The concept of M1-TAM and M2-TAM (Figure 1) was initially introduced by Mills et al. (13). The biomarkers CD80, CD86, CD68, and iNOS are up-regulatedly expressed in M1-TAM, which mostly secretes pro-inflammatory cytokines such as TNF-α, IL-6, IL-12, and IL-23 (14). M1-TAM polarization is typically triggered by T helper type 1-associated cytokines, including IFN-γ, TNF-α, LPS, and GM-CSF (15, 16). M1-TAM can limit tumor cell proliferation and augment the anti-tumor immune response by facilitating T cell activation and proliferation in the TME (17).

M2-TAM plays a crucial immunomodulatory role in the TME. The M2-TAM subclassifications are classified into M2a-TAM, M2b-TAM, M2c-TAM, and M2d-TAM based on their specific roles and phenotypic characteristics. The biomarkers CD206, CD209, and Dectin-1 are up-regulatedly expressed in M2a-TAM, which is primarily involved in Th2 immune response. M2a-TAM polarization is typically triggered by IL-4 and IL-13 (18). The biomarkers CD86 and MHC II are up-regulatedly expressed in M2b-TAM, which primarily contributes to the anti-inflammatory and immune regulation by secreting cytokines like TNF-α, IL-6, and IL-10. M2b-TAM polarization is typically triggered by IC and IL-1β. M2c-TAM polarization is typically triggered by GC, TGF-β, and IL-10 (19). The biomarkers CD163, MerTK, and Tie2 are up-regulatedly expressed in M2c-TAM, while CD14, CD86, CD16, and CD206 are down-regulatedly expressed at low levels (20–22). M2c-TAM primarily contributes to tissue remodeling (19). M2d-TAM polarization is typically triggered by adenosine, LIF, and IL-6. M2d-TAM mostly contributes to stimulating angiogenesis and extracellular matrix disintegration to promote tumor spread, with up-regulated expression levels of biomarkers CD14, CD163, ILT2, and ILT3 (23).

In conclusion, the different polarization states of M1-TAM and M2-TAM play various roles in the TME. M1-TAM generally appears as a promoter of anti-tumor immunity, while M2-TAM, through its different subtypes, plays a role in immunosuppression, tissue remodeling, and promoting tumor development.

The increasing application of scRNAseq information in cancer research is enhancing the understanding of tumor biology. scRNAseq information aids in identifying distinct cell subsets and their characteristics, while also revealing cell heterogeneity within tumors. This is particularly important for analyzing the TME and understanding tumor development and metastasis. Seven TAM subtypes are present in nearly all malignancies (Table 1), according to recent widely used scRNAseq analysis studies. These TAM subgroups are named interferon-induced TAM (IFN-TAM), immunomodulatory TAM (Reg-TAM), inflammatory cytokine enriched TAM (Inflam-TAM), lipid-associated TAM (LA-TAM), angiogenic TAM (AngioTAM), tissue-resident TAM (RTM-TAM), and proliferative TAM (Prolif-TAM) based on their signature genes, enrichment pathways, and potential roles (24).

IFN-TAM demonstrates immunosuppressive characteristics while also exhibiting high expression of interferon regulatory genes, including CXCL10, PDL1, and ISG15, similar to M1-TAM (25, 26). Reg-TAM exhibits high expression levels of CX3CR1, MRC1, and TAMARG1. It may possess immunosuppressive properties; however, further research is required to determine its specific functions (27–29). Inflammatory cytokines such as IL1B, CXCL1/2/3/8, CCL3, and CCL3L1 are expressed by Inflam-TAM (25, 30), which is involved in immune cell recruitment and regulation in the inflammatory response associated with tumors (31). By encouraging angiogenesis and metastasis, angiogenic markers, such as VEGFA and SPP1, contribute to the development of tumors, which are highly expressed in the Angio-TAM (25, 30, 32, 33). Lipid-related genes, including APOC1, APOE, ACP5, and FABP5, are highly expressed by LA-TAM and demonstrated active suppression of the anti-tumor immune response (30, 34, 35). RTM-TAM is similar to normal tissue TAM and expresses LYVE1, HES1, and FOLR, which may play a promoting role in tumor invasion and progression (36, 37). The characteristic genes of Prolif-TAM include MKI67 and cell cycle-related genes, which have potential pro-inflammatory functions and play a role in tumor progression (38).

