Mechanistic insight into the immunomodulatory effects of polyphenols on breast cancer: A pharmacotherapeutic perspective (Review)

1. Introduction

Breast cancer (BC) remains the second leading cause of mortality among women globally, with 2.29 million cases reported in 2022(1). Despite advances in diagnosis and treatment, subtypes such as triple-negative BC (TNBC) present significant therapeutic challenges due to the lack of approved treatment methods and poor prognoses. While tumors that are human epidermal growth factor receptor 2 (HER2)-amplified or positive for hormone receptors respond well to targeted therapy, TNBC lacks these targets and remains aggressive and difficult to treat (2,3). The second edition of Hanahan and Weinberg's ‘Hallmarks of Cancer’ added a new hallmark: Evading immune response, which highlighted the crucial game of ‘hide-and-seek’ taking place between the immune system and cancer (4). As a result, biologically conversant therapies, such as immunotherapy, are viewed as a promising approach; however, immune-related toxicities and variable efficacy across BC subtypes are some of the drawbacks associated with this therapy (2,5). Therefore, it is crucial to identify an affordable alternative that can rapidly transition from the laboratory to the patient with the least amount of added toxicity. According to epidemiological research, a nutritious diet high in fruits and vegetables is related to a lower prevalence of BC (6,7). Polyphenols, widely abundant in fruits and vegetables, in addition to having antioxidant, anti-viral, and anti-bacterial properties, have exhibited potential as anticancer agents through their immunomodulatory properties (8,9). The present review discusses BC treatment options with a particular emphasis on immunotherapy and the potential of polyphenols as immunotherapeutic agents.

2. Cancer immunology, breast tumor microenvironment and current immunotherapy landscape

The immune system consists of innate and acquired immunity, working together for immunological surveillance (10,11). Innate immunity constitutes the primary defense of an organism through physical barriers, temperature, pH and cells such as neutrophils and macrophages, with cytokines regulating these processes. Acquired immunity provides immunity to foreign bodies by producing B-cell antibodies and activating cytotoxic T-cells with the aid of antigen-presenting cells (APCs). Although cancer cells arise from self-tissue, they are characterized by distinct biochemical composition, antigenic structure and physiological function in comparison to the healthy cells that render them detectable by immune cells. However, cancer cells are characterized by a process known as immunoediting, by which tumor cells subsequently develop strategies with which to elude destruction by the immune system (12). Immunoediting encompasses three dynamic phases: Immunosurveillance, where cancer cells are eliminated by immune cells; equilibrium, where tumor cells that were not eliminated coexist with the immune system; and evasion, where resistant cells outmaneuver the immune system through various evasion tactics (13,14). These include tumor-induced immune suppression by overexpressing immune checkpoint molecules, such as programmed death-1/ligand 1 (PD-1/L1) and cytotoxic T-lymphocyte (CTL) antigen-4 (CTLA-4), and producing immunosuppressive substances, such as interleukin (IL)-10, transforming growth factor (TGF), and alpha-fetoprotein, which inhibit innate immune responses to cancer. Tumor-specific CTLs may undergo genetic modification to become resistant to the TGF-inhibitory action. Tumors may activate Fas ligand (FasL) and cause tumor-infiltrating effector T-cells to undergo apoptosis (15).

The BC immune tumor microenvironment is a dynamic landscape consisting of both immune-promoting and immunosuppressive factors (10). Although BCs were considered typically less immunogenic than melanoma or lung cancer, recent studies have demonstrated significant immune involvement in subtypes such as TNBC (16). The evasion of BC cells involves intricate mechanisms, such as the recruitment and polarization of M2-phenotype tumor-associated macrophages (TAMs), which promotes cell survival through the secretion of TGF-β, IL-10 and CCL18(17). Myeloid-derived suppressor cells (MDSCs) may also suppress natural killer (NK) cells and T-cells by the induction of oxidative stress and the release of pro-angiogenic factors, such as vascular endothelial growth factor, IL-10, matrix metalloproteinases and TGF-β (18). Furthermore, regulatory T-cells (Tregs) play a role in the ability of MDSCs to suppress the immune system. Forkhead box P3 (Foxp3)-expressing Tregs are potent inducers of peripheral immunological tolerance, suppressing a range of immune cells, including CD4+ and CD8+ T-cells, NK-cells, NK T-cells, B-cells and APCs through IL-10, TGF-β and checkpoint ligand CTLA-4 expression (19,20). These interactions have been described in detail by Moura et al (16). Moreover, the suppression of NK cells and natural killer group 2 member D protein (NKG2D) receptors via the upregulation of human leukocyte antigen-G and PD-L1 on tumor cells and the secretion of TGF-β, respectively, disarms these cells from tracking down tumor cells (16). Understanding these interactions, will pave the way towards developing effective targeted therapies that could reprogram the immune ecosystem and increase therapeutic response.

