Beyond the Tumor Cell Lung cancer is not just tumor cells - it is an entire ecosystem. Cancer-associated fibroblasts (CAFs) are non-cancerous cells within the tumor microenvironment that are recruited and activated by tumor signals. Once activated, they become powerful allies of cancer cells, reshaping the surrounding tissue to promote tumor growth, spread, and drug resistance.
Why CAFs Matter Now Single-cell RNA sequencing has revealed that CAFs are not a uniform population but a diverse collection of subtypes with distinct origins, molecular profiles, and functions. Some promote tumor growth; some suppress it. Understanding this heterogeneity is essential for developing therapies that target the right CAF subsets.
This Comprehensive Review This systematic review (95 studies after PRISMA screening) synthesizes the latest evidence on CAF origins, heterogeneity, functional roles in NSCLC progression, their communication via extracellular vesicles, and emerging therapeutic strategies to target them.
Clinical Stakes Because CAFs are abundant in NSCLC tumors, highly treatment-resistant themselves, and capable of conferring drug resistance to adjacent cancer cells, they are major contributors to the persistently poor outcomes in advanced NSCLC - making them high-value therapeutic targets.
Origins of CAFs CAFs arise from multiple cell types: normal fibroblasts activated by tumor signals (primarily TGF-beta), mesenchymal stem cells, and even M2 macrophages through a process called macrophage-myofibroblast transition (MMT) driven by Smad3 signaling. This diverse origin contributes to their functional diversity.
Prognostic CAF Subtypes Using multiplex immunohistochemistry and single-cell sequencing, researchers identified 15 distinct CAF subsets in NSCLC. CAF7 (PDGFRB+/FAP+/aSMA+) correlates with poor prognosis and immunosuppressive signatures, while CAF13 is associated with better prognosis. CAF-S5 (FAP+/PDPN+/aSMA-) independently predicts poor survival even after curative resection.
Functionally Distinct CAF Classes Three major functional classes appear across cancers: myofibroblastic CAFs (myCAFs) that stiffen the extracellular matrix; inflammatory CAFs (iCAFs) that secrete immunosuppressive cytokines; and antigen-presenting CAFs (apCAFs) that interact with T cells. These classes have opposite effects on tumor immunity and therapy response.
Organ-Specific Metastasis Roles Even within metastatic NSCLC, different CAF subtypes drive spread to different organs: iCAFs mediate brain metastasis through MET-HGF neural niche remodeling, while apCAFs dominate bone metastasis via SPP1-CD44 signaling. This organotropism suggests subtype-specific therapeutic approaches could prevent specific metastatic complications.
Chemotherapy Resistance CAFs confer cisplatin resistance through multiple mechanisms: ECM remodeling that physically impedes drug penetration, YAP/TAZ-mediated metabolic reprogramming that drives glycolysis in both CAFs and cancer cells, and secretion of HGF that activates cancer cell stemness via the PDL-1 axis.
EGFR-TKI Resistance CAFs are major drivers of resistance to EGFR tyrosine kinase inhibitors in NSCLC. They secrete IGF-1 and HGF that activate bypass signaling through IGF-1R and c-Met, circumventing EGFR inhibition. POSTN secreted by CAFs activates ERK signaling in cancer cells, conferring osimertinib resistance that can be reversed by POSTN knockdown.
Immunotherapy Resistance TGF-beta-secreting CAFs create immune-excluded tumors where T cells cannot penetrate. Myofibroblastic CAFs (myCAFs) and FBLIM1+ CAF subtypes correlate with reduced T cell infiltration and resistance to immune checkpoint inhibitors. In contrast, Meflin+ CAFs favor a positive immunotherapy response.
Radiotherapy Resistance CAFs survive radiation better than cancer cells and can transmit radiation resistance to adjacent cancer cells. Irradiated CAFs upregulate CD73 and CD276, reinforcing adenosine-mediated immunosuppression post-radiation. Targeting senescence-like CAFs with FOXO4-DRI peptide sensitizes NSCLC to radiation therapy.
Extracellular Vesicles as Messengers CAFs communicate with cancer cells and immune cells not only through direct contact and secreted proteins, but also via small extracellular vesicles (sEVs) - nanoscale membrane-enclosed packages that carry miRNAs, lncRNAs, and proteins. These sEVs can travel through the bloodstream, making them both drivers of distant metastasis and potential blood-based biomarkers.
Oncogenic miRNA Cargo CAF-derived sEVs carrying miR-369 promote lung squamous cell carcinoma proliferation by activating MAPK signaling. miR-210 enhances NSCLC migration via PTEN/PI3K/AKT. miR-103a-3p and miR-20a confer cisplatin resistance by suppressing apoptosis through Bak1 and PTEN downregulation, respectively.
lncRNA and Protein Cargo LINC01614 in CAF sEVs enhances glutamine uptake in LUAD cells, fueling metabolic reprogramming that supports aggressive tumor growth. Snail1 protein in CAF sEVs drives epithelial-to-mesenchymal transition in cancer cells. METTL3 in sEVs promotes stemness via m6A RNA modification.
sEVs as Biomarkers THBS2+ CAF-derived sEVs in blood plasma correlate with poor prognosis and immunotherapy resistance. Elevated plasma EV-THBS2 predicts poor disease-free survival, demonstrating the potential of CAF-sEV cargos as accessible liquid biopsy biomarkers that reflect the tumor microenvironment state without requiring tissue biopsy.
Direct CAF Elimination FAP+ CAFs, which correlate with poor prognosis and immunosuppression, are targeted by CAR-NK cells engineered to express FAP-specific chimeric antigen receptors. These cells eliminate FAP+ CAFs via caspase-3/GSDME pyroptosis, reducing tumor growth in preclinical models without requiring direct cancer cell targeting.
Signaling Pathway Inhibition TGF-beta inhibition addresses the central CAF activation pathway, with combined TGF-beta blockade plus immune checkpoint inhibitors showing synergy in restoring anti-tumor T cell responses. Anlotinib, a multi-target tyrosine kinase inhibitor, induces CAF apoptosis and enhances anti-PD1 therapy efficacy by increasing CD8+ T cell infiltration.
The Heterogeneity Challenge The major therapeutic challenge is that eliminating all CAFs would also eliminate tumor-restraining CAF subtypes and disrupt normal tissue homeostasis. Precision targeting of specific pro-tumorigenic CAF subtypes (FAP+, CTHRC1+, POSTN+) while preserving anti-tumor CAF populations requires subtype-specific markers and delivery strategies.
Future Directions The field must clarify CAF plasticity mechanisms (how CAFs transition between subtypes), establish standardized protocols for CAF sEV isolation for clinical diagnostics, develop combination regimens pairing CAF-targeting with immunotherapy, and conduct clinical trials to confirm preclinical therapeutic promise in NSCLC patients.