The increasing use of scRNAseq in cancer research is improving the understanding of tumor biology by identifying distinct TAM subclassifications, each with unique gene signatures and roles in tumor development, immune response, and metastasis.

Fibroblast is an essential biological constituent of the TME, with distinct activities and functions between normal and tumor tissues. Normal fibroblast predominantly contributes to the maintainment of tissue architecture and functionality, however, in tumors, it differentiates into cancer-associated fibroblast (CAF), which displays an activated phenotype and facilitates tumor proliferation and dissemination (39). CAF is differentiated from fibroblasts by its contractile properties, metabolic processes, and transcriptomic activity (40, 41). Furthermore, they exhibited elevated levels of FAP, αSMA, and vimentin (42, 43).

In the TME, the interaction between CAF and TAM plays an important role in tumor progression. On the one hand, CAF secrete CXCL12 to regulate M2-TAM polarization (44, 45). In addition, CAFs can also secrete IL-11 to activate the AXL-STAT3 signal transduction pathway, thereby up-regulating M2-TAM polarization (46). TAM, on the other hand, promotes the activation of CAF and enhances the aggressiveness of tumor cells by producing molecules such as IL-6, CXCL12, and TGF-β. In addition, it has been shown that CAF can be derived from M2-TAM, which is called macrophage mesenchymal transformation (MMT). Meanwhile, Smad3 has been found to play a key role in MMT in NSCLC (47).

These complex intercellular signal transduction crosstalk significantly influences the immune environment and metastatic ability of tumors. Therefore, understanding the interaction of CAF and TAM in TME and their signaling pathways is of great significance for tumor therapy.

Mesenchymal stromal cell (MSC) is an undifferentiated, adherent stromal cell present in several organs, frequently located at injury sites and within malignancies (48). MSC can facilitate tumorigenic processes, encompassing tumor tissue creation, maintenance, chemotherapy resistance, and tumor proliferation (48, 49). Recent research indicates that substantial functional interactions may occur between MSC and TAM. Babazadeh et al. discovered that the MSC-derived CXCL12 niche affects TAM polarization dynamics by promoting the phenotypic transformation of BMDMs into M2-TAM, potentially playing a crucial role in the TME (44). Furthermore, Ren et al. demonstrated that extracellular vesicles released by hypoxia-preconditioned MSC enhance NSCLC cell proliferation and motility, as well as M2-TAM polarization, through the transfer of miR-21-5p (50). The investigation of the interplay between MSC and TAM will advance the development of innovative cell treatments for cancer.

Moreover, certain immune cells regulate TAM polarization within the TME by cytokine secretion, consequently influencing immune evasion, metastasis, and treatment resistance of tumors. The miR-320a, released by neutrophils, down-regulates STAT4 upon entering macrophages and facilitates M2-TAM polarization (51). In addition, the expression of signal regulatory protein-α (52) in neutrophils enhances the SHP-1/p38/MAPK/STAT3 signaling pathway and induces M2-TAM polarization (52). IL-17A/IL-17AF released by Th17 cells facilitates NSCLC metastases through the induction of M2-TAM polarization (53). TNFSF15, produced by vascular endothelial cells, inhibits STAT6, resulting in the induction of M1-TAM polarization (54). These pathways offer novel targets and therapeutic approaches for cancer treatment.

