Role Of Tumor-associated Macrophages Research Articles

Role of tumor-associated macrophages in relation to angiogenesis in urothelial bladder carcinoma

Background: Urothelial Bladder carcinoma is an aggressive tumor with male predominance. The tumor microenvironment is found to affect tumor progression and biology. One of its main constituents is tumor-associated- macrophages (TAMs). Angiogenesis is a powerful factor in the development of many tumors and is supposed to be induced by tumor cells and some stromal components that regulate tumor behavior. Aim: To assess the correlation of TAMs and angiogenesis in the stroma of urothelial carcinoma and its correlation with the tumor grade and stage and nodal metastasis. Material and Methods: This study was carried out on 30 paraffin blocks of bladder urothelial carcinoma. Hematoxylin and eosin staining was done for confirmation of the histopathological diagnosis. Immunohistochemical staining by CD68 antibody was done for counting of TAMs and CD34 antibodies for tumor-associated angiogenesis (microvessel count). Results: Significant higher TAMs count was detected in high-grade and invasive bladder cancers compared to low-grade and non-invasive types and in patients with nodal metastasis. Moreover, microvessel counts (MVCs) were significantly higher in higher grade, invasive bladder cancers and in patients with nodal metastasis. There was a positive correlation between the predominance of CD68+ TAMs and CD34+ MVCs in urothelial carcinoma. Conclusion: There is a positive correlation between TAMs and angiogenesis in the stroma of urothelial carcinoma and both are positively correlated with tumor grade, stage, and nodal metastasis. Our data indicated that both TAMs and MVCs could serve as prognostic markers for urothelial bladder cancer.

The role of tumor-associated macrophages in osteosarcoma progression - therapeutic implications.

Osteosarcoma (OS) is the most common primary malignant bone tumor. Compared with previous treatment modalities, such as amputation, more recent comprehensive treatment modalities based on neoadjuvant chemotherapy combined with limb salvage surgery have improved the survival rates of patients. Osteosarcoma treatment has, however, not further improved in recent years. Therefore, attention has shifted to the tumor microenvironment (TME) in which osteosarcoma cells are embedded. Therapeutic targets in the TME may be key to improving osteosarcoma treatment. Tumor-associated macrophages (TAMs) are the most common immune cells within the TME. TAMs in osteosarcoma may account for over 50% of the immune cells, and may play important roles in tumorigenesis, angiogenesis, immunosuppression, drug resistance and metastasis. Knowledge on the role of TAMs in the development, progression and treatment of osteosarcoma is gradually improving, although different or even opposing opinions still remain. TAMs may participate in the malignant progression of osteosarcoma through self-polarization, the promotion of blood vessel and lymphatic vessel formation, immunosuppression, and drug resistance. Besides, various immune checkpoint proteins expressed on the surface of TAMs, such as PD-1 and CD47, provide the possibility of the application of immune checkpoint inhibitors. Several clinical trials have been carried out and/or are in progress. Mifamotide and the immune checkpoint inhibitor Camrelizumab were both found to beeffective in prolonging progression-free survival. Thus, TAMsmay serve as attractive therapeutic targets. Targeting TAMs as a complementary therapy is expected to improve the prognosis of osteosarcoma. Further efforts may be made to identify potential beneficiaries of TAM-targeted therapies.

Activation of the GPR35 pathway drives angiogenesis in the tumour microenvironment

ObjectivePrimary sclerosing cholangitis (PSC) is in 70% of cases associated with inflammatory bowel disease. The hypermorphic T108M variant of the orphan G protein-coupled receptor GPR35 increases risk for PSC and...

Role of Tumor-Associated Macrophages in Sarcomas.

Simple SummaryRecent studies have shown the pro-tumoral role of tumor-associated macrophages (TAMs) not only in major types of carcinomas but also in sarcomas. Several types of TAM-targeted drugs have been investigated under clinical trials, which may represent a novel therapeutic approach for bone and soft-tissue sarcomas.Sarcomas are complex tissues in which sarcoma cells maintain intricate interactions with their tumor microenvironment. Tumor-associated macrophages (TAMs) are a major component of tumor-infiltrating immune cells in the tumor microenvironment and have a dominant role as orchestrators of tumor-related inflammation. TAMs promote tumor growth and metastasis, stimulate angiogenesis, mediate immune suppression, and limit the antitumor activity of conventional chemotherapy and radiotherapy. Evidence suggests that the increased infiltration of TAMs and elevated expression of macrophage-related genes are associated with poor prognoses in most solid tumors, whereas evidence of this in sarcomas is limited. Based on these findings, TAM-targeted therapeutic strategies, such as inhibition of CSF-1/CSF-1R, CCL2/CCR2, and CD47/SIRPα, have been developed and are currently being evaluated in clinical trials. While most of the therapeutic challenges that target sarcoma cells have been unsuccessful and the prognosis of sarcomas has plateaued since the 1990s, several clinical trials of these strategies have yielded promising results and warrant further investigation to determine their translational benefit in sarcoma patients. This review summarizes the roles of TAMs in sarcomas and provides a rationale and update of TAM-targeted therapy as a novel treatment approach for sarcomas.