Recent trends in BC immunotherapy have exhibited a strategic shift from monotherapy towards multi-modal approaches (Fig. 1). Immune checkpoint inhibitors (ICIs) targeting PD-1/L1 that were once limited to TNBC, are being investigated across BC subtypes, often in combination with chemotherapy, and have demonstrated enhanced efficacy (21,22). TNBCs and HER2+ subtypes often benefit more from the early administration of ICIs (23), while clinical trials demonstrate enhanced outcomes with combination therapies like nivolumab with ipilimumab for TNBCs and durvalumab with tremelimumab for metastatic HER2-negative BCs (24-26). While monoclonal antibodies remain central to the management of HER2+ cancers, emerging modalities, such as bispecific antibodies and chimeric antigen receptor T-cell therarpy combat cancer through tumor-specific targeting (27,28). Cancer vaccines have also emerged as a promising strategy; however, they still face inconsistencies in immune activation (29) Across all modalities, cytokine-based and other immunomodulatory drugs play a crucial role in sustaining T-cell and NK cell responses but may induce systemic toxicity (30). The recurring pattern is strong: Although immunotherapies are improving constantly, their success is limited by toxicity and resistance. Even in BC, the side-effects of conventional immunotherapy agents may manifest mild symptoms, such as nausea and neutropenia to life-threatening hepatitis, mucosal inflammation and septic shock (31). Hence, there is a growing need for alternative strategies that can mitigate the adverse effects, while retaining or enhancing their therapeutic efficacy in cancer. Epidemiological studies have suggested that maintaining a nutritious diet of fruits and vegetables rich in phytochemicals, such as polyphenols are associated with a reduced prevalence of BC (6,7).

Figure 1 Illustration of the different types of immunotherapies, namely immune checkpoint inhibitors, monoclonal antibodies, T-cell therapy, vaccines and immune system modulators. CTLA-4, cytotoxic T-lymphocyte antigen-4; PD-L1, programmed cell death ligand protein 1; HER2, human epidermal growth factor receptor 2; HER2, human epidermal growth factor receptor 2; CAR-T, chimeric antigen receptor T-cell; IFN, interferon.

3. Immunogenic cell death

An emerging concept in cancer immunology is immunogenic cell death (ICD). It involves alterations in cell surface chemistry and the release of ‘danger signals’, namely as damage-associated molecular patterns, such as high mobility group box 1, heat shock proteins and calreticulin, initiating dendritic cell (DC) and T-cell responses (32,33). A detailed discussion on ICD is provided in the study by Arimoto et al (34). In their study, they outline the mechanistic insights, particularly within the context of cancer immunotherapy (34). In terms of immunogenicity, most solid tumors are considered ‘cold tumors’ with impaired immunological responses. ICD induction can be used to inflame the tumor microenvironment to increase its immunogenicity (35). Contrary to the belief that chemotherapy acts as an immunosuppressant, certain drugs, such as anthracyclines (e.g., doxorubicin and mitoxantrone) and oxaliplatin can trigger ICD (36,37). However, the use of chemotherapeutic drugs is associated with toxicity; hence, it may be hypothesized that non-toxic agents, such as polyphenols may be used to trigger ICD and amplify immune responses. Understanding these mechanisms at a molecular level is crucial for refining therapeutic strategies and improving treatment outcomes. Polyphenols target various pathways and molecules to modulate and regulate immune system to target cancer cells, as illustrated in Fig. 2.

