Hormone-receptor-negative breast cancer—most of it triple-negative, meaning the tumor lacks estrogen receptors, progesterone receptors and surplus HER2—is among the most lethal common subtypes of the disease. It disproportionately strikes younger women and carriers of BRCA1 mutations, grows quickly, and metastasizes early. Once it reaches distant organs, survival is measured in a few years at best, and historically it was counted in months. Recent gains have been incremental at best. Platinum salts and taxanes remain the chemotherapy backbone, and pembrolizumab added to chemotherapy extends life chiefly in the minority of patients whose tumors express the PD-L1 protein at high levels—a biomarker found in fewer than half of metastatic cases. For everyone else, checkpoint inhibitors have offered little. Adding to the challenge, pathologists now recognize that a large share of these apparently HER2-negative tumors are not truly negative: they carry low levels of the HER2 protein on the cell surface, visible as faint immunohistochemical staining, a state the field has termed HER2-low.

HER2-low is defined as cancer scored 1+ on immunohistochemistry, or 2+ with no gene amplification on in situ hybridization—receptor levels once dismissed as biologically irrelevant. Trastuzumab deruxtecan, developed by Daiichi Sankyo and AstraZeneca, changed that view. The drug consists of a trastuzumab antibody tethered through an enzyme-cleavable tetrapeptide linker to deruxtecan, a potent inhibitor of topoisomerase I, an enzyme that dividing cells need to untangle DNA during replication. With roughly eight payload molecules riding on each antibody—a drug-to-antibody ratio far higher than earlier conjugates achieved—the drug delivers a concentrated chemotherapy dose directly to HER2-expressing cells. After the antibody binds its target and is engulfed into the lysosome, tumor-cell enzymes clip the linker, releasing the payload to poison DNA replication. Critically, the released drug is membrane-permeable, so it diffuses into neighboring tumor cells that express little or no HER2. This bystander effect explains why the conjugate works at receptor densities once considered far too low to target, and in earlier randomized studies it roughly doubled progression-free survival compared with standard chemotherapy in pretreated patients with HER2-low metastatic disease.

Durvalumab attacks the tumor from a different direction. The monoclonal antibody binds PD-L1, the molecular brake that tumors and immune cells deploy to shut down cytotoxic T lymphocytes, releasing those cells to resume their attack. The logic for combining it with trastuzumab deruxtecan rests on a decade of tumor immunology showing that antibody-drug conjugates do far more than kill their targets. The DNA damage inflicted by topoisomerase I inhibition can activate the cGAS–STING pathway, the cell’s alarm sensor for misplaced DNA, triggering type I interferon release. Dying tumor cells spill antigens that dendritic cells carry to lymph nodes for T-cell priming, while stressed tumor cells raise the density of MHC class I molecules and PD-L1 on their surface. In laboratory models, topoisomerase I inhibitors effectively behave as an in situ vaccine, converting immunologically cold tumors into inflamed ones that checkpoint inhibitors can exploit. The question BEGONIA posed was whether this mechanistic synergy would hold in human breast cancer, in women receiving both agents as their first treatment for advanced disease.

BEGONIA was conceived as a platform study rather than a single comparison: multiple parallel arms tested durvalumab alongside different investigational partners, including antibodies against CD73 and NKG2A, a STAT3-targeting antisense oligonucleotide, and trastuzumab deruxtecan. The design allowed several drug combinations to be evaluated simultaneously under shared infrastructure, with each arm reporting once it accrued enough patients. The arm reported in Nature Cancer enrolled women with locally advanced, unresectable or metastatic hormone-receptor-negative breast cancer whose tumors were HER2-low and who had not yet received drug therapy for advanced disease. Patients received both agents at established doses on three-week cycles, continuing until their disease progressed or toxicity became unacceptable. Because the study was open-label and lacked a randomized control group, its primary endpoint was the objective response rate—the proportion of patients whose tumors shrank by at least 30 percent, as confirmed by blinded independent central review—together with duration of response, progression-free survival and safety. Enrollment spanned cancer centers across Europe, Asia and North America, capturing the heterogeneity of real-world clinical populations.

The efficacy signals exceeded what either drug’s record alone would predict. Around 62 percent of patients achieved a confirmed objective response, and a small subset saw all detectable disease disappear—complete responses that are rare with conventional first-line chemotherapy in this setting. The median duration of response had not been reached when the data were locked, with the majority of responses still ongoing at analysis and many patients remaining on treatment beyond a year. Notably, responses appeared across the cohort irrespective of tumor PD-L1 expression, hinting that the combination might reach patients who historically derive little benefit from checkpoint inhibition. Disease control—tumors that shrank or remained stable—encompassed the large majority of treated patients. Whether that translates into longer survival will require longer follow-up, but the depth and persistence of the early responses is precisely what caught researchers’ attention in a disease where first-line chemotherapy shrinks tumors in only about a third of cases.