The Role of Tumor Associated Macrophages (TAMs) in Cancer Progression, Chemoresistance, Angiogenesis and Metastasis - Current Status

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The Role of Tumor Associated Macrophages in Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide and represents a classic paradigm of inflammation-related cancer. Various inflammation-related risk factors jointly contribute to the development of chronic inflammation in the liver. Chronic inflammation, in turn, leads to continuous cycles of destruction-regeneration in the liver, contributing to HCC development and progression. Tumor associated macrophages are abundant in the tumor microenvironment of HCC, promoting chronic inflammation and HCC progression. Hence, better understanding of the mechanism by which tumor associated macrophages contribute to the pathogenesis of HCC would allow for the development of novel macrophage-targeting immunotherapies. This review summarizes the current knowledge regarding the mechanisms by which macrophages promote HCC development and progression, as well as information from ongoing therapies and clinical trials assessing the efficacy of macrophage-modulating therapies in HCC patients.

The role of tumor-associated macrophages in primary hepatocellular carcinoma and its related targeting therapy.

Liver macrophages consist of ontogenically distinct populations termed Kupffer cells and monocyte-derived macrophages. Tumor-associated macrophages (TAMs) inhepatocellularcarcinoma (HCC) play a prominent role in tumormicroenvironment by presenting M1(induced by IFN γ along with LPS) and M2(induced by IL-4 and IL13) polarization. Although TAMs are involved in tumor immune surveillance during the course of HCC, they contribute to tumour progression at different levels by inhibiting the anti-tumor immune response, promoting the generation of blood vessels and lymphatic vessels, and supporting the proliferation and survival of tumor cells. In this paper, the multiple functions of TAMs in HCC were reviewed to provide assistance for future researches about therapeutic approaches.

Tumor-associated macrophages are associated with response to neoadjuvant chemotherapy and poor outcomes in patients with triple-negative breast cancer.

Background and objective: Tumor-associated macrophages (TAMs) play an essential role in tumor progression and metastasis. However, the role of TAMs in neoadjuvant chemotherapy (NAC) is unclear and need to be identified. The main subject of this study was to investigate whether TAMs are related to the chemotherapeutic response with triple-negative breast cancers (TNBC).Methods: We retrospectively analyzed pretreatment tissue from patients who received NAC and followed by a mastectomy or breast-conservation for stage II-III TNBC in this study. The association between TAMs and the pathological complete response (pCR) rate of TNBC to NAC was analyzed. In addition, the correlation of the TAMs with recurrence-free survival (RFS) in patients with TNBC was also evaluated.Results: Of the 91 patients, 31 (34.1%) patients experienced pathological complete response (pCR) after completion of NAC. Regarding the chemotheraptic response, patients with low infiltration of CD163+ macrophages achieved a significantly higher rate of pCR. Importantly, Kaplan-Meier survival shown that patients with high infiltration of CD163+ macrophages and non-pCR had poor OS and RFS.Conclusions: our data showed that TAMs may predict chemotherapeutic response and can be used as a promising prognostic candidate for poor survival in TNBC patients treated with NAC.

Tumor‑associated macrophages in lung cancer: Friendly or evil? (Review)

Typically, tumor-associated macrophages (TAMs), an abundant population of leukocytes in lung cancer, are affected by tumor microenvironment (TME) and shift towards either a pro-tumor (M2-like) or an anti-tumor phenotype (M1-like). M2-polarized macrophages, are one of the primary tumor-infiltrating immune cells and were reported to be associated with the promotion of cancer cell growth, invasion, metastasis, and angiogenesis. TAMs are considered a potential target for adjuvant anticancer therapies, and recent therapeutic approaches targeting the M2 polarization of TAMs have shown encouraging results. The present review discusses recent developments in the role of TAMs in cancer, in particular TAMs functions, clinical implication and prospective therapeutic strategies in lung cancer.