Figure 2 Illustration of the immunomodulation of breast cancer using different pathways; immunomodulatory cells such as T-cells, MDSCs, Tregs and macrophages; modulation of immune checkpoints, such as PD1. PD-L1 and CTLA-4; modulation of inflammatory cytokines and interferons; modulation of innate and adaptive immunity; and modulation of pathways. MDSCs, myeloid-derived suppressor cells; CTLA-4, cytotoxic T-lymphocyte antigen-4; PD-L1, programmed cell death ligand protein 1; IL, interleukin; IFN, interferon; MCP-1, monocyte chemoattractant protein 1; M-CSF, macrophage colony-stimulating factor; ASC, apoptosis-associated speck-like protein containing a CARD; IFI16, interferon-induced protein 16; TAM, tumor-associated macrophage; MMP, matrix metalloproteinase; Foxp3, forkhead box P3; TLR, Toll-like receptor; NK, natural killer; DNMT, DNA methyltransferase; HRNR.

4. Immunomodulatory effects of polyphenols in breast cancer

Polyphenols are known to exert positive benefits on cardiovascular and inflammatory diseases, diabetes and aging. Accumulating evidence also highlights their protective effects against cancer by inducing anti-proliferative, anti-inflammatory, antioxidant, cytotoxic and immunomodulatory effects (38,39). Multiple studies have demonstrated that phytochemicals (classified as demonstrated in Fig. 3), particularly polyphenols, such as resveratrol, quercetin, genistein and curcumin, are involved in the modulation of the immune system and regulation of the innate and adaptive immune system to provide beneficial anticancer outcomes (9) (Figs. 2 and 3). The in vitro and in vivo mechanisms of polyphenols are summarized in Tables I and II, respectively.

Figure 3 Classification of phytochemicals, classification of polyphenols into flavonoids and different types of flavonoids.

Table I In vitro studies on the role of polyphenols exerting an immunomodulatory effect on breast cancer cells.

Table I

In vitro studies on the role of polyphenols exerting an immunomodulatory effect on breast cancer cells.