Interactions between tumor cells and surrounding cells cause metabolic reprogramming of TME, which impacts tumor development, metastasis, and immune escape. TME is characterized by hypoxia and lactic acid accumulation (55). The absence of oxygen in the TME and the acidic environment alter the metabolism of immune cells and tumor cells, which encourages immune escape and tumor growth (56).

In the TAM of NSCLC, hypoxia can enhance the tumor-supportive role of TAM by boosting iron availability through the upregulation of associated proteins and facilitating the proliferation of malignant cells (7). Furthermore, TAM will release a range of metabolic cytokines, including IL6, TNF-α, and others, in response to hypoxia or a lactic acid environment. These cytokines can encourage the glycolysis of tumor cells (56). TAM increases the intake and synthesis of fatty acids while simultaneously supplying energy for the TCA cycle through the use of alternate metabolites (like glutamine). TME hypoxia is facilitated by this mechanism, which raises lactic acid, NO, reactive oxygen species, and other metabolic byproducts (57).

Continuous angiogenesis in the TME is a multifaceted biological process involving various cell types and molecular pathways. This mechanism is critical for the growth and spread of tumors, as it provides them with the necessary supply of oxygen and nutrients (58). Prior research has established a substantial correlation between TAM infiltration levels and intratumor microvessel counts in NSCLC (59). Recent investigations have demonstrated that TAM can facilitate persistent angiogenesis in NSCLC through various pathways.

Xu et al. indicated that TAM can enhance the proliferation and migration of endothelial cells through the secretion of various angiogenic factors, including VEGF, FGF, and TGF-β, thereby facilitating the formation of new blood vessels (60). Chen et al. (61) observed that the interaction between TAM and tumor cells may up-regulate the expression of IL-8, which increases tumor angiogenesis in NSCLC patients to a great extent. Furthermore, TAM can facilitate matrix remodeling and augment angiogenesis by upregulating matrix metalloproteinases (62). In a hypoxic environment, TAM can activate hypoxia-inducible factor, which subsequently increases the production and secretion of angiogenic factors, thereby sustaining the tumor’s blood supply (63, 64).

The activation of epithelial-mesenchymal transition (EMT) is a critical mechanism in tumor cell metastasis, wherein epithelial cells adopt mesenchymal traits, resulting in increased motility and migration (65). EMT is characterized by the lack of epithelial cell markers and the increased expression of mesenchymal cell markers (66). Numerous studies have indicated that various cytokines and chemokines released by TAM might induce EMT.

A prior study indicated that TGF-β released by TAM can facilitate EMT and increase the expression of SOX9, hence augmenting the proliferation, migration, and invasion of NSCLC cells (67). Moreover, the suppression of TGF-β expression may impede EMT in NSCLC cells (68). Chen et al. (69) discovered that TAM generated from THP-1 exhibited elevated IL-6 expression when co-cultured with NSCLC cells, hence augmenting the invasive capacity of NSCLC cells through the modulation of EMT. Hu et al. (70) did a comparable investigation and discovered that IL-6 released by TAM can activate the JAK2/STAT3 pathway via autocrine signaling, with STAT3 functioning as a transcription factor to enhance the expression of C/EBP-β, so further increasing the transcription and production of IL-6. The establishment of a positive feedback loop involving IL6-STAT3-C/EBP-β-IL6 in TAM facilitates EMT and metastasis in LUAD (70). Suppression of EMT in NSCLC by the inhibition of M2-TAM mediated STAT3 signaling pathway (71). CXCL8 is a chemokine released by M2-TAM. Prior research indicated that CXCL8 may promote EMT and enhance the invasion and migration of NSCLC via the MAPK/NF-κB and JAK2/STAT3 signaling pathways (72, 73).

Immunosuppressive TME is the decisive element for cancer spread, immunological escape, and development of suppressed immune microenvironment. Immune cells are a crucial element of the immune system, regulating the equilibrium between inhibitory and cytotoxic responses in NSCLC (74). Research indicated that TAM can modulate immune surveillance by inhibiting the activity of other immune cells and attracting negative regulatory immune cells.

