The mechanistic heart of the review is the positive feedback loop it describes between cancer cells, tumor-associated neutrophils and NETs. Tumor cells orchestrate the reprogramming of neutrophils through paracrine signaling: they secrete chemokines such as CXCL1 and CXCL2, which recruit neutrophils via the CXCR1 and CXCR2 receptors, and cytokines including IL-1β, IL-8, granulocyte colony-stimulating factor and tumor-derived exosomes carrying mutant KRAS. Once in the tumor microenvironment, these neutrophils can be pushed toward NET formation by hypoxia, acidity, collagen signaling through DDR1, and stromal inputs from cancer-associated fibroblasts. The NETs themselves then feed back on the tumor, activating pro-growth pathways such as ERK and NF-κB, promoting epithelial-mesenchymal transition and reinforcing the very signals that recruit more neutrophils. This self-amplifying circuit explains why circulating and tumor-infiltrating NETs correlate so consistently with advanced disease in breast, pancreatic, gastric, colorectal and hepatocellular cancers, among others studied to date.

At the molecular level, NET formation, or NETosis, is a carefully choreographed demolition of the neutrophil’s own architecture. In the classical suicidal pathway, signaling through reactive oxygen species generated by the NADPH oxidase complex activates protein arginine deiminase 4, or PAD4, an enzyme that hypercitrullinates histone H3. Citrullination loosens the electrostatic grip of histones on DNA, driving chromatin decondensation, nuclear envelope breakdown and ultimately the explosive extrusion of decondensed DNA decorated with granule proteins. Neutrophil elastase and myeloperoxidase translocate to the nucleus to assist this dismantling, while cathepsin G and proteinase 3 join the final trap. Alternative routes exist as well: viable neutrophils can expel mitochondrial DNA to form traps without dying, and rapid, nuclear-based release has been documented within minutes of certain bacterial encounters. Which pathway dominates appears to depend on the stimulus, a specificity confirmed by comparative proteomic analyses showing that NETs induced by different triggers carry distinct protein cargoes.

As weapons of metastasis, NETs act on several fronts simultaneously. Their DNA scaffolds physically enmesh circulating tumor cells in the bloodstream, increasing adhesion to the vascular endothelium and creating a protective nidus in which disseminated cells can extravasate and colonize distant organs. Proteases embedded in the traps, notably matrix metalloproteinase-9 and neutrophil elastase, remodel the extracellular matrix and, in pancreatic cancer, activate quiescent stellate cells and cancer-associated fibroblasts that prepare fertile ground for micrometastases. Landmark work in mice showed that NETs produced during inflammation can rouse dormant cancer cells, explaining recurrences years after primary tumor removal. The traps also subvert immunity directly: NET-associated DNA can bind TMCO6 on T cells to impair CD8-positive cytotoxic function, upregulate the immunosuppressive enzyme CD73, decorate themselves with PD-L1, promote T cell exhaustion and foster T regulatory cell infiltration. In this sense, NETs function as both physical scaffolds for spread and chemical camouflage against the immune system, a dual role that the review identifies as central to immune evasion and distant metastasis.

The consequences extend to treatment resistance, one of oncology’s most stubborn bottlenecks. NETs generated during chemotherapy confer resistance by activating latent TGF-β, while the dense DNA matrix limits the diffusion of drugs such as doxorubicin, blunting its ability to trigger apoptosis in ovarian cancer cells. In bladder cancer, NETs contribute to radiation resistance, and low-dose ionizing radiation itself can provoke NET extrusion, an unsettling feedback. Immune checkpoint blockade suffers too: NET formation driven by IL-17 signaling mediates resistance in pancreatic cancer, cirrhotic extracellular matrix initiates immunosuppressive NETs that attenuate anti-PD-1 responses in hepatocellular carcinoma, and IGF2BP3-induced NETosis undermines oncolytic virotherapy in malignant glioma. Conversely, the review emphasizes that targeted disruption of the NET axis reverses these resistances and sensitizes tumors to radiotherapy, chemotherapy and checkpoint inhibitors, positioning NETs as genuinely novel therapeutic targets rather than mere biomarkers of misfortune.

