Tumor-Associated Macrophages Drive Gastric Cancer Progression Through Immune Evasion and Therapeutic Resistance

Gastric cancer (search)Search disease remains one of the most lethal malignancies worldwide, ranking fourth in cancer-related mortality. Despite advances in diagnostic and therapeutic strategies, global incidence and mortality rates have shown only marginal improvement. The tumor microenvironment has emerged as a central orchestrator of tumor initiation, progression, and therapeutic response, with tumor-associated macrophages (search)Search target (TAMs) playing particularly critical roles in gastric cancer pathobiology.

TAMs Drive Gastric Cancer Through Multiple Mechanisms

Within the gastric cancer (search)Search disease microenvironment, TAMs predominantly adopt an M2-like polarization state that facilitates tumor progression through diverse mechanisms. In peritoneal fluid samples from patients with metastatic gastric cancer, researchers have documented significantly elevated proportions of M2-skewed TAMs compared to non-metastatic cases. These macrophages exhibit suppressed antigen presentation and cytotoxicity while overexpressing pro-tumorigenic factors including VEGF (search)Search target, epidermal growth factor, matrix metalloproteinases, and cathepsins.

The phenotypic characteristics of TAMs vary considerably depending on tumor histotype, anatomical compartment, and disease stage, reflecting their plasticity within the evolving tumor ecosystem. Tumor cells actively shape this immune microenvironment by secreting immunomodulatory cytokines such as CCL2, M-CSF, TNF, IL-10View drug details, and TGF-β (search)Search target, thereby amplifying TAM recruitment and M2 polarization through cytokine-mediated feedback loops.

Angiogenesis and Metastatic Facilitation

TAMs serve as potent mediators of vascular remodeling by secreting vascular endothelial growth factors, particularly VEGF (search)Search target-A and VEGF-C, which facilitate blood and lymphatic vessel formation. This activity appears regulated through pathways involving NF-κB (search)Search target and vasohibin-1. Hypoxic stress within the tumor microenvironment induces TAMs to upregulate hypoxia-responsive transcription factors, including HIF-1 and HIF-2, which activate downstream signaling networks driving oncogenic processes.

Hypoxic zones enhance TAM recruitment and activate associated signaling circuits, resulting in increased VEGF (search)Search target secretion and heightened proteolytic activity via matrix metalloproteinases MMP-2 and MMP-9. TAMs have been implicated in facilitating gastric cancer (search)Search disease cell dissemination via the lymphatic system, thereby accelerating both local invasion and distant metastasis. High-mobility group box 1 (HMGB1 (search)Search target), correlated with nodal spread in gastric malignancies, enhances M2-like macrophage polarization by engaging the receptor for advanced glycation end products (RAGE), which augments the invasive capacity of gastric cancer cells.

Immune Evasion Mechanisms

TAMs establish sophisticated immune evasion mechanisms that fundamentally compromise anti-tumor immunity. Notably, TAMs in gastric cancer (search)Search disease lesions exhibit elevated expression of the immune checkpoint receptor PD-1 (search)Search target, a feature absent in adjacent normal tissue. These PD-1+ TAMs adopt an M2-like phenotype, directly engaging PD-L1 (search)Search target-expressing tumor cells and secreting IL-10View drug details, thereby inhibiting CD8+ T cell proliferation and effector function.

Concurrently, TAMs impair dendritic cell maturation by releasing IL-10View drug details and TGF-β (search)Search target, downregulating MHC-II and co-stimulatory molecules (CD80, CD86), and blunting T cell priming. PD-1 (search)Search target+ TAMs also suppress natural killer cell cytotoxicity via TGF-β-mediated repression of perforin and granzyme B. TAMs secrete TGF-β, IL-10, and arginase 1, which collectively inhibit antigen presentation, impair CD8+ T cell function, and promote regulatory T cell expansion.

