immune pathways	Mixed clinical evidence; anticancer treatment claims remain unproven.
Quercetin	Inflammation, oxidative stress and cellular signaling	Predominantly preclinical.
Vitamin D / VDR biology	Stromal and immune signaling, especially in pancreatic cancer research	Mechanistic and clinical research; supplementation is not established cancer therapy.

14. The TME in a Systems-Oncology Framework

One of the most useful ways to think about the TME is to stop viewing it as a separate topic. It is one layer of a larger biological system.

Tumor genotype → signaling → phenotype → metabolism → microenvironment → immune response → treatment pressure → adaptation → resistance

Consider a simplified example:

A tumor acquires a signaling alteration that increases proliferation. Greater proliferation increases nutrient demand. Increased glycolysis produces more lactate. Hypoxia develops as tumor growth exceeds vascular supply. CAFs remodel the extracellular matrix. Abnormal vessels worsen perfusion. Immune cells struggle to enter the tumor. Treatment eliminates sensitive cancer-cell populations while resistant populations survive in particular spatial niches.

No single step completely explains the resulting resistance. The biology is interconnected.

Systems-oncology question:
Rather than asking only "Which mutation does this cancer have?", a more complete question is:

What combination of tumor-cell biology, immune state, stromal architecture, vascular function and metabolic conditions is sustaining this cancer right now?

15. What Does TME Analysis Mean for a Patient?

TME analysis can sound more clinically mature than it actually is. Some TME-related information is already incorporated into routine cancer care, while much more advanced profiling remains primarily research-oriented.

Depending on the cancer, clinicians may consider:

PD-L1 MSI / MMR TMB Histology Immune infiltration Stromal features Molecular alterations Prior treatment response

More advanced research can include multiplex imaging, single-cell sequencing, spatial transcriptomics, spatial proteomics and integrated multi-omic analysis.

Why biopsy timing matters

A biopsy is a snapshot of one location at one point in time. Tumors can be spatially heterogeneous, and treatment itself can change the composition of the TME.

Consequently, when cancer progresses after treatment, clinicians may sometimes consider whether new tissue, liquid biopsy, imaging or other molecular information could change the understanding of the disease.

This does not mean every patient needs repeat biopsy or advanced TME profiling. The usefulness of additional testing depends on the cancer type, treatment setting and whether the result could actually influence management.

16. TME and the Cancer Treatment Resistance Atlas

The TME can be incorporated directly into a resistance framework:

Resistance Phenotype	TME Contributor	Potential Signal	Research Direction
Immune exclusion	CAFs, ECM, abnormal endothelium	TGF-β, CXCL12, matrix remodeling	Stromal and vascular modulation
Immune suppression	Tregs, MDSCs, TAMs	IL-10, TGF-β, arginase-related pathways, checkpoints	Myeloid and immune reprogramming
Metabolic suppression	Tumor and stromal cells	Lactate, adenosine, glucose competition, kynurenine	Metabolic-immunologic combinations
Hypoxia	Abnormal vessels and high metabolic demand	HIF signaling, VEGF and hypoxia-associated metabolism	Hypoxia-directed and vascular approaches
Poor drug penetration	Dense ECM, interstitial pressure, abnormal perfusion	Collagen-rich matrix, vascular dysfunction	Drug-delivery and stromal-remodeling strategies
Alternative growth signaling	Stromal and immune-derived factors	HGF, FGF, EGF and cytokine signaling	Combination targeted strategies
Post-treatment remodeling	Changes in immune and stromal populations	Altered cellular composition and spatial niches	Longitudinal and spatial profiling

This framework connects naturally with the broader Cancer Advisor resistance model:

Cancer Type → Biomarker → Treatment → Response → Resistance → Mechanism → Resistance Biomarker → Testing → Next Strategy

Read the Cancer Treatment Resistance Atlas

17. Where TME Research Is Going

The next stage of TME research is moving from simply counting cells toward understanding spatial relationships, cell states and dynamic change over time.

Researchers increasingly want to know:

Which cells are present? Where are they located? Which cells communicate with each other? Which regions are hypoxic? Where are immune cells excluded? Which spatial niches contain resistant cancer cells? How does the ecosystem change after therapy?

Traditional bulk sequencing averages together many populations. Single-cell and spatial technologies attempt to restore the context that bulk measurements lose.