In the TME of NSCLC, TAM has been shown to enhance the expression of PD-L1, hence suppressing T cell cytotoxicity and phagocytosis, and facilitating T cell exhaustion by increasing the expression of IRF8. Furthermore, Young et al. observed that TAM also impedes the cytotoxicity of NK cells (75). Allavena et al. discovered that M2-TAM secreted immunosuppressive cytokines, such as IL-10 and TGF-β, within the TME, thereby diminishing the population of tumor-infiltrating lung dendritic cells and inhibiting their maturation (76). Regulatory T cells are a subset of T cells that inhibit the immunological response. CCL22 released by TAM promotes immunosuppressive TME by recruitment of Treg and suppresses the immunological function of CD8⁺ T cells, NK cells, B cells, and antigen-presenting cells (77).

One of the most popular and significant treatments for malignant tumors is chemotherapy. Tumor cells frequently become resistant to chemotherapy medications, much like bacteria are readily resistant to antibiotics. Numerous investigations have demonstrated the complex and significant role TAM plays in the development of treatment resistance in NSCLC. In the Lewis lung cancer (LLC) animal model, Hughes et al. discovered that chemotherapeutic drug treatment caused tumor cells to release CXCL12, which improved CD206⁺ TAM invasion, prevented tumor cell death, and aided tumor recurrence (78). By suppressing NEDD4L expression, the exosome miR-3679-5p released by TAM can indirectly stabilize the c-Myc protein, increasing aerobic glycolysis and ultimately fostering cisplatin resistance in NSCLC, according to Wang et al. (79). Furthermore, IL-6 or prostaglandin E2, which induces M2-TAM polarization by activating STAT3, STAT1, and STAT6 signaling pathways, can be secreted by tumor cells in response to cisplatin or carboplatin therapy. And cytotoxic chemotherapy resistance (80, 81).

As translational medicine has advanced, it has become clear that tumor-driven gene mutations use several signaling channel transduction processes to encourage the emergence and growth of malignancies. Although this finding makes tumor-focused therapy possible, likely, drug resistance issues will likely eventually arise with targeted therapy, and we are still working to find a solution (82). According to earlier research, NSCLC cells enhance their resistance to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) by promoting M2-TAM polarization and inhibiting M1-TAM polarization through the transfer of exosomes to TAM by targeting the miR-627-3p/Smads signaling pathway (83). A related work by Wang et al. (84) demonstrated that M2-TAM-generated exosomes regulated the MSTRG.292666.16/miR-6836-5p/MAPK8IP3 axis, hence promoting ocitinib resistance in NSCLC. Targeting TAM has also been demonstrated in studies to lessen acquired resistance to targeted therapy. By blocking the CD47-SIRRPα signal axis and M2 polarization in the co-culture system, Lu et al. discovered that STAT3 inhibitors can increase the phagocytic activity of TAM and decrease the acquired resistance to EGFR-TKIs. Furthermore, gefitinib reduced acquired resistance to gefitinib both in vitro and in vivo when combined with STAT3 inhibitors and anti-CD47 monoclonal antibodies (85).

Therefore, the anticancer activity of chemotherapeutic drugs and targeted agents may be enhanced when treatment is combined with intervention measures that decrease TAM infiltration or inhibit M2-TAM polarization.

Multiple studies have demonstrated that the level of TAM infiltration is directly associated with the prognosis of NSCLC patients (Table 2).

Research indicates that low TAM infiltration indicates a desirable prognosis, whereas high TAM infiltration is associated with an undesirable prognosis (86). For various TAM classifications, high M1-TAM infiltration typically indicates a desirable prognosis, whereas low M1-TAM infiltration is associated with an undesirable prognosis (87). Furthermore, low M2-TAM infiltration (88–95), and low TREM2⁺ TAM infiltration (96) are associated with a desirable prognosis.