Polyphenol	Phytochemical	Concentration	Experimental models	Activity	Mechanism	Authors, year of publication/(Refs.)
Phenolic acids	Vanillic acid	0.4 mM	SKBR3	↑Type I IFN, ↑M1 macrophages, ↑IFNβ	Stimulation of STING/TBK1/IRF3 pathway	Zhu et al, 2023(52)
	Chlorogenic acid	0.5 mM, 10 mM, 20 mM for 24 h	MDA-MB-231, MDA-MB-453, MCF-10A, 4T1	↑CD4+ T-cells, ↑CD8+ T-cells, ↓NF-κB p65	NF-κB pathway modulation	Zeng et al, 2020(54)
	Caffeic acid (caffeic acid phenethyl ester)	25 mg/ml for 24 and 48 h	LPS-stimulated MDA-MB-231	↓TLR4, ↓NF-κBp65, ↓LC3-II, ↓p62	Inhibition of TLR4 signaling pathway, Autophagy induction	Chang et al, 2017(66)
Stilbenes	Resveratrol	3.12-25 mM for 12 h	4T1, 4T1.2 (subset of 4T1)	↓tBregs, ↓TGF-β, ↑CD8+ T-cells, ↑IFN-γ	Inhibition of tBreg by inactivation of Stat3 phosphorylation and acetylation.	Lee-Chang et al, 2013(62)
	Resveratrol	6.25 mM, 25 mM for 48 h	BCap37, MDA-MB-231, Hs 578T, MCF-7	↑MICA, ↑MICB, ↓c-Myc, ↓miR-17	Promotion of NKG2D recognition causing NK induced death	Pan et al, 2017(67)
	Resveratrol	12.5 mM, 25 mM for 48 h	MDA-MB-231, Bcap37, MCF7, MDA-MB-468	↑ULBP2, ↓MiR-17-5p	NK cell mediated cytotoxicity by activation of MINK1/JNK/c-Jun cascade	Ding et al, 2025(68)
Flavonoids	Apigenin	30 mM for 24 h	MDA-MB-231, MDA-MB-468, SK-BR-3, 4T1	↓PD-L1, ↑IL-2, ↑T-cell proliferation	Inhibition of interferon (IFN)-γ-induced PD-L1 upregulation, Inhibition of STAT1 activation	Coombs et al, 2016(40)
	Hesperidin	0-50 mM for 48 h	MCF-7 and MDA-MB231	↓PD-L1, ↓p-Akt, ↓p-p65, ↓p-ERK	Suppression of NF-κB and Akt pathway activation	Kongtawelert et al, 2020(41)
	Baicalein	10 mM, 20 mM, 40 mM for 7 days	MDA-MB-231, BT459, 4T1+adipocyte co-culture	↓p-STAT3, ↓PD-L1, ↓LEP	Possible downregulation of SREBF1 pathway	Liu et al, 2023(44)
	Taxifolin	5 mM, 10 mM, 50 mM, 100 mM	4T-1	↓HRNR, ↓FLG2, ↓KPRP, ↑CD8+ T-cells	Modulation of breast cancer genes	Lin et al, 2023(55)
	Quercetin	5-120 mM for 24 h	MCF-10A, MCF-10AT, MCF-7, MDA-MB-231	↑IFNγ-R, ↑p-JAK2, ↑p-STAT1, ↓PD-L1, ↑Vδ2 T-cell	Modulation of JAK/STAT1 signaling pathway	Qiu et al, 2021(56)
	Formononetin (bioinformatics analysis)	Bioinformatics study	GSE103512/GSE139038 breast cancer microarray and immune-related gene data	IGF1, ESR1, and CXCL12 have binding sites for formononetin	Inhibition of gene products leading to increase in immune cell infiltration	Song et al, 2022(57)
	Methoxylated quercetin glycoside	1 mM-250 mM for 24-96 h	MDA-MB-231, HR+ BC cells, MCF-7	↑MICA/B, ↑ULBP2, ↑CD155, ↑ICAM-1, ↓TNF-α, ↓IL-10, ↑TP53, ↓MALAT-1 lncRNA, ↑miR-155, ↑miR-146a	Modulation of MALAT-1/miR-155/miR-146a circuit	Abdel-Latif et al, 2022(71)
	EGCG	50-350 mg/ml for 48 h	4T1	↓MDSCs, ↑CD4+ T cells, ↑CD8+ T-cells, ↓pSTAT3, ↓NF-κB p65	Modulation of Arg-1/iNOS/Nox2/NF-κB/STAT3 signaling pathway	Xu et al, 2020(76)
	Naringenin	100 nM for 48 h	MCF10A, MCF7, T47D, BT549, MDA231	↑CD11c+, ↑CD86+, ↑DC	Modulation of FKBP4/NR3C1/NRF2 signaling pathway, pro-DC differentiation and maturation	Xiong et al, 2022(79)
		40 mM for MCF-7, 20 mM for T47D for 48 h	MCF-7, T47D	↑IFI16, ↑IFNβ1, ↑ISG15, ↓DNMT1, ↓DNMT3a, ↓DNMT3b, ↓5mC	Modulation of IFI16 expression	Khan et al, 2022(81)

[i] The upward (↑) and downward (↓) arrows indicate upregulation and downregulation, respectively. TLR, Toll-like receptor; MDSCs, myeloid-derived suppressor cells; MICA/B, major histocompatibility complex class I-related chain A/B; NK, natural killer; NKG2D, natural killer group 2 member D protein; PD-L1, programmed cell death ligand protein 1; HRNR, hornerin; HSP, heat shock protein; FLG2, filaggrin-2; KPRP, keratinocyte proline-rich protein; LPS, lipopolysaccharide; ESR1, estrogen receptor 1; IFI16, interferon-induced protein 16; IFN, interferon; DNMT, DNA methyltransferase.

Table II In vivo studies on the role of polyphenols exerting an immunomodulatory effect on breast cancer cells.

Table II

In vivo studies on the role of polyphenols exerting an immunomodulatory effect on breast cancer cells.