Tumor-associated macrophages: Role in the pathological process of tumorigenesis and prospective therapeutic use (Review).

The aim of the present study was to evaluate the current body of knowledge regarding tumor-associated macrophages (TAMs) and their potential use in antitumor therapy, based on their role in the pathological process of tumorigenesis. For this purpose, a critical analysis of published data and summarization of the findings available from original studies, focusing on the role of TAMs in the pathological process, and their potential therapeutic application was performed. Promising key avenues of research were identified in this field. The following issues seem the most promising and thus worth further investigation: i) The process of M1/M2 macrophage polarization, macrophage characteristics at intermediate polarization steps and their role in the tumor process; ii) determining the conditions necessary for transitions between the M1 and M2 macrophage phenotypes and the role of signals from the microenvironment in this process; iii) cause-and-effect associations between the quantity and quality of macrophages, and the prognosis and outcome of the pathological process; iv) modulation of macrophages and stimulation of their phagocytic activity with drugs; v) targeted vector-based systems for drug delivery to macrophages; and vi) targeted drug delivery systems with macrophages as carriers, thus potentially combining chemotherapy and immunotherapy.

Tumor-Associated Macrophages: Protumoral Macrophages in Inflammatory Tumor Microenvironment.

Tumor microenvironment consists of malignant and non-malignant cells. The interaction of these dynamic and different cells is responsible for tumor progression at different levels. The non-malignant cells in TME contain cells such as tumor-associated macrophages (TAMs), cancer associated fibroblasts, pericytes, adipocytes, T cells, B cells, myeloid-derived suppressor cells (MDSCs), tumor-associated neutrophils (TANs), dendritic cells (DCs) and Vascular endothelial cells. TAMs are abundant in most human and murine cancers and their presence are associated with poor prognosis. The major event in tumor microenvironment is macrophage polarization into tumor-suppressive M1 or tumor-promoting M2 types. Although much evidence suggests that TAMS are primarily M2-like macrophages, the mechanism responsible for polarization into M1 and M2 macrophages remain unclear. TAM contributes cancer cell motility, invasion, metastases and angiogenesis. The relationship between TAM and tumor cells lead to used them as a diagnostic marker, therapeutic target and prognosis of cancer. This review presents the origin, polarization, role of TAMs in inflammation, metastasis, immune evasion and angiogenesis as well as they can be used as therapeutic target in variety of cancer cells. It is obvious that additional substantial and preclinical research is needed to support the effectiveness and applicability of this new and promising strategy for cancer treatment.

Inverse correlation between Interleukin-34 and gastric cancer, a potential biomarker for prognosis

BackgroundGastric cancer (GC) is a malignancy with high morbidity/mortality, partly due to a lack of reliable biomarkers for early diagnosis. It is important to develop reliable biomarker(s) with specificity, sensitivity and convenience for early diagnosis. The role of tumour-associated macrophages (TAMs) and survival of GC patients are controversial. Macrophage colony stimulating factor (MCSF) regulates monocytes/macrophages. Elevated MCSF is correlated with invasion, metastasis and poor survival of tumour patients. IL-34, a ligand of the M-CSF receptor, acts as a “twin” to M-CSF, demonstrating overlapping and complimentary actions. IL-34 involvement in tumours is controversial, possibly due to the levels of M-CSF receptors. While the IL-34/M-CSF/M-CSFR axis is very important for regulating macrophage differentiation, the specific interplay between these cytokines, macrophages and tumour development is unclear.MethodsA multi-factorial evaluation could provide more objective utility, particularly for either prediction and/or prognosis of gastric cancer. Precision medicine requires molecular diagnosis to determine the specifically mutant function of tumours, and is becoming popular in the treatment of malignancy. Therefore, elucidating specific molecular signalling pathways in specific cancers facilitates the success of a precision medicine approach. Gastric cancer tissue arrays were generated from stomach samples with TNM stage, invasion depth and the demography of these patients (n = 185). Using immunohistochemistry/histopathology, M-CSF, IL-34 and macrophages were determined.ResultsWe found that IL-34 may serve as a predictive biomarker, but not as an independent, prognostic factor in GC; M-CSF inversely correlated with survival of GC in TNM III–IV subtypes. Increased CD68+ TAMs were a good prognostic factor in some cases and could be used as an independent prognostic factor in male T3 stage GC.ConclusionOur data support the potency of IL-34, M-CSF, TAMs and the combination of IL-34/TAMs as novel biological markers for GC, and may provide new insight for both diagnosis and cellular therapy of GC.