The long-term objective is an integrated tumor ecosystem map combining:

Genomics + transcriptomics + proteomics + immune profiling + spatial biology + metabolism + imaging + treatment history

Such an approach may eventually allow oncology to identify not only the mutation driving a tumor, but also the local ecosystem that allows resistant cells to survive.

18. Tumor Microenvironment: Key Takeaways

1. The TME is the ecosystem surrounding a tumor, including immune cells, fibroblasts, blood vessels, extracellular matrix, metabolites and signaling molecules.
2. The relationship is bidirectional: tumors reshape their environment, while the environment reshapes tumor behavior.
3. CAFs and extracellular matrix can contribute to immune exclusion, tissue stiffness, abnormal signaling and treatment resistance.
4. Desmoplasia is especially important in pancreatic cancer, but stromal remodeling occurs across many cancers.
5. Abnormal tumor vasculature can contribute to hypoxia, uneven drug delivery and impaired immune-cell trafficking.
6. Hypoxia is a signaling state that connects metabolism, angiogenesis, immune biology and resistance.
7. Lactate, adenosine, glucose competition and amino-acid metabolism can influence the immune environment.
8. "Hot" and "cold" are useful concepts, but immune-desert and immune-excluded tumors illustrate why a binary classification is incomplete.
9. PD-L1, TMB and MSI/MMR remain important in selected clinical settings, but none describes the entire TME.
10. The TME may contribute to physical, vascular, hypoxic, metabolic and immune forms of treatment resistance.
11. Modern TME research increasingly emphasizes normalization and reprogramming rather than indiscriminate destruction of stroma.
12. Repurposed drugs and supplements remain a heterogeneous research field; promising mechanisms do not automatically establish clinical benefit.
13. Spatial and single-cell technologies are expanding the ability to study tumor ecosystems in context.
14. The most useful resistance question is often not simply "What mutation is present?" but "What biological system is sustaining the cancer now?"

19. Frequently Asked Questions

What is the tumor microenvironment in simple terms?

It is the biological environment around a cancer cell. It includes immune cells, fibroblasts, blood vessels, extracellular matrix, metabolites, nutrients, signaling molecules and physical conditions such as hypoxia.

Why is the tumor microenvironment important?

The TME can influence tumor growth, immune recognition, metastasis, drug delivery and treatment resistance. Tumors can also remodel their environment as they grow.

What are cancer-associated fibroblasts?

CAFs are stromal cells associated with tumors that can remodel extracellular matrix and influence immune-cell behavior, signaling, angiogenesis and tissue structure. CAF populations are heterogeneous, and not every fibroblast has the same biological effect.

What is a hot tumor?

A "hot" tumor generally refers to an immune-inflamed tumor with substantial immune-cell infiltration and evidence of an existing immune response. It is a conceptual biological classification, not a universal clinical diagnosis.

What is a cold tumor?

A cold or immune-desert tumor generally has limited effective immune infiltration. This can reduce the biological foothold available for checkpoint-based immune activation.

What is an immune-excluded tumor?

An immune-excluded tumor contains immune cells around or near the tumor but has limited penetration into tumor nests. Stromal architecture, chemokine signaling and abnormal blood vessels can contribute to this phenotype.

Does hypoxia make cancer harder to treat?

Hypoxia can contribute to treatment resistance through changes in signaling, metabolism, angiogenesis and immune function. Its importance varies by tumor type and treatment.

Does lactate help cancer cells?

Lactate can influence tumor metabolism and the surrounding immune environment. High lactate has been associated with impaired function of some immune effector cells, although lactate biology is complex and highly context dependent.

Can the tumor microenvironment be tested?

Yes. Depending on the setting, testing can include pathology, IHC, multiplex imaging, flow cytometry, RNA profiling, single-cell sequencing and spatial transcriptomics. Not all approaches are routinely available or clinically validated for treatment selection.

Can doctors treat the tumor microenvironment?

Some established cancer therapies affect components of the TME, including checkpoint inhibitors and anti-angiogenic therapies. Many other approaches targeting CAFs, MDSCs, adenosine, lactate or specific stromal pathways remain investigational.

Does a favorable TME guarantee that immunotherapy will work?

No. Treatment response depends on multiple interacting factors. A favorable immune environment may improve the biological conditions for response but cannot guarantee an individual outcome.

Can a cold tumor become hot?

Some experimental and clinical strategies are designed to increase immune infiltration or activation, including selected combinations of radiation, chemotherapy, immunotherapy and other approaches. Whether such a strategy is appropriate depends on the cancer type and clinical evidence.

