Drug Resistance in Breast Cancer Liver Metastases: Understanding Why Treatments Stop Working and What It Means for Patients

Table of Contents

• Key Points
• Introduction: Why Breast Cancer Liver Metastases Are So Difficult to Treat
• Factors Contributing to Drug Resistance in BCLM
• The Liver's Unique Immune Microenvironment
• The Tumor's Support Structure: Cancer-Associated Fibroblasts and the Extracellular Matrix
• Metabolic Reprogramming: How Cancer Cells Change Their Fuel Source
• Extracellular Vesicles: Cellular Messengers of Resistance
• Clinical Implications: What This Means for Treatment
• Limitations of Current Research
• Recommendations for Patients
• Frequently Asked Questions
• Source Information

Key Points

• BCLM incidence is 40–50%, with a death rate of 50–62%; average overall survival is 31 months.
• The liver's natural immune tolerance helps cancer cells evade attack, reducing immunotherapy effectiveness.
• Combination therapies targeting multiple resistance mechanisms show promise in preclinical models.
• A fasting-mimicking diet may enhance fulvestrant's effect in BCLM, but is preliminary—consult your care team.
• Many drug targets (CXCR4, STAT3, PI3K, etc.) have ongoing clinical trials, offering potential options.

Introduction: Why Breast Cancer Liver Metastases Are So Difficult to Treat

Breast cancer is the leading cause of cancer-related death in females worldwide. When breast cancer spreads, it most often travels through the bloodstream to the bones, lungs, liver, and brain. Of these, the liver is one of the most common sites for solid metastases. For patients, a liver metastasis diagnosis carries heavy weight: the clinical incidence of breast cancer liver metastases is 40%–50%, and the death rate ranges from 50%–62%.

Patients with BCLM face limited treatment options, and drug resistance is highly prevalent — meaning that even when treatments work initially, cancer cells often find ways to escape them. The average overall survival (OS) for BCLM patients receiving treatment is just 31.0 months.

To understand why this happens, researchers have gone back to a theory first proposed in 1889 by Stephen Paget. He called it the "seed and soil" hypothesis — comparing cancer cells to "seeds" and the organs they spread to as "soil." Paget suggested that distant tumor metastases can only occur if the seeds (circulating tumor cells) are compatible with the soil (the organ they arrive at). Today, this model still guides scientific thinking about BCLM.

The development of BCLM is a complex journey. Breast cancer cells must invade blood vessels (a process called intravasation), survive in circulation, arrest at the liver site by adhering to sinusoidal endothelial cells (margination), migrate through those cells into the liver tissue (extravasation), and then proliferate to form metastatic colonies. Along the way, inflammatory factors, chemokines, and cell adhesion molecules all play supporting roles in helping cancer cells establish themselves in the liver.

Drug resistance itself comes in two forms. Primary resistance refers to cancers that never respond to initial treatment at all. Acquired resistance develops after prolonged treatment in tumors that originally responded to therapy. The "key determinants" of tumor resistance include tumor burden and growth kinetics, tumor heterogeneity, physical barriers at the cell membrane, the immune system and microenvironment, undruggable cancer drivers, and the impact of drug pressure itself.

Factors Contributing to Drug Resistance in BCLM

Understanding the mechanisms of drug resistance in BCLM is crucial for developing better treatment strategies. This review identifies several major contributors: the unique immune environment of the liver, the tumor stroma (supporting tissue), metabolic reprogramming of cancer cells, and extracellular vesicles — tiny membrane-wrapped packages released by cells that carry messages between them.

The Liver's Unique Immune Microenvironment

The liver is not just a passive destination for cancer cells — it has its own complex ecosystem that shapes how tumors behave. The tumor-immune microenvironment consists of immune cells, cytokines (cell-signaling proteins), cancer cells, and the extracellular matrix (ECM), the supportive scaffolding that holds tissues together. All of these components play critical roles in both the progression of liver tumors and their resistance to drugs.

Immunoreactive Cells: A Crowded Neighborhood with a Problem

As an immune organ, the liver is packed with immunoreactive cells, including Kupffer cells (specialized immune cells unique to the liver), hepatic sinusoidal endothelial cells, hepatic stellate cells (HSCs), pit cells, natural killer T cells, gamma-delta T cells, and dendritic cells. The liver also produces immune-related molecules such as C-reactive protein and soluble pattern-recognition receptors, which are central to systemic inflammation and immunity.