Polyphenol	Phytochemical	Dose range (per day)	Experimental models	Activity	Mechanism	Authors, year of publication/(Refs.)
Phenolic acids	Gallic acid	5 mg/kg for 12 days	4T1 cells in C57BL/6J mice	↓Foxp3+, ↓Foxp3+ PD-L1+ intratumoral Tregs	PD-1 Immune checkpoint modulation	Deng et al, 2022(45)
	Caffeic acid	40 mg/kg, 80 mg/kg for 10 days	Ehrlich ascites tumor (hormone-positive breast cancer) (EAT) in male Swiss albino mice	↑IL-2, ↑IFN-γ, ↑IL-12, ↑M1 macrophages, ↓Arg-1 activity	Increase in M1 level and efficacy, blocking M2 activity	Oršolić et al, 2016(48)
	Caffeic acid	5 mg/kg, 15 mg/kg for 10 days	4T1 cells in female BALB/c mice	↑M1	Not investigated	Xie et al, 2024(49)
	Chlorogenic acid	20 mg/kg, 40 mg/kg every 2 days for 14 days	4T1 in female BALB/c mice	↑CD4+ T cells, ↑CD8+ T cells, ↓NF-κB p65	NF-κB pathway modulation	Zeng et al, 2020(54)
Stilbenes	Piceatannol	10 mg/kg, 20 mg/kg for 30 days	4T1 in female BALB/c mice	↓STAT-3, ↓NFκB p65, ↓M-CSF, ↓MCP-1, ↓M2 macrophages	Inhibition of the activation of NF-κB and STAT3, reduction of MCP-1 and M-CSF	Song et al, 2015(51)
	Resveratrol	20 or 50 mg/mouse every alternate day for 13 days	4T1 and B16F10 bearing Female BALB/c, C57BL/6, and Pmel mice	↓tBregs, ↓TGF-β, ↑CD8+ T cells, ↑IFN-γ	Inhibition of tBreg by inactivation of Stat3 and expression TGFβ	Lee-Chang et al, 2013(62)
	Resveratrol	25 mg/kg, 100 mg/kg for four weeks	BCap37 in female BALB/c (nu/nu) mice, male C57BL/6 mice	↑MICA, ↑MICB, ↓c-Myc, ↓miR-17	Promotion of NKG2D recognition causing NK induced death	Pan et al, 2017(67)
Curcumin	Tetrahydrocurcumin (THC)	80 mg/kg, 1 60 mg/kg for 2 weeks	4T1 cells in Female BALB/c nude mice, BALB/c mice	↓NF-κB, ↓p-IκBa, ↑TNF-a, ↑IL-2. ↑Il-10, ↓PD-L1, ↑CD8+ T, ↓MDSCs, ↑M1	Modulation of CYP1A1/NF-κB/PD-L1 axis	Zeng et al, 2023(42)
	Curcumin	40 mg/kg, 80 mg/kg for 35 days	4T1 cells in female BALB/c mice	↑STAT4, ↑IL-12, ↓STAT3, ↓IL-10, ↓Arg-1, ↑M1, ↓M2	Modulation of M1/M2 balance	Shiri et al, 2015(83)
Flavonoids	Baicalein	50 mg/kg every other day for 2 weeks	4T1 in female Balb/c mice	↑M1, ↑IRF1, ↑KYNU, ↑CD86, ↑IL-1β, ↑TNF-α, ↑CXCL9/CXCL10, ↓PI3Kγ	Modulation of NF-κB/TNF-α signaling. pathway	He et al, 2021(50)
	Naringenin	100 mg/kg for 24 days	4T1 in female BALB/c mice and C57BL/6 mice	↑IFN-γ,↑ IL-2, ↑CD44highCD62L−T cells, ↓TGF-β1, ↓IL-10, ↓Treg	Inhibition of TGF-β production	Qin et al, 2011(59)
	Apigenin	25 mg/kg, 50 mg/kg, 100 mg/kg for 21 days	4T1 cells in female BALB/c mice	↓Tregs	Modulation of PI3K/AKT/NF-κB pathway	Zhang et al, 2024(63)
	EGCG	250 mg/ml, 500 mg/ml, 1000 mg/ml, 2000 mg/ml pre-treatment for 1 month.	4T1 in male BALB/c mice	↓MDSCs, ↑CD4+ T cells, ↑CD8+ T cells, ↓pSTAT3, ↓NF-κB p65	Modulation of Arg-1/iNOS/Nox2/NF-κB/STAT3 signaling pathway	Xu et al, 2020(76)
	Quercetin + doxorubicin	2 mg/mice quercetin daily, 5 mg/kg doxorubicin injections/week	4T1 in female BALB/c and athymic nude mice	↑IFN-γ, ↑IL-2, ↓IL-4, ↓IL-10	Regulation of Th1/Th2 cytokines	Du et al, 2010(58)
	Taxifolin	50 mg/kg twice/week for 25 days	4T-1 in BALB/CJ mice	↓HRNR, ↓FLG2, ↓KPRP, ↑CD8+ T	Modulation of breast cancer genes	Lin et al, 2023(55)
	Genistein	500 ppm genistein-lifelong, pre-pubertal, adult, and post-diagnosis	Female Sprague-Dawley rats, cancer induced by DMBA	↓Foxp3, ↑Cd8a, ↓IL-6	Inhibition of IL-6 expression	Zhang et al, 2017(46)
	Genistein + tamoxifen	340 ppm tamoxifen + 500 ppm genistein (diet), initiated at 11-13 mm tumors; combination for 9 weeks, genistein alone extended 10 weeks post tamoxifen	Female Sprague-Dawley rats, ER+ mammary tumor	↑Cd8a, ↓Foxp3, ↓Tgfβ1, ↓Pd1, ↓Ctla-4, ↓IL-6 in tamoxifen sensitive tumors	PD-1/CTLA-4 checkpoint inhibition with suppression of the TGF-β/IL-6 immunosuppressive axis.	Andrade et al, 2021(47)