Glycosylated Nanoparticles Derived from RAFT Polymerization for Effective Drug Delivery to Macrophages.

The functional group tolerance and simplicity of reversible addition fragmentation chain transfer (RAFT) polymerization enable its use in the preparation of a wide range of functional polymer architectures for a variety of applications, including drug delivery. Given the role of tumor-associated macrophages (TAMs) in cancer and their dependence on the tyrosine kinase receptor FMS (CSF-1R), the key aim of this work was to achieve effective delivery of an FMS inhibitor to cells using a polymer delivery system. Such a system has the potential to exploit biological features specific to macrophages and therefore provide enhanced selectivity. Building on our prior work, we have prepared RAFT polymers based on a poly(butyl methacrylate-co-methacrylic acid) diblock, which were extended with a hydrophilic block, a cross-linker, and a mannose-based monomer scaffold, exploiting the abundance of macrophage mannose receptors (MMRs, CD206) on the surface of macrophages. We demonstrate that the prepared polymers can be assembled into nanoparticles and are successfully internalized into macrophages, in part, via the MMR (CD206). Finally, we showcase the developed nanoparticles in the delivery of an FMS inhibitor to cells, resulting in inhibition of the FMS receptor. As such, this study lays the groundwork for further drug-delivery studies aimed at specifically targeting TAMs with molecularly targeted therapeutics.

Metabolic dysfunction and early-onset colorectal cancer - how macrophages build the bridge.

BackgroundThe incidence of colorectal cancer (CRC) among patients <50 years of age has increased dramatically over the last decades. At the same time, the growing proportion of obese children and adolescents and the increasing proportion of young and obese patients with CRC suggests an association between metabolic dysfunction and carcinogenesis. Tumor‐associated macrophages (TAMs) are able to orchestrate tumor promoting and suppressing mechanisms in CRC. The aim of this review was to discuss the different roles of TAMs in CRC and their phenotype‐specific metabolic pathways to identify potential new targets for CRC treatment.MethodsA literature search was performed using PubMed, Cochrane and Embase to identify studies on TAMs and their metabolism in CRC. The following search terms were used in various combinations: (obesity OR adiposity OR obese) AND (macrophage OR polarization OR macrophage metabolism) AND ((colon cancer*) OR (colon carcinoma) OR (colonic tumor*) OR (colonic neoplasm[MeSH]) OR (rectal cancer*) OR (rectal carcinoma) OR (rectal tumor*) OR (rectal neoplasm[MeSH]) OR (colorectal cancer*) OR (colorectal carcinoma) OR (colorectal tumor*) OR (colorectal neoplasm[MeSH])). Studies including data on the phenotype and metabolism of TAMs in CRC were analyzed.ResultsEvidence for the prognostic utility of macrophage markers in CRC is currently evolving, with a particular role of stage‐dependent cellular metabolism profiles of TAMs. Itaconate is one of the metabolites produced by proinflammatory subtypes of TAMs and it is known to have tumor promoting effects. Metabolic pathways that are involved in macrophage activation and reprogramming play a role in a chronic inflammatory setting, consequently affecting the onset and development of CRC.ConclusionsTumor‐promoting metabolites, such as itaconate, are directly regulating these mechanisms, thereby triggering carcinogenesis. Metabolic reprogramming in TAMs can build a bridge between metabolic dysfunction and the onset and progression of CRC through inflammatory pathways, particularly in younger patients with early‐onset CRC.

The prognostic and clinicopathological value of tumor-associated macrophages in patients with colorectal cancer: a systematic review and meta-analysis.

There is a growing literature on the significance of tumor-associated macrophages (TAMs) in colorectal cancer (CRC). However, the role of TAMs in predicting the prognosis of CRC remains controversial. The current study aims to determine the prognostic and clinicopathological value of different types and distribution of TAMs in CRC. A comprehensive literature search of PubMed, Embase, and Cochrane Library databases was conducted from the inception to 1 September 2019. The correlations of TAMs with overall survival (OS), disease-free survival (DFS), cancer-specific survival (CSS), and clinicopathological characteristics were analyzed. A total of 5,575 patients from 29 studies were included in this meta-analysis. The pooled hazard ratios (HRs) indicated that high density of pan-macrophages in tumor invasive margin (IM) was associated with better OS (HR = 0.57, 95%CI = 0.38-0.85), DFS (HR = 0.32, 95%CI = 0.19-0.52), and CSS (HR = 0.56, 95%CI = 0.41-0.77). Moreover, the high density of pan-macrophages in tumor center (TC) was correlated with better DFS (HR = 0.66, 95%CI = 0.45-0.96). However, high expression of M2 macrophages in TC was associated with poor DFS (HR = 2.42, 95%CI = 1.45-4.07) and CSS (HR = 1.74, 95%CI = 1.24-2.44). High M2 macrophages density in IM was also associated with short DFS (HR = 2.81, 95%CI = 1.65-4.77). In addition, the results showed that high density of pan-macrophages in IM was associated with no tumor metastasis, while high M2 macrophages density in TC was correlated with poor tumor differentiation. High Pan-TAMs density in IM has a positive effect on the prognosis of CRC patients, while high density M2 macrophage infiltration in TC is a strong indicator of poor prognosis.