Here is the paradox: although the liver is full of immune cells, it maintains a unique immunotolerant microenvironment. This tolerance is partly due to the liver's embryonic origin as a blood-forming organ, the flow of portal blood from the gastrointestinal tract and spleen, and mucosal immunity from the biliary system. Unlike normal capillary endothelial cells, hepatic sinusoidal endothelial cells do not have a basement membrane, which facilitates direct exchange between hepatocytes (liver cells) and blood — and allows lymphocytes to come into direct contact with liver cells.

Because the liver is constantly exposed to bacterial components and dietary antigens flowing from the gastrointestinal tract through the portal vein, it must maintain a level of tolerance. This balances the elimination of harmful bacteria with avoiding excessive inflammation from harmless intestinal contents. But this tolerance creates an unintended consequence: the liver becomes a safe haven where cancer cells can avoid immune attack.

Checkpoint Inhibitors and the Liver's Immune Desert

The clinical impact of this immunotolerant environment is significant. Experiments in mice have shown that resistance of liver tumors to anti-PD-L1 antibody therapy (a type of immunotherapy) was largely due to the liver's unique immunotolerant microenvironment, independent of the tumor's origin or type. PD-L1 (programmed death-ligand 1) is a protein that cancer cells use to switch off immune attacks; drugs that block PD-L1 aim to restore the immune system's ability to fight cancer.

In even more striking findings, Yu and colleagues demonstrated that liver metastases actually "siphon off" activated CD8+ T cells — the immune system's cancer-killing cells — from the bloodstream. As a result of their interaction with FasL+CD11b+F4/80+ monocyte-derived macrophages, these activated antigen-specific Fas+CD8+ T cells undergo apoptosis (programmed cell death) inside the liver. In plain terms: the liver metastasis acts like a trap, drawing in the immune cells that should be fighting the cancer and killing them. In preclinical models, this creates what researchers call a systemic immune desert — the entire body's immune response is suppressed, not just the area around the tumor.

Liver metastases also exploit host peripheral tolerance mechanisms to cause acquired immunotherapy resistance, meaning that even patients whose cancer initially responded to immunotherapy can lose that response over time.

Lessons from Liver Cancer: Immunotherapy Progress and Caution

Despite the poor results of immunotherapy for liver metastases, targeted PD-1 monoclonal antibody treatment has shown some promise in treating primary hepatocellular carcinoma (HCC), a type of cancer that starts in the liver itself. In May 2020, the US Food and Drug Administration (FDA) approved the combination of Tecentriq (atezolizumab), which targets PD-L1, combined with Avastin (bevacizumab) for clinical use in HCC. Several other drugs — cabozantinib, Keytruda (pembrolizumab), nivolumab, and nivolumab combined with ipilimumab — are currently approved as second-line treatments for HCC.

Hu and colleagues revealed that combining interferon-alpha with anti-PD-1-based immunotherapy shows promising anticancer effects in HCC patients. Their proposed mechanism involves the combination therapy remodeling the tumor-immune microenvironment by inducing CD27+CD8+ T cell infiltration, which then causes HCC tumor regression.

Combination immunotherapy has shown potential in a variety of tumors. Currently, the combination of PD-1 antibody and cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) antibody has been approved for treating some cancers. For example, nivolumab combined with ipilimumab has been approved for melanoma, non-small cell lung cancer, HCC, and renal cell carcinoma. This approach may also become a promising new direction for BCLM treatment.

However, there are important cautions. Patients receiving immune combination therapy may experience higher rates of grade 3–4 toxicity (severe side effects), and several immune combination therapy clinical trials have actually been discontinued for this reason. Given the liver's special role in drug metabolism, the potential for significant immune-related toxicity must be carefully weighed when exploring this approach in BCLM.

VEGF: Blood Vessel Growth and Immune Suppression Combined

Vascular endothelial growth factor (VEGF) is the most established biological mediator of tumor angiogenesis — formation of new blood vessels that feed tumors. It is a cytokine induced by local tissue hypoxia (low oxygen) and acidosis (excess acid), and it promotes the growth of defective, leaky tumor blood vessels. Critically, VEGF also has direct local and systemic immunosuppressive effects beyond its effects on blood vessels, because it blocks immune effector cells from infiltrating tumors.