The safety profile combined the known liabilities of both drugs. Toxicities consistent with trastuzumab deruxtecan—nausea, fatigue, hair loss and myelosuppression, particularly anemia and neutropenia—were common, and roughly half of patients experienced grade 3 or worse treatment-related events that required dose interruption or reduction. Durvalumab contributed immune-mediated effects such as thyroid dysfunction and liver enzyme elevations. The toxicity demanding the most vigilance was interstitial lung disease, the inflammatory lung injury recognized as a class effect of trastuzumab deruxtecan across its development program. It occurred in only a small fraction of patients, predominantly at low grade, and was managed with treatment interruption and corticosteroids. No unexpected safety signals emerged, the investigators report, and the pattern of events matched what had been seen when each drug was used alone. Yet because durvalumab can itself provoke pneumonitis, the overlap of two lung-toxicity risks made pulmonary monitoring a central element of the protocol, with clinicians urged to suspect drug-related lung injury in any new respiratory symptom and to treat it early.

The trial was led by Peter Schmid of Queen Mary University of London, with Se Hyun Im of Asan Medical Center in Seoul and Zbigniew Nowecki of the Maria Skłodowska-Curie National Research Institute of Oncology in Warsaw among the senior investigators. Writing in Nature Cancer, the authors describe response rates that compare favorably with historical benchmarks for first-line therapy in hormone-receptor-negative, HER2-low disease, and argue that the pairing’s activity independent of PD-L1 status addresses one of immunotherapy’s persistent blind spots in this subtype. They are careful, however, to frame the study as hypothesis-generating. With a single-arm design and no randomized comparator, the results establish feasibility, response depth and tolerability, but not survival advantage. The authors call for the regimen to be advanced into randomized phase III testing, where durvalumab plus trastuzumab deruxtecan would be measured head-to-head against the current standards of pembrolizumab with chemotherapy and chemotherapy alone.

The results arrive at a moment when the logic of breast cancer sequencing is being rewritten. Trastuzumab deruxtecan is already approved for HER2-low metastatic disease, but only after patients have progressed on earlier lines of therapy; its position has been in the back half of the treatment journey. Moving the drug to the front line, and pairing it with an immunotherapy, raises immediate questions. Do patients who receive the conjugate early forfeit its later benefit if the disease eventually progresses, or does earlier exposure translate into longer survival? How should clinicians handle tumors that are HER2-ultralow, expressing the protein at even fainter levels that current tests barely register? And does the HER2-low label, which depends on subjective immunohistochemistry scoring, reliably identify the right patients when the stakes are a front-line regimen? The HER2-low population is also biologically heterogeneous, mixing immunologically inflamed tumors with cold ones, and translational analyses from BEGONIA are expected to clarify which microenvironments the combination actually reprograms.

For now, the findings stand as a proof of principle: a targeted chemotherapy payload and an immune checkpoint inhibitor can be combined safely and effectively as an initial treatment in one of breast cancer’s most difficult molecular neighborhoods. If randomized trials confirm the kind of survival gains that single-arm data cannot demonstrate, the first-line landscape for hormone-receptor-negative, HER2-low metastatic disease could shift away from cytotoxic chemotherapy toward regimens that couple precision targeting with immune activation—a strategy oncologists have pursued across solid tumors for a decade. The necessary next step—randomized confirmation—will determine whether regulators follow where the biology points. With survival in this population still measured in only a few years, and breast cancer remaining the leading cause of cancer death in women worldwide, the stakes are considerable. The BEGONIA results suggest the tools to change that arithmetic may already be in hand; what remains is to prove, in the rigorous language of randomized evidence, that the promise holds.

The method employed involved the culture of 3D tumor models fashioned from human-derived cells designed to mimic the architecture and complexity of in vivo tumors. By perfusing these tumor constructs with plasma-like fluids laden with various nutrients reflective of specific diets, the team was able to experimentally isolate the effects of distinct dietary components on tumor physiology. While diets rich in insulin, glycerol, and ketones produced negligible morphological changes relative to baseline conditions, exposure to fatty acids and cholesterol induced the formation of hollow, branching tumor extensions. These invasive tendrils are hallmark features of highly metastatic cancers that infiltrate surrounding tissues and facilitate systemic dissemination.