Macrophages confer resistance to BET inhibition in triple-negative breast cancer by upregulating IKBKE

BET inhibitors (BETi) exhibit a strong anti-tumor activity in triple-negative breast cancer (TNBC). However, BETi resistance has been reported in TNBC. The mechanisms of resistance have not been demonstrated. Tumor-associated macrophages (TAMs) are frequently involved in cancer cells resistance to chemotherapy, also associated with poor prognosis in TNBC. However, the role of TAMs in BETi resistance remains unknown. Here, we found that BETi JQ1 and I-BET151 exerted anti-tumor effects in TNBC by decreasing IKBKE expression to attenuate NF-κB signaling. TAMs have been reported to associate with chemoresistance in breast cancer. Here, we firstly found that TNBC-stimulated TAMs activated NF-κB signaling by upregulating IKBKE expression to enhance breast cancer cells resistance to BETi. The IKBKE levels were also proved to be higher in clinical TNBC tissues than Non-TNBC tissues, suggesting feedback induction of IKBKE expression by TNBC-stimulated TAMs in TNBC. Moreover, the induction of IKBKE by TAMs in TNBC cells was identified to be associated with STAT3 signaling, which was activated by TAM-secreted IL-6 and IL-10. Lastly, the combination of inhibitors of BET and STAT3 exerted a synergistic inhibition effects in TAM-cocultured or TAM CM-treated TNBC cells in vitro and in vivo. Altogether, our findings illustrated TNBC-activated macrophages conferred TNBC cells resistance to BETi via IL-6 or IL-10/STAT3/IKBKE/NF-κB axis. Blockade of IKBKE or double inhibition of BET and STAT3 might be a novel strategy for treatment of TNBC.

Arginase-1+ Exosomes from Reprogrammed Macrophages Promote Glioblastoma Progression.

Interactions between tumor cells and tumor-associated macrophages (TAMs) are critical for glioblastoma progression. The TAMs represent up to 30% of the glioblastoma mass. The role of TAMs in tumor progression and in the mechanisms underlying tumor growth remain unclear. Using an in vitro model resembling the crosstalk between macrophages and glioblastoma cells, we show that glioblastoma-derived exosomes (GBex) reprogram M1 (mediate pro-inflammatory function) and M2 (mediate anti-inflammatory function) macrophages, converting M1 into TAMs and augmenting pro-tumor functions of M2 macrophages. In turn, these GBex-reprogrammed TAMs, produce exosomes decorated by immunosuppressive and tumor-growth promoting proteins. TAM-derived exosomes disseminate these proteins in the tumor microenvironment (TME) promoting tumor cell migration and proliferation. Mechanisms underlying the promotion of glioblastoma growth involved Arginase-1+ exosomes produced by the reprogrammed TAMs. A selective Arginase-1 inhibitor, nor-NOHA reversed growth-promoting effects of Arginase-1 carried by TAM-derived exosomes. The data suggest that GBex-reprogrammed Arginase-1+ TAMs emerge as a major source of exosomes promoting tumor growth and as a potential therapeutic target in glioblastoma.