Anti-VEGF therapy reverses these immune suppressive effects. It is associated with increased infiltration of regulatory cells, myeloid-derived suppressor cells, and M2-type tumor-associated macrophages (TAMs) into tumors. Researchers have found that blocking VEGF reduced the number of PD-L1+ and TIM3+ infiltrating T lymphocytes in a mouse model of colorectal cancer liver metastasis. The key finding: mice injected with colon cancer cells did not show a significant anti-tumor effect when PD-L1 alone was blocked, but they did show a significant reduction in tumor burden when the treatment was combined with VEGF inhibitors.

This suggests that liver tumors that produce VEGF-A may benefit from combining anti-angiogenic (blood-vessel-blocking) molecules with immunomodulators that target inhibitory checkpoints. In addition, non-coding ribonucleic acids such as microRNA-934 (miRNA-934) can induce differentiation of tumor-associated macrophages to the M2 phenotype (a pro-tumor, pro-healing type of immune cell), thereby promoting tumor progression, metastasis, and therapeutic resistance.

GRP78: A Stress Protein with a Dark Side

Glucose-regulated protein 78 (GRP78) belongs to a group of highly conserved heat shock proteins — proteins that cells produce in response to stress. It has important stress-response functions and is involved in the unfolded protein response (UPR) and endoplasmic reticulum stress responses, as well as cellular metabolism, hypoglycemia (low blood sugar), hypoxia (low oxygen), acidosis, viral infection, and DNA damage repair.

Studies have shown that overexpression of cell-surface GRP78 (CS-GRP78) in laboratory experiments promotes the invasiveness of breast cancer tumor cells and enhances their ability to colonize and proliferate in the liver. GRP78 expression is associated with cancer cell invasion and drug resistance. The UPR signaling network is activated in cancer cells by endoplasmic reticulum stress pathways, and GRP78 increases tumor chemoresistance by regulating the UPR. GRP78 also reduces insulin-like growth factor binding protein 3 entry into cells, which promotes breast cancer tumor progression.

Tseng and colleagues made an especially important discovery: the C-terminal domain of CS-GRP78 can cause tamoxifen resistance in breast cancer through activation of STAT3 (signal transducer and activator of transcription 3). Tamoxifen is a cornerstone endocrine therapy for hormone-receptor-positive breast cancer, so this finding has direct relevance for many patients. The evidence suggests that GRP78 may be responsible for the development of drug resistance in BCLM — although the exact mechanism of how it influences immune cells in the tumor microenvironment remains to be fully clarified.

The Tumor's Support Structure: Cancer-Associated Fibroblasts and the Extracellular Matrix

Beyond immune cells, the tumor stroma — the non-cancerous supporting tissue within and around a tumor — is an important component of the liver metastasis microenvironment. Cancer-associated fibroblasts (CAFs) are the most abundant cells in the tumor microenvironment and are a key source of the extracellular matrix (ECM), which constitutes what doctors call the desmoplastic stroma (a dense, fibrous connective tissue that forms around tumors).

CAFs regulate cancer occurrence, progression, metastasis, and resistance to therapy by remodeling the tumor stroma and through paracrine actions (cell-to-cell communication via secreted signals). The CAFs found in stroma-rich liver metastases mainly originate from hepatic stellate cells (HSCs). It has been demonstrated that CAFs and activated HSCs confer both chemoresistance and radio-resistance to liver metastases.

Mechanistically, CAF-secreted exosomes significantly increase levels of miR-92a-3p in tumor cells, thereby activating the Wnt/beta-catenin pathway and directly inhibiting F box and WD repeat domain containing 7 and modulator of apoptosis 1. The end result: mitochondria-associated apoptosis is inhibited, promoting tumor progression and chemoresistance.

Cancer Stem Cells: The Seeds Within the Seeds

Cancer stem cells (CSCs) — a small population of cells within tumors that can self-renew and drive tumor growth — also play a key role in drug resistance. A study in mouse models found that the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) promotes the release of the nuclear cytokine interleukin-33 (IL-33) from CSCs. This promotes the differentiation of macrophages with a high affinity for the immunoglobulin E receptor FcεRIa. These specialized macrophages then send paracrine transforming growth factor beta (TGF-beta) signals to the cancer stem cells, leading to tumor progression and drug resistance.