A critical molecular finding centers on the upregulation of matrix metalloproteinase 1 (MMP1), a proteolytic enzyme known for its role in remodeling the extracellular matrix by degrading collagen. Elevated MMP1 levels correlated tightly with the structural remodeling observed in the high-fat diet tumors, suggesting a mechanistic link between dietary lipids and tumor invasiveness. Although causality remains to be definitively established, this association posits MMP1 as a promising therapeutic target for interventions aimed at mitigating fat-induced cancer progression. Future research designed to inhibit MMP1 activity within the context of high-fat systemic environments may yield transformative insights.

Intriguingly, the study also evaluates the impact of ketogenic diets—characterized by high fat but low carbohydrate intake—on breast tumor growth, a nutritional strategy often posited as cancer-protective. Contrary to expectations, the ketogenic nutrient milieu did not confer observable protective effects on the TNBC models. This anomaly highlights the complexity of tumor metabolism and raises the possibility that the putative benefits of ketogenic diets may be contingent upon interactions with other cells or systemic factors absent in the current model system. The heterogeneity of tumors further complicates this paradigm, emphasizing the limitations inherent in model simplification.

The use of 3D microfluidic tumor models represents an elegant balance between biological fidelity and experimental control. Traditional two-dimensional cell cultures offer limited physiological relevance, growing on stiff substrates and lacking multicellular context. Conversely, animal models introduce systemic and environmental complexity that can obscure precise mechanistic elucidation. By integrating physical geometry, matrix stiffness, and physiologically relevant nutrient composition, the microfluidic systems recapitulate key aspects of the tumor niche, enabling interrogation of diet-tumor interactions under controlled yet biologically meaningful conditions.

The observation that tumors exposed to high-fat conditions undergo spatial reorganization—where tumor cells migrate from the core to periphery before invading outward—speaks to the adaptive remodeling capacity of cancer cells under metabolic stress or stimuli. This spatial invasion process, underpinned by molecular shifts such as MMP1 upregulation, typifies the transition from localized disease to invasive carcinomatosis. Understanding the signaling pathways and feedback loops governing this plasticity may reveal intervention points to prevent metastatic spread.

Moreover, the findings suggest that dietary fats do not necessarily accelerate tumor size expansion directly but rather induce qualitative changes in tumor architecture that enhance metastatic potential. This decoupling of growth rate and invasion underscores the multifaceted influence of metabolism on cancer pathogenesis. It suggests that clinical strategies addressing cancer aggressiveness must consider not only tumor proliferation but also the microenvironmental changes that enable metastasis.

This work also contributes to a growing consensus that diet composition exerts profound effects on cancer biology, potentially impacting patient prognosis. By connecting high-fat consumption to gene expression alterations and phenotypic invasiveness, the study advances the understanding of how environmental exposures intersect with tumor biology. It opens avenues for dietary interventions to complement molecular therapies, augmenting the arsenal against aggressive cancers like TNBC.

The research team acknowledges the limitations of their model system, which, while sophisticated, excludes many in vivo complexities such as immune system interactions and stromal cell influences. Tumor heterogeneity and patient variability remain formidable challenges, reinforcing the necessity for diverse model systems and integrative approaches to fully unravel diet-cancer dynamics.

Overall, this pioneering study highlights the detrimental role that dietary fats can play in promoting a more invasive breast cancer phenotype, signaling crucial implications for patients and clinicians alike. It underscores the importance of metabolic context in cancer progression and encourages further explorations into the molecular underpinnings of diet-induced tumor invasiveness. Moving forward, exploiting targets like MMP1 and refining dietary guidelines may inform personalized cancer management strategies aimed at halting metastatic evolution.

Subject of Research: Lab-produced tissue samples

Article Title: Fat promotes growth and invasion in a 3D microfluidic tumor model of triple-negative breast cancer

News Publication Date: 3-Mar-2026

Web References:
http://doi.org/10.1063/5.0291646

References:
Kohram M et al., “Fat promotes growth and invasion in a 3D microfluidic tumor model of triple-negative breast cancer,” APL Bioengineering, March 3, 2026.