Concerning the distribution of TAM in the TME, research indicates that high TAM infiltration in the nest and low TAM infiltration in the stromal typically indicate a desirable prognosis (97–100). Furthermore, high M1-TAM infiltration in the nest is typically correlated with a desirable prognosis (101). In addition, high M1-TAM infiltration in metastatic lymph nodes is regularly associated with a favorable prognosis (102). There is disagreement on the impact of M2-TAM distribution on prognosis. Jackute et al. indicated that low M2-TAM infiltration in both the nest and stroma is typically correlated with a desirable prognosis (103). Whereas Cao et al. (104) indicated that low M2-TAM infiltration in the nest is associated with a desirable prognosis, M2-TAM infiltration in the stroma is not correlated with the prognosis of NSCLC patients. In addition, low infiltration of M2-TAM in the stroma and alveoli correlated with a desirable prognosis (105).

These studies indicate that the infiltration, distribution, and classification of TAM considerably impact the prognosis of NSCLC patients and may serve as potential prognostic biomarkers.

Furthermore, research indicates that TAM is significantly associated with the response to immunotherapy in NSCLC. TREM2⁺ TAM is abundant in several anti-inflammatory cytokines and has an M2-type immunosuppressive phenotype, hence enhancing the inhibition of T-cell activity. TREM2⁺ TAM diminishes the anti-tumor efficacy of CD8⁺ T cells by exacerbating their malfunction and facilitating the development of FOXP3⁺ regulatory T cells. These alterations intensify the mechanism of immune evasion, enabling NSCLC cells to avoid elimination by the host immune system (96). The infiltration of TREM2⁺ TAM was significantly correlated with response rates to immunotherapy. Previous research revealed that patients undergoing PD-1-based immunotherapy with a low percentage of TREM2⁺ TAM in the TME typically exhibited a desirable treatment response rate, which indicates that TREM2⁺ TAM may adversely influence immunotherapy due to its immunosuppressive properties, thereby decreasing the effectiveness of PD-1 inhibitors (96). Decreasing the proportion of TREM2⁺ TAM in the TME may enhance the effectiveness of immunotherapeutic agents like PD-1 inhibitors.

The cytokines and chemokines secreted by TAM substantially influence the prognosis of NSCLC patients by regulating the tumor’s biological features (Table 3).

IL-10, as an immunosuppressive cytokine, can impede the anti-tumor immune response, facilitate tumor immune evasion, and hence expedite tumor development. The research has indicated that upregulated expression of IL-10 in TAM is significantly associated with poorly differentiated NSCLC (106). IL-34 serves as a ligand for the CSF-1R, facilitating the recruitment of TAM and triggering M2-TAM polarization. Baghdadi et al. discovered that in patients with advanced NSCLC, IL-34, by its interaction with CSF-1R, facilitates the M2-TAM polarization, which is significantly associated with tumor immunosuppression and tumor growth (107). Moreover, serum YKL-40 levels have been significantly correlated with the prognosis of NSCLC. Elevated YKL-40 levels are regarded as an independent predictive indicator of worse survival in individuals with metastatic NSCLC. YKL-40 is a glycoprotein that influences the immunological microenvironment of tumors and facilitates their aggressive growth through interactions with immune cells (108). Consequently, the identification of YKL-40 serves as an indicator for assessing the course of NSCLC and may potentially offer significant guidance for personalized treatment (108).

These molecular markers offer novel potential targets for the early diagnosis and prognostic evaluation of NSCLC, along with prospective avenues for future immunotherapy therapies.

Natural compounds exhibit promise in the management of NSCLC by targeting TAM. Numerous natural substances possess anti-tumor activities and can enhance therapeutic outcomes by regulating the function of TAM. Presented are many promising natural compounds together with their modes of action (Table 4).