Additionally, abnormal activation of the PI3K/PKB (phosphatidylinositide 3-kinase/protein kinase B) signaling pathway in CSCs leads to upregulation of ATP-binding cassette (ABC) transporter protein expression. These transporter proteins actively pump chemotherapeutic drugs out of cancer cells — a bit like cellular bouncers ejecting unwanted guests — which directly leads to drug resistance.

The Extracellular Matrix: A Physical and Chemical Barrier

The abnormal composition and structure of the ECM in solid tumors can make anticancer drugs ineffective. Among ECM proteins, collagen is the most abundant structural protein in the liver. Disproportionate collagen concentrations can cause an altered cell phenotype and a distorted structure with abnormal blood flow in the liver. High collagen content is a key barrier to drug penetration through the ECM-associated interstitial proteins, leading to poor drug distribution and reduced efficacy of chemotherapeutic agents.

The stiffness of the ECM also matters. By activating multiple mechanotransduction pathways (pathways that convert physical forces into cellular responses), ECM stiffness influences tumor metastasis, growth, and drug resistance. In breast cancer, ECM rigidity promotes epithelial-mesenchymal transition (EMT) — a process where cancer cells become more mobile and invasive — and metastasis via the twist family BHLH transcription factor 1-Ras-GTPase activating protein SH3 domain-binding protein 2 pathway. ECM rigidity also promotes the expression of angiogenesis-related factors such as VEGF-A, hypoxia-inducible factor-1 alpha, and TGF-beta 1.

A recent study showed that an ECM-derived mechanical signal can upregulate expression of NEAT1 (nuclear-enriched abundant transcript 1), a long non-coding RNA. NEAT1 can promote sorafenib resistance (sorafenib is a targeted therapy used in liver cancer) by enhancing autophagy-related protein 3 expression and autophagy — a process where cells recycle their own components, which cancer cells use to survive treatment stress.

Chemotherapy and radiotherapy can also disrupt the tumor microenvironment and induce production of senescence-associated secretory phenotypes (SASPs). Stromal cells in the tumor microenvironment can rapidly enter the aging (senescence) stage during chemotherapy, producing and releasing large amounts of SASP factors. Among them, serine protease inhibitor Kazal type 1 can activate cancer cells that survived treatment and make them resistant to the drug.

Metabolic Reprogramming: How Cancer Cells Change Their Fuel Source

Cancer cells exhibit remarkable metabolic plasticity — the ability to change how they produce energy depending on their environment. When distant metastasis occurs, they adapt to the new metastatic environment by rewiring their metabolic pathways. Understanding this reprogramming is essential because it directly contributes to drug resistance.

Energy Metabolism and the Warburg Effect

In normal mammalian cells, glycolysis (breaking down glucose for energy) is inhibited under aerobic conditions. But in the 1920s, Otto Warburg discovered that liver cancer cells have more active glycolytic activity than normal hepatocytes, and that malignant tumor cells remain actively glycolytic even when oxygen is plentiful. This metabolic feature, called aerobic glycolysis, is now known as the Warburg effect.

The Warburg effect is characterized by high glucose uptake, active glycolysis, and high lactic acid content in metabolites. It explains a seemingly wasteful phenomenon: tumor cells consume sugar during proliferation without being efficiently productive. Under aerobic conditions, cancer cells switch from aerobic phosphorylation (the efficient energy-production method) to aerobic glycolysis. The more glucose ingested, the more lactic acid is produced.

This mechanism allows tumor cells to adapt to temporary or permanent hypoxic (low-oxygen) conditions and contributes to the production of nucleotides and amino acids. But there is a darker side: the lactic acid produced promotes tumor invasion and contributes to cell migration, angiogenesis, immune escape, and radioresistance.

Interestingly, a recent study in colon cancer liver metastases found that chemotherapy induced a shift from glycolysis toward oxidative phosphorylation via the sirtuin 1/peroxisome proliferator-activated receptor-gamma coactivator-1 alpha axis, which increased cellular resistance to chemotherapy. This shows that cancer cells actively adapt their metabolism to survive treatment.