Image Credits:
Princeton University

Keywords:
Breast cancer, triple-negative breast cancer, high-fat diets, tumor invasion, matrix metalloproteinase 1, 3D microfluidic tumor models, ketogenic diet, cancer metabolism, tumor microenvironment, cancer aggressiveness, tumor morphology, experimental oncology

Among the many pathways implicated in breast cancer, the PI3K/Akt/mTOR pathway has garnered considerable attention. It serves as a central conduit for growth signals, especially in hormone receptor-positive and HER2-positive breast cancer subtypes. Hyperactivation of this pathway can occur due to various mutations, including alterations in the PIK3CA gene and the loss of the tumor suppressor PTEN. These molecular changes not only drive cancer progression but also contribute to therapeutic resistance, complicating treatment outcomes and necessitating innovative approaches for targeted intervention.

Another noteworthy pathway highlighted in the review is RAS/RAF/MEK/ERK, which is crucial for controlling cell proliferation and survival. Even in the absence of classical mutations, this pathway can become activated under specific conditions, particularly when primary growth signals are obstructed. This phenomenon has been observed in HER2-positive and triple-negative breast cancer cases, where the reliance on alternative pathways becomes evident. Understanding the nuances of these signaling interactions opens avenues for novel therapeutic modalities that can address these challenges directly.

The role of the Wnt/β-catenin signaling pathway is also crucial in breast cancer biology, particularly concerning its involvement in processes such as epithelial-mesenchymal transition (EMT) and metastasis. Activation of this pathway can potentiate the invasive properties of cancer cells, thus enhancing their ability to spread beyond the primary tumor site. Researchers continue to investigate ways to inhibit Wnt signaling to curb metastasis, highlighting a burgeoning avenue for future cancer therapeutics.

The Notch signaling pathway has gained attention for its dual role in development and tumorigenesis. Its activation in breast cancer is implicated in promoting self-renewal of cancer stem cells and driving tumor progression. Exploring targeted therapies that can modulate Notch signaling may provide strategies to not only inhibit tumor growth but also effectively tackle recurrence and resistance, addressing a critical aspect of cancer treatment.

Similarly, the NF-κB signaling pathway is integral to regulating inflammation and immune responses in both normal physiology and cancer. Dysregulation of NF-κB in breast cancer has been linked to enhanced cell survival, further complicating therapeutic efforts. By understanding the mechanisms through which NF-κB contributes to oncogenic processes, researchers can develop innovative strategies to manipulate this pathway, potentially reversing its pro-cancerous effects.

In addition to the aforementioned pathways, the DNA damage response (DDR) pathway plays a pivotal role in maintaining genomic integrity. The review underscores how dysregulation of DDR pathways—often due to mutations in genes like BRCA1 and BRCA2—leads to compromised DNA repair mechanisms, resulting in genomic instability. This aspect of breast cancer biology highlights the potential for targeted therapies that could exploit vulnerabilities in the DDR machinery, offering new therapeutic avenues for treatment-resistant tumors.

The implications of these signaling abnormalities extend beyond understanding cancer biology; they influence the design and efficacy of treatment regimes. With many therapies currently in clinical trials targeting these critical pathways, there is hope that we may soon see healthcare professionals equipped with nuanced, molecule-specific strategies that enhance patient outcomes. Combining modalities that target multiple pathways may yield synergistic effects, ultimately leading to improved therapeutic efficacy and reduced risk of resistance.

Researchers emphasize the importance of personalized medicine in the context of breast cancer treatment. By tailoring therapies to the unique genetic alterations present in individual tumors, oncologists can optimize treatment efficacy while minimizing potential side effects. Such personalized approaches promise to revolutionize breast cancer care, offering hope to patients confronting advanced and treatment-resistant forms of the disease.

The growing understanding of the interplay between various signaling pathways in breast cancer underscores the need for continued research and investment in this field. The pursuit of innovative therapies that target these pathways will be critical as we strive to improve survival rates and quality of life for breast cancer patients. As the scientific community collaborates toward a common goal of unearthing the complexities of tumor biology, we edge closer to a future where breast cancer is not only treatable but manageable.

In conclusion, the critical examination of signaling pathway dysregulation in breast cancer marks a vital step in our journey toward personalized medicine. With researchers like Dinara Ryspayeva and her colleagues at Brown University leading the charge, the prospects for improved therapeutic strategies become increasingly tangible. As we harness these insights, it is our responsibility to advocate for continued funding and support for research initiatives that prioritize patient-centric outcomes in cancer care.

Subject of Research:
Article Title: Signaling pathway dysregulation in breast cancer
News Publication Date: March 25, 2025
Web References: Oncotarget
References:
Image Credits: © 2025 Ryspayeva et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0)
Keywords: breast cancer, signaling pathways, oncogenic mechanisms, personalized medicine, therapeutic strategies, clinical trials.