Obesity-Associated Leptin Signaling Promotes Chemotherapy Resistance in Basal-Like Breast Cancer: The Role of Tumor-Associated Macrophages

Abstract Objectives Obesity is associated with a reduced response to cytotoxic chemotherapies. Given that the adipokine leptin has been shown to promote macrophage production of pro-tumor cytokines, we hypothesized that leptin-induced pro-tumor macrophage polarization is a key mediator of obesity-associated docetaxel resistance. Methods Wild-type C57BL/6 mice were fed a low-fat control (10% kcal from fat) or high-fat diet-induced obesity (DIO; 60% kcal from fat) diet for 15 weeks, then orthotopically injected with 2 mouse mammary tumor cell lines: EWnt-S (scrambled shRNA) and EWnt-L (shRNA to the leptin receptor) in the 9th and 4th mammary glands, respectively. Mice in each group were then randomized to vehicle or docetaxel (20 mg/kg/week IV for 3 weeks). The transcriptomes of both tumors (n = 6/group) were analyzed by microarray, and cell type enrichment analysis performed using the webtool xCell. The in vitro effects of leptin +/− docetaxel on macrophage polarization as well as cancer cell cytotoxicity and markers of invasive capacity are currently being assessed. Results The DIO mice had greater body weight and % body fat at euthanization versus control mice (P &amp;lt; 0.01 for both). Docetaxel treatment in DIO mice reduced tumor growth rate in EWnt-L tumors (P &amp;lt; 0.05), but not EWnt-S tumors. In contrast, docetaxel treatment reduced the EWnt-L and EWnt-S tumor growth rate in control mice (P &amp;lt; 0.05 for both). xCell analysis indicated that docetaxel treatment increased M2 macrophage levels in the DIO mouse tumors, but not the controls. Leptin receptor knockdown attenuated this effect. In addition, key genes related to “macrophage markers”, “cytokines and inflammatory response”, and “interleukin (IL)-6 signaling” were differentially expressed in docetaxel-treated EWnt-S tumors from DIO versus control mice. Conclusions These results indicate that leptin signaling mediates obesity-induced docetaxel resistance in the E-Wnt model of basal-like breast cancer. They also suggest that docetaxel interacts with leptin signaling to promote an increase in tumor-promoting M2 macrophages and subsequent docetaxel resistance. This hypothesis is currently being explored through our in vitro studies. Funding Sources This work was supported by a grant from the Developmental Funding Program, Lineberger Comprehensive Cancer Center, UNC Chapel Hill.

The Role of Tumor-Associated Macrophages in the Progression and Chemoresistance of Ovarian Cancer.

Tumor-associated macrophages (TAMs) constitute the main population of immune cells present in the ovarian tumor microenvironment. These cells are characterized by high plasticity and can be easily polarized by colony-stimulating factor-1, which is released by tumor cells, into an immunosuppressive M2-like phenotype. These cells are strongly implicated in both the progression and chemoresistance of ovarian cancer. The main pro-tumoral function of M2-like TAMs is the secretion of a variety of cytokines, chemokines, enzymes and exosomes that reach microRNAs, directly inducing the invasion potential and chemoresistance of ovarian cancer cells by triggering their pro-survival signaling pathways. The M2-like TAMs are also important players in the metastasis of ovarian cancer cells in the peritoneum through their assistance in spheroid formation and attachment of cancer cells to the metastatic area—the omentum. Moreover, TAMs interplay with other immune cells, such as lymphocytes, natural killer cells, and dendritic cells, to inhibit their responsiveness, resulting in the development of immunosuppression. The detrimental character of the M2-like type of TAMs in ovarian tumors has been confirmed by a number of studies, demonstrating the positive correlation between their high level in tumors and low overall survival of patients.

Macrophage targeting in cancer.

Tumorigenesis is not only determined by the intrinsic properties of cancer cells but also by their interactions with components of the tumor microenvironment (TME). Tumor-associated macrophages (TAMs) are among the most abundant immune cells in the TME. During initial stages of tumor development, macrophages can either directly promote antitumor responses by killing tumor cells or indirectly recruit and activate other immune cells. As genetic changes occur within the tumor or T helper 2 (TH 2) cells begin to dominate the TME, TAMs begin to exhibit an immunosuppressive protumor phenotype that promotes tumor progression, metastasis, and resistance to therapy. Thus, targeting TAMs has emerged as a strategy for cancer therapy. To date, TAM targeting strategies have focused on macrophage depletion and inhibition of their recruitment into the TME. However, these strategies have shown limited therapeutic efficacy, although trials are still underway with combination therapies. The fact that macrophages have the potential for antitumor activity has moved the TAM targeting field toward the development of TAM-reprogramming strategies to support this antitumor immune response. Here, we discuss the various roles of TAMs in cancer therapy and their immunosuppressive properties, as well as implications for emerging checkpoint inhibitor-based immunotherapies. We review state-of-the-art TAM-targeting strategies, focusing on current ones at the preclinical and clinical trial stages that aim to reprogram TAMs as an oncological therapy.