Is the "desmoplastic shield" the same as the tumor microenvironment?

No. The desmoplastic shield is a useful description of dense fibroinflammatory stroma in tumors with prominent desmoplasia. The TME is much broader and includes immune cells, vasculature, metabolites, extracellular matrix and physical conditions.

Is losartan proven to treat pancreatic cancer by remodeling the TME?

No. Early non-randomized data generated interest, but the later randomized AFPAC analysis did not show a statistically significant overall-survival benefit from adding losartan to mFOLFIRINOX.

Are ivermectin or fenbendazole established TME treatments?

No. Both have generated substantial laboratory research interest, but current evidence does not establish them as proven cancer or TME treatments. ASCO specifically cautioned against use of ivermectin and fenbendazole for cancer outside a well-designed clinical trial.

Why can two metastases from the same cancer behave differently?

Different organs and different lesions can develop distinct immune, vascular, stromal and metabolic environments. Spatial and organ-specific differences can therefore contribute to different responses to treatment.

Editor’s Note

The tumor microenvironment is one of the most useful concepts for connecting several fields of modern oncology that are often discussed separately: tumor genetics, immunotherapy, cancer metabolism, angiogenesis, stromal biology, drug delivery, spatial biology and treatment resistance.

The important shift is not from "treating the cancer" to "treating the microenvironment." It is toward understanding the tumor as an interacting system.

That system can include malignant-cell genetics, immune recognition, stromal architecture, blood supply, metabolism and evolutionary pressure from treatment. A treatment may eliminate one population while leaving another population better adapted to the new environment.

The practical implication is that TME research is most useful when connected to: cancer type → biomarkers → treatment history → resistance mechanism → testing → evidence-supported next strategy.

Medical disclaimer: This article is for educational and informational purposes only. It does not provide individualized medical advice, diagnosis or treatment. Cancer treatment decisions should be made with appropriately qualified healthcare professionals using the patient's diagnosis, pathology, biomarkers, imaging, treatment history, medications and overall clinical circumstances. Experimental, repurposed or off-label therapies should not be substituted for established cancer care without appropriate medical supervision.

20. References and Further Reading

1. National Cancer Institute. Tumor Microenvironment. NCI
2. Kung HC, Zheng KW, Zimmerman JW, et al. The tumour microenvironment in pancreatic cancer — new clinical challenges, but more opportunities. Nature Reviews Clinical Oncology. 2025;22:969–995. Nature
3. Wu B, Zhang B, Li B, et al. Cold and hot tumors: from molecular mechanisms to targeted therapy. Signal Transduction and Targeted Therapy. 2024;9:274. DOI | PubMed
4. Ramaswamy A, Bhargava P, Gota V, et al. Efficacy of losartan plus modified FOLFIRINOX versus modified FOLFIRINOX in advanced pancreatic cancers: A randomized clinical trial (AFPAC Study). Cancer. 2025. PubMed
5. Sherman MH, et al. Vitamin D receptor-mediated stromal reprogramming suppresses pancreatitis and enhances pancreatic cancer therapy. Cell. 2014. PubMed
6. Aliabadi A, Moradi SZ, Abdian S, et al. Critical dysregulated signaling pathways in drug resistance: highlighting the repositioning of mebendazole for cancer therapy. Frontiers in Pharmacology. 2025. PubMed
7. Phan P, Stapleton SL, Riggins GJ, et al. Phase 1 study of mebendazole therapy for refractory/progressive or recurrent pediatric brain tumors. Neuro-Oncology Practice. 2025. PubMed
8. Ivermectin in Cancer Treatment: Should Healthcare Providers Caution or Explore Its Therapeutic Potential? 2025 review. PubMed
9. Efficacy of metformin therapy in patients with cancer: a meta-analysis of 22 randomised controlled trials. BMC Medicine. BMC Medicine
10. American Society of Clinical Oncology. Oncologists Urged to Take Proactive Approach When Discussing Ivermectin, Fenbendazole. June 17, 2026. ASCO

Continue Your Research

Cancer Treatment Resistance Atlas  |  Immunotherapy Resistance  |  Metabolic Oncology  |  Smart Cancer Resources & Research Guide

Cancer Advisor is an independent oncology information platform. Experimental research is presented for transparency and research navigation and should not be confused with established cancer treatment.