[i] The upward (↑) and downward (↓) arrows indicate upregulation and downregulation, respectively. M-CSF, macrophage colony-stimulating factor; MCP-1, monocyte chemoattractant protein 1; NK cell, natural killer cell; NKG2D, natural killer group 2 member D protein; PD-L1, programmed cell death ligand protein 1; MDSCs, myeloid-derived suppressor cells.

For ease of understanding, the immunomodulatory effects of polyphenols have been classified into the following sub-categories as adapted by de Carvalho et al (9): i) Role of polyphenols in modulating immune checkpoints; ii) role of polyphenols in modulating TAMs and M1/M2 polarization; iii) role of polyphenols in regulating T-cell-mediated immunity; iv) role of polyphenols in modulating Toll-like receptors (TLRs); v) role of polyphenols in upregulating NK cell activity; vi) role of polyphenols in suppressing MDSCs; vii) role of polyphenols in regulating DC activity; and viii) role of polyphenols in mediating the activity of inflammasomes.

Polyphenols modulate immune checkpoints. An increasing amount of evidence indicates that polyphenols are involved in the modulation of immune checkpoint pathways, such as PD-1/PD-L1 signaling (Fig. 4). However, the magnitude and consistency of these effects are variable and dependent on compound class, dosage and experimental conditions. For example, flavonoids such as apigenin and hesperidin demonstrate direct effects on tumor cells by suppressing PD-1/PD-L1 expression. It has been demonstrated that apigenin (at 30 µM) consistently suppresses interferon (IFN)-γ-induced PD-L1 expression across multiple BC cell lines via the inhibition of STAT1, while also enhancing IL-2 production and T-cell proliferation, indicating both checkpoint inhibition and immune activation (40) as shown in Table I. By comparison, hesperidin (at 10-50 µM) exhibits a broader, yet less functionally validated mechanism by targeting the NF-κB, AKT and ERK signaling pathways to reduce PD-L1 expression. In addition, its effect is restricted to fewer cell models, limiting its translational relevance (41) Similarly, tetrahydrocurcumin (THC) also exerts a comprehensive effect, reducing not only PD-L1, but also simultaneously modulating MDSCs, macrophage polarization, and CD8+ T-cell infiltration via the NF-κB axis. While these effects occur at relatively high doses (80-160 mg/kg) in 4T1 cells in mouse models, raising concerns about translational feasibility (42), a reported safe intake level of 2 mg/kg per day suggests a significant gap between experimental and clinically acceptable dosing (43).

Figure 4 Illustration depicting the modulation of immune checkpoints, such as PD-1, PD-L1 and CTL4 by polyphenols such as genistein, caffeic acid, resveratrol, chrysin, etc. PD-1, programmed cell death protein 1; PD-L1, programmed cell death ligand protein 1; CTLA-4, cytotoxic T-lymphocyte antigen-4; IL, interleukin.