There is also promising news regarding diet. Zuo and colleagues reported that a fasting-mimicking diet has been demonstrated to block a glucose surge and reduce glycogen accumulation in the liver, so it may improve the therapeutic effect of fulvestrant (a hormonal therapy used to treat hormone-receptor-positive breast cancer) in BCLM patients.

Amino Acid Metabolism and Other Fuel Sources

Beyond carbohydrates, reprogramming of amino acid metabolism plays an irreplaceable role in tumor development and drug resistance. Glutamine metabolism can provide materials for the over-activated glycolysis and oxidative phosphorylation in tumor cells, and can also induce resistance to chemotherapeutic agents by promoting metabolic homeostasis — helping cancer cells maintain a stable internal environment even under stress.

A glutamine-targeted cancer metastasis therapy in mice has shown that metabolic therapy targeting glutamine metabolism can control liver metastatic tumors. Additionally, Wei and colleagues found that sorafenib resistance in HCC is linked to phosphoglycerate dehydrogenase, the first enzyme in the serine synthesis pathway.

These studies reveal that resistance to treatment of liver metastasis can be overcome through inhibition of dynamic metabolic mechanisms, suggesting new therapeutic ideas. The primary challenge for combination immunotherapy will be finding tumor cell-specific metabolic pathways and metabolites as targets for therapy, and determining the balance between tumor suppression and immune cell activity by exploiting differential metabolic plasticity.

Extracellular Vesicles: Cellular Messengers of Resistance

Extracellular vesicles are various membrane-wrapped structures released by cells. They can be divided into four major categories according to their origin and diameter (the original article introduces this classification, though the detailed breakdown continues in the full published review). These tiny packages carry proteins, lipids, and nucleic acids (including microRNAs) between cells, and they are increasingly recognized as important players in how tumors communicate with their environment — including how they spread resistance to other cancer cells.

For example, CAF-secreted exosomes (a type of extracellular vesicle) increase miR-92a-3p levels in tumor cells, activating drug-resistance pathways. Cancer-secreted exosomal miR-4443 promotes liver metastasis of breast cancer by causing microenvironment-induced TIMP2 loss (TIMP2 is a matrix metalloproteinase inhibitor). And as noted earlier, microRNA-934 can induce the M2 phenotype in tumor-associated macrophages. These findings highlight extracellular vesicles as both biomarkers and potential therapeutic targets.

Ongoing Clinical Trials: New Hope on the Horizon

The review catalogs numerous therapeutic targets currently being investigated. This is especially important for patients, because it shows real momentum in the field. Some notable examples from the research summarized in this review include:

• CXCR4 inhibitors: An open-label Phase Ib/II trial (NCT05103917) studying X4P-001 in combination with toripalimab in patients with locally advanced or metastatic triple-negative breast cancer (TNBC), and a Phase 1 study (NCT05465590) evaluating MB1707 in patients with advanced cancer.
• CXCL12/CXCR4 signaling: A hepatic stellate cell-secreted chemokine CXCL12 induces natural killer (NK) cell quiescence through its receptor CXCR4, suppressing NK cell-sustained breast cancer dormancy — meaning the cancer stays "asleep" but can wake up later.
• CTLA-4: A Phase I/II randomized study (NCT05039632) of NBTXR3 activated by radiation in combination with immunotherapy (anti-CTLA-4 and anti-PD-1) for patients with advanced solid malignancies.
• CD47: A Phase 1 open-label, multicenter, dose-escalation study (NCT05076591) evaluating IMM2902 in patients with HER2-expressing advanced solid tumors.
• Myc: A Phase 1/2 open-label study (NCT05497453) of OTX-2002 for patients with hepatocellular carcinoma and other solid tumor types known to be associated with the MYC oncogene.
• EGFR: A Phase I trial (NCT01432119) of cetuximab and erlotinib (EGFR inhibitors) combined with SIR-Spheres (yttrium-90 microspheres) in patients with advanced malignancies and liver metastases.
• TGF-beta: A trial (NCT01401062) of fresolimumab plus radiotherapy in metastatic breast cancer.