A notable theme of the review is the breadth of candidate drugs capable of disarming the NET machinery, many of them repurposed from other fields. Anthracyclines suppress both NADPH oxidase-dependent and -independent NETosis; the antiparasitic ivermectin abrogates NETs and prevents melanoma metastasis in preclinical models; chloroquine and hydroxychloroquine reduce trap formation partly by inhibiting PAD4; and the glucagon-like peptide-1 receptor agonists liraglutide and exenatide enhance checkpoint blockade efficacy by attenuating NETs in lung and liver cancers. Metformin mitigates obesity-driven NET-driven tumor aggressiveness in mice, the nuclear export inhibitor selinexor blocks human NET formation in vitro, and histidine-rich glycoprotein suppresses hepatic metastatic seeding. Even traditional Chinese medicine formulations, from Huang Qin Decoction to Pi Ji Pills, and phytochemicals such as kaempferol, resveratrol, epigallocatechin-3-gallate and emodin, have been shown to interfere with the ROS-PAD4, STAT3-CXCL8 and PI3K-AKT pathways that drive trap formation. Biomaterials approaches, including NET-degrading enzyme hydrogels applied after surgery, and localized photoregulated enzyme delivery, offer physically targeted ways to dismantle traps at metastatic sites.

Translating these discoveries into the clinic depends on measuring NETs reliably, and the review devotes substantial attention to detection technology. The most widely used circulating markers are cell-free DNA, nucleosomes, myeloperoxidase-DNA and neutrophil elastase-DNA complexes, and citrullinated histone H3, the latter quantified by increasingly refined enzyme-linked immunosorbent assays validated in human plasma. Flow cytometric assays allow direct enumeration of NET-bearing structures in blood, atomic force microscopy has resolved the physical architecture of individual traps, and microfluidic chips can capture chromatin fibers from a single drop of blood, while computational image-analysis algorithms now standardize histological quantification. Clinically, peripheral blood NET biomarkers have been associated with diagnosis and progression of malignant tumors, trap-associated CEACAM1 has been proposed as a therapeutic target in metastatic colon cancer, and PD-L1-positive neutrophils releasing NETs in malignant ascites show promise as a hepatocellular carcinoma biomarker. Gene-expression signatures built around NET-related genes and long non-coding RNAs predict prognosis and immunotherapy response across gastric, breast, colon, lung, head-and-neck and soft-tissue cancers, although the review cautions that inconsistent findings and tumor heterogeneity still constrain their deployment.

The prognostic potential is especially striking. Tumor-infiltrating NETs predict post-surgical survival in pancreatic ductal adenocarcinoma, blood NETosis correlates with progression in head and neck cancer, pan-cancer signatures built from NET-associated genes stratify patient outcomes, and a NET-score has emerged as a prognostic marker in colorectal cancer. NETs also influence cancer-associated thrombosis, a major cause of morbidity: tumor-derived exosomes induce NETs that establish hypercoagulability, and IL-1β blockade attenuates thrombosis in NET-dependent breast cancer models. Yet the review is candid about limitations. Detection technologies remain imperfect and poorly standardized, prognostic modeling must contend with heterogeneous patient populations, and some research findings conflict, reflecting context-dependent roles of neutrophil subsets that range from antitumor to pro-tumor. Aging itself alters NET biology, complicating extrapolation from young animal models to elderly patients. Future work, the authors argue, should prioritize optimizing detection methods, conducting rigorous clinical validation and identifying tumor-type-specific therapeutic targets.

The broader message is that the immune defense once celebrated for strangling microbes has become a central hub in cancer biology, one that links inflammation, dormancy, metastasis, thrombosis and treatment failure within a single mechanistic framework. By mapping the regulatory factors, from PAD4 and neutrophil elastase to CXCL chemokines and TGF-β, and by cataloguing both the pharmacological and biomaterial tools that can interrupt them, the review provides a theoretical basis for bringing NETs into precision oncology. If the technical and validation challenges can be overcome, clinicians may one day read a patient’s NET profile the way they now read hormone receptor status, and use NET-disrupting agents to prevent metastasis and sensitize tumors to the therapies already at hand. For now, the convergence of mechanistic insight, assay development and drug repurposing suggests that a web once woven for defense is becoming an actionable thread in the fight against cancer.

Subject of Research: Neutrophil extracellular traps in tumor progression, detection and diagnosis

Article Title: Neutrophil extracellular traps in tumor progression: from mechanistic insights and regulatory factors to clinical detection and diagnosis

Article References: Neutrophil extracellular traps in tumor progression: from mechanistic insights and regulatory factors to clinical detection and diagnosis. (n.d.). https://doi.org/10.1007/s00109-026-02709-2

Image Credits: AI Generated

DOI: 10.1007/s00109-026-02709-2

Keywords: neutrophil extracellular traps, tumor-associated neutrophils, metastasis, immune evasion, therapy resistance, PAD4, cancer biomarkers, tumor microenvironment, diagnosis, checkpoint blockade, NETosis, precision oncology