Baicalein has also been found to reduce PD-L1 expression in MDA-MB-231, BT549 and 4T1-adipocyte co-culture cell models, accompanied by decreased levels of p-STAT3 and leptin. Baicalein appears to interfere with adipocyte-associated tumor microenvironment signaling, possibly via the downregulation of the sterol regulatory element-binding transcription factor 1 pathway. This suggests that baicalein may be particularly relevant in obesity-associated BC, where adipocyte-derived leptin can enhance immune escape (44) as shown in Table I.

In a previous study, gallic acid (5 mg/kg, 12 days) demonstrated a targeted in vivo effect in 4T1 tumor-bearing mice, where it reduced both Foxp3+ and PD-L1+Foxp3+ intra-tumoral Treg populations (45), as shown in Table II. This suggests that gallic acid may play a dual checkpoint-modulating and Treg-destabilizing role by acting upstream at the level of immune suppression rather than directly on tumor PD-L1 expression. However, compared to flavonoids, its action appears narrower, with limited engagement of broader signaling pathways (45). The action of genistein is mostly context-dependent (46,47). At 500 ppm, it reduces Foxp3 and IL-6, while increasing CD8a levels, suggesting enhanced cytotoxic responses. Unlike apigenin and hesperidin, genistein modulates upstream inflammatory cytokines that indirectly influence immune checkpoint pathways. These effects become more evident in its combination with tamoxifen, where reductions in PD-1 and CTLA-4 are observed only in responsive tumors in mouse models highlighting it's dependence on tumor context. This context-dependent variability of genistein may reduce its reliability as a standalone checkpoint modulator (46,47).

Polyphenols play a role in the modulation of M1/M2 polarization. Polyphenols have also demonstrated their potential in regulating TAMs and shifting macrophage polarization towards the anti-tumorigenic M1 phenotype, although the mechanisms and extent of activity vary between compounds (Fig. 5). Caffeic acid exhibits broad immunomodulatory activity at high concentrations (40-80 mg/kg) by increasing the levels of IL-2, IFN-γ, IL-12 and M1 macrophages, while reducing arginase-1 activity, indicating the suppression of the M2 phenotype. Its reactive oxygen species (ROS)-inhibitory properties may further contribute to reduced TAM formation and angiogenesis (48). Notably, another study on caffeic acid produced similar M1-promoting effects at lower concentrations (5-15 mg/kg), in 4T1 cells in female BALB mice as shown in Table II, although its mechanism of action was not investigated (49). This may be due to differences in tumor models used and the end points investigated in that study.

Figure 5 Illustration of the modulation of M1/M2 polarization by polyphenols in breast cancer. IFN, interferon; MCP-1, monocyte chemoattractant protein 1; M-CSF, macrophage colony-stimulating factor; ROS, reactive oxygen species; IL, interleukin.

Similarly, the in vivo administration of baicalein also reprograms TAMs towards the M1 phenotype by increasing the levels of M1-associated markers, such as TNF-α, IL-1β, CXCL9 and CXCL10, while suppressing PI3Kγ signaling (50) as shown in Table II. Piceatannol, however, acts more indirectly on 4T1 cells in mice by reducing macrophage colony stimulating factor and monocyte chemoattractant protein expression, thereby lowering TAM infiltration and relatively favoring M1 macrophages without strongly inducing pro-inflammatory cytokines (51) as depicted in Table II.

A previous study on the effect of vanillic acid on macrophages in breast tumor microenvironment (TME) by Zhu et al (52) revealed that vanillic acid promotes M1 polarization by increasing the production of type I IFN through the activation of the STING/TBK1/IRF3 pathway in macrophages. Unlike other polyphenols that mainly suppress tumor-promoting pathways, vanillic acid appears to stimulate innate immune signaling directly. However, evidence remains limited to a small number of experimental models (52).

Polyphenols promote the activation of T-cell-mediated immunity. T-lymphocytes are necessary for the cell-mediated immune response of the host to cancers; modern tumor immunotherapy aims to stimulate or boost T-cell responsiveness to antigens. It has been discovered that polyphenols alter the activity of various T-cell subsets, including Tregs, T-Helper (TH) cells and CTLs (53).

Polyphenols and CTLs. Several polyphenols, including epigallocatechin gallate (EGCG), genistein and resveratrol, have been shown to increase the CTL count and activity (9). Chlorogenic acid has been shown to improve