Other promising targets highlighted in the review include STAT3 (combined inhibition of JAK2-STAT3 and SMO-GLI1/tGLI1 pathways), IL-6 (the natural compound nobiletin suppresses IL-6-induced ERK-STAT and JNK-c-JUN pathways), PI3K (SOX2-OT promotes TNBC metastasis by activating PI3K/Akt signaling), PKM2 (circular RNA KIF4A promotes liver metastasis by reprogramming glucose metabolism), AKT (dietary alterations modulate the microRNA 29/30 and IGF-1/AKT signaling axis), MMP (exosomal miR-4443), and Notch1.

Clinical Implications: What This Means for Treatment

These research findings carry real implications for patients with breast cancer liver metastases. First, the liver's natural immune tolerance means that immunotherapy alone is often insufficient — the tumor environment can actively destroy or disable the immune cells that immunotherapy is supposed to empower. This explains the poor response to immunotherapy seen in liver metastases and suggests that strategies to reverse the liver's immune tolerance will be essential.

Second, combination approaches appear to be the future. The research strongly supports combining treatments that target different resistance mechanisms simultaneously. For example:

• Combining anti-VEGF (blood-vessel-blocking) therapy with PD-1/PD-L1 checkpoint inhibitors has shown significantly better results than either alone in preclinical models.
• Combining metabolic targeting (e.g., glutamine inhibitors, fasting-mimicking diets) with immunotherapy may overcome resistance by making cancer cells more vulnerable to immune attack.
• Combining PD-1 antibody with CTLA-4 antibody (nivolumab + ipilimumab) has already been approved for several cancers and may hold promise for BCLM.

Third, diet and metabolism may matter. The finding that a fasting-mimicking diet can improve the effectiveness of fulvestrant in BCLM is preliminary but exciting. It suggests that what patients eat — and when — could influence how well their cancer treatment works.

Fourth, the list of actionable drug targets continues to grow. Pathways involving CXCR4, STAT3, IL-6, PI3K, Notch1, and others each represent potential points of attack. Many of these targets already have clinical trials underway, which is a reason for cautious optimism.

Limitations of Current Research

It is important to be honest about what this research cannot yet tell us. Much of the evidence for drug resistance mechanisms comes from mouse models and laboratory experiments, not directly from human patients. Cancer in a mouse is not the same as cancer in a person, and findings that work in the lab do not always translate to clinical benefit.

The exact mechanisms by which GRP78 influences immune cells in the tumor microenvironment remain to be fully clarified, as do the specific pathways by which tumor metabolism affects immune cell function. The review also points out that combination immunotherapy carries risks of grade 3–4 toxicity — severe side effects that can be dangerous and have led to discontinuation of clinical trials. Because the liver is central to drug metabolism, liver damage from treatments is a particular concern.

Additionally, while the "seed and soil" hypothesis has guided research for over a century, cancer metastasis is far more complex than this simple analogy suggests. Many factors — including the genetic makeup of individual tumors, prior treatments, and the patient's overall health — influence whether these findings will apply to any particular person's cancer.

Finally, the original article is a review of existing research rather than a single experimental study. This means it synthesizes findings from many different research groups, each with different methodologies, models, and potential biases. The strength of the conclusions depends on the quality of the underlying studies.

Recommendations for Patients

Based on this review, here are practical takeaways for patients — but always remember to discuss any changes with your oncology team:

1. Ask about clinical trials. Many of the promising treatment combinations described in this review are actively being tested in clinical trials. Ask your doctor whether any ongoing trials might be appropriate for your specific situation.
2. Discuss immunotherapy expectations honestly. The evidence shows that immunotherapy alone may have limited benefit for liver metastases. If your doctor recommends immunotherapy, ask how it will be combined with other treatments and what to expect in terms of both benefits and potential side effects.
3. Be aware of combination therapy side effects. Combination immune therapies can cause severe (grade 3–4) toxicity. Ask your doctor about the specific risks and how they will be monitored and managed.
4. Talk to your care team about nutrition. The research on fasting-mimicking diets is preliminary, but real. Do not start a fasting diet on your own — discuss it with your oncologist and a registered dietitian who specializes in cancer care.
5. Stay informed about targeted therapy options. New targeted agents are emerging for liver metastases, including inhibitors of CXCR4, PI3K, and other pathways identified in this review. These may offer options when standard treatments stop working.
6. Know that liver involvement changes the treatment calculus. Because the liver metabolizes drugs and creates immune tolerance, treatments that work well for metastases in other organs may behave differently when the liver is involved. Trust a care team with expertise specifically in liver metastases.