Exosome-Mediated Communication Networks

Exosome-mediated crosstalk between tumor cells and macrophages reinforces pro-tumoral feedback loops. Gastric cancer (search)Search disease-derived exosomes shuttle regulatory cargo—such as miRNAs and lncRNAs—to reprogram macrophages toward an M2 phenotype. Exosomal miR-155 and miR-21 suppress SOCS1 and PTEN, respectively, driving immunosuppressive polarization and metastatic capacity.

Reciprocally, TAM-derived exosomes potentiate tumor aggressiveness. M2-exosomes enriched with apolipoprotein E remodel the actin cytoskeleton and enhance gastric cancer (search)Search disease cell migration via PI3K/AKT signaling. TAM-derived exosomes also contribute to chemotherapy resistance, with M2-TAMs transferring miR-21 via exosomes to gastric cancer cells, downregulating PTEN and activating the PI3K/AKT cascade to inhibit apoptosis and promote cisplatinView drug details resistance.

Prognostic Implications and Clinical Significance

Meta-analyses confirm that M2 macrophage infiltration correlates with adverse outcomes in gastric cancer (search)Search disease, particularly in the context of heightened TGF-β (search)Search target signaling. In metastatic gastric cancer, increased M2 density, marked by CD204 expression, predicts reduced overall survival and serves as a negative prognostic marker. M2 macrophages are more abundant in poorly differentiated tumors, while signet-ring and mucosal subtypes exhibit lower levels.

Molecular profiling has revealed subtype-specific TAM distributions. CD68+ TAMs are enriched in genomically stable and diffuse-type gastric cancer (search)Search disease, while CD68+CD206+ M1-like TAMs are more common in microsatellite instability and intestinal-type tumors. Single-cell transcriptomics reveals elevated stromal and exhausted cytotoxic T cell populations within tumors relative to adjacent tissue, with TAMs demonstrating substantial functional heterogeneity beyond the M1/M2 dichotomy.

Therapeutic Targeting Strategies

Recent investigations have revealed specific molecules and pharmacologic agents capable of redirecting TAM polarization toward a tumor-inhibitory M1-like phenotype. Methionine enkephalinView drug details (MENK), an endogenous opioid pentapeptide, elevates opioid growth factor receptor expression and inhibits PI3K/AKT/mTOR signaling in both TAMs and gastric tumor cells. This pathway inhibition promotes macrophage repolarization from M2 to M1 phenotype, suppressing cancer cell proliferation and enhancing apoptotic responses.

Low-dose paclitaxelView drug details administration stimulates the TLR4/NF-κB (search)Search target p65 signaling cascade, facilitating phenotypic reprogramming of TAMs in gastric cancer (search)Search disease tissues and leading to enhanced anti-tumor immunity alongside direct cytotoxic effects. The NF-κB signaling pathway, widely implicated in inflammation-driven malignancies, constitutes a critical node in macrophage-mediated tumor support.

Future Therapeutic Directions

Mounting preclinical and translational studies underscore the therapeutic potential of TAM-targeted interventions, particularly those that inhibit TAM recruitment, suppress M2 polarization, or reprogram existing TAMs toward an anti-tumoral M1-like state. Targeting immune checkpoint-expressing TAM subsets or exosome-mediated immunoregulatory circuits may complement existing immunotherapy regimens.

Future research should prioritize high-resolution dissection of TAM heterogeneity via single-cell RNA sequencing and spatial transcriptomics to reveal distinct functional states and regulatory networks within the tumor microenvironment. Special emphasis should be placed on characterizing and therapeutically targeting immune-suppressive subsets such as PD-1 (search)Search target+ and LAYN+ TAMs, which demonstrate strong associations with T cell exhaustion and poor prognosis.

Rationally designed combinatorial regimens that integrate TAM-modulating agents with immune checkpoint inhibitors may synergize to overcome immunotherapy resistance and reinvigorate cytotoxic immune responses. These precision strategies hold promise for reshaping the gastric cancer (search)Search disease immune landscape and improving durable clinical outcomes.