Several clinical studies have commenced investigating the efficacy of traditional Chinese medicine formulations in patients with NSCLC (Table 5), and initial findings indicate that traditional Chinese medicine may enhance patients’ quality of life and maybe improve outcomes. Wang et al. (137) discovered that Yupingfeng Powder facilitated M1-TAM polarization by enhancing STAT1 phosphorylation, activating CD4⁺ T cells, augmenting their cytotoxicity, and suppressing the in situ development of LLC. Moreover, Bu-Fei decoction, a traditional Chinese medicine formulation, can impede the proliferation, migration, invasion, and immunosuppression of M2-TAM-generated NSCLC by suppressing the production of IL-10 and PD-L1 (138). Jinfu’an decoction facilitates the conversion of M2-TAM to M1-TAM, amplifies the anticancer efficacy of cisplatin, and diminishes the expression of markers associated with M2-TAM. This regulatory action may be associated with the downregulation of β-catenin expression (139). Research on Traditional Chinese Medicine (TCM) aimed at targeting TAM is still developing, necessitating additional clinical trials in the future to validate the effectiveness of TCM formulations and their underlying processes. Simultaneously, in conjunction with contemporary biotechnology, novel active compounds and targets may be identified to facilitate a more efficacious treatment for NSCLC.

Nanomedicine is an innovative product resulting from the integration of nanotechnology and medicine. Increasing emphasis is being directed toward novel pharmaceuticals for the diagnosis, treatment, and prevention of numerous ailments, including tumors and immunological disorders.

Liposomes represent a principal category of anti-tumor nanomedicine and are among the most successful in clinical application (140). Li et al. (141) engineered a folate-modified liposome nanoparticle for the targeted delivery of PFH, STAT3 siRNA, and Fe3O4 to the TME. The dual effect prevented the polarization of M2-TAM in the TME and facilitated their transition into M1-TAM, hence increasing T cell activation and proliferation, which enhanced the immunological response to NSCLC. Tie et al. (142) developed folate-modified liposomes as BIM-S plasmid vectors, which markedly enhanced apoptosis in tumor cells and M2-TAM by specifically targeting NSCLC cells, and substantially suppressed tumor growth in vivo. Zhu et al. (143) created an innovative carboxymethyl chitosan (CMCS)-based nanoparticle (CBT-DC) that targets transferrin receptors on NSCLC cells and accurately modulates the release of docetaxel and curcumin in response to pH and reactive oxygen species (ROS) levels. The findings indicated that CBT-DC had superior anti-tumor efficacy both in vitro and in vivo compared to docetaxel monotherapy and other nanocarriers containing just docetaxel and curcumin. Su et al. (144) developed nanovesicles utilizing microfluidic technology for the delivery of CD47/PD-L1 antibodies. It can only be liberated upon dissociation in the acidic tumor milieu, thereby ameliorating immune-related adverse events, such as anemia, pneumonia, hepatitis, and small intestinal inflammation caused by off-target effects, and facilitating NSCLC-specific activation immunotherapy. Furthermore, Wang et al. (127) developed nanovesicles utilizing oligomeric hyaluronic acid polymers to encapsulate curcumin and baicalin. In vitro cellular assays and in vivo anti-tumor studies on A549 tumor-bearing mice showed that the carrier material targeting nano micelles exhibits significant cytotoxicity and cellular penetration, effective anti-tumor efficacy, and minimal adverse effects. Nanomedicine aimed at TAM offers an innovative approach to the management of NSCLC. By precisely targeting and regulating TAM, nano-agents are anticipated to enhance anti-tumor immune responses and overall treatment effectiveness. The subsequent study ought to concentrate on refining the design and clinical utilization of nanomaterials to enhance therapeutic results.

Conventional therapies for NSCLC mostly encompass radiotherapy, chemotherapy, immunotherapy, and targeted therapy. The combination of targeted TAM therapy with conventional treatments can more effectively modulate the tumor microenvironment and enhance therapeutic outcomes, particularly in patients with advanced or metastatic NSCLC.