Frequently Asked Questions

Why do breast cancer liver metastases (BCLM) often stop responding to treatment?

BCLM can become resistant because the liver's immune environment is naturally tolerant, allowing cancer cells to escape immune attack. Tumor-supporting cells, metabolic changes, and tiny vesicles also help cancer cells survive chemotherapy, targeted therapy, and immunotherapy. This resistance is common, contributing to an average overall survival of about 31 months.

What is the liver's immune microenvironment, and why does it make immunotherapy less effective?

The liver is full of immune cells but maintains a tolerant environment to avoid reacting to food and bacteria. This tolerance lets cancer cells hide. In mice, liver metastases even draw in and kill cancer-fighting CD8+ T cells, creating a 'systemic immune desert.' That is why immunotherapy alone often fails for liver metastases.

What role do cancer-associated fibroblasts (CAFs) play in drug resistance?

CAFs are the most abundant cells in the tumor microenvironment and produce the extracellular matrix. They can secrete exosomes that increase a molecule called miR-92a-3p in tumor cells, activating the Wnt/beta-catenin pathway. This inhibits cell death and promotes tumor progression and chemoresistance. Activated hepatic stellate cells also confer resistance.

How does the Warburg effect contribute to drug resistance in liver metastases?

The Warburg effect means cancer cells use aerobic glycolysis even when oxygen is plentiful, producing lactic acid. This helps cancer cells adapt to low oxygen but also promotes invasion, blood vessel growth, immune escape, and radioresistance. Additionally, chemotherapy can shift metabolism toward oxidative phosphorylation, increasing resistance in colon cancer liver metastases.

What are extracellular vesicles and how do they spread drug resistance?

Extracellular vesicles are tiny membrane-wrapped packages carrying proteins, lipids, and microRNAs between cells. Cancer-associated fibroblast-secreted exosomes increase miR-92a-3p, activating resistance pathways. Cancer-secreted exosomal miR-4443 promotes liver metastasis, and microRNA-934 induces pro-tumor immune cells. These vesicles communicate resistance among cancer cells.

Are there any dietary changes that might help with breast cancer liver metastases?

One study reported that a fasting-mimicking diet blocked glucose surges and reduced glycogen accumulation in the liver, potentially improving the effect of fulvestrant in BCLM patients. This is preliminary research. Do not start a fasting diet on your own—discuss it with your oncologist and a registered dietitian.

What clinical trials are mentioned for advanced breast cancer or liver metastases?

The review lists ongoing trials, including CXCR4 inhibitors with toripalimab in triple-negative breast cancer, CTLA-4 and PD-1 blockade with radiation-activated NBTXR3, CD47-targeting IMM2902 in HER2-positive tumors, and others targeting EGFR, TGF-beta, Myc, and more. Ask your doctor if any trials fit your situation.

My breast cancer has spread to my liver and I'm worried about drug resistance. Would a second opinion help me find better treatment options?

Drug resistance in breast cancer liver metastases is common, and treatments that work initially often stop working. Research shows that combining treatments targeting different resistance mechanisms may improve outcomes, and many clinical trials are testing new targeted agents for this situation. A second opinion can help review whether your current plan includes all appropriate options, such as combination immunotherapy or targeted therapy, and whether a clinical trial might fit your case. Because the liver's unique immune environment affects treatment response, expert review is especially valuable. Diagnostic Detectives Network provides independent expert second opinions.

Source Information

Original Article: "Mechanisms of drug resistance in breast cancer liver metastases: Dilemmas and opportunities"

Authors: Chun-Yan Yan, Meng-Lu Zhao, Ya-Nan Wei, and Xi-He Zhao

Affiliation: Department of Clinical Oncology, Shengjing Hospital of China Medical University, Shenyang 110022, People's Republic of China

Journal: Molecular Therapy: Oncolytics, Vol. 28, March 2023; pages 212–230 (open access under the CC BY-NC-ND license)

DOI: 10.1016/j.omto.2023.02.001

Corresponding Author: Xi-He Zhao, MD, PhD (zhaoxh@sj-hospital.org)

This patient-friendly article is based on peer-reviewed research. It is intended for educational purposes only and does not constitute medical advice. Patients should consult their healthcare providers about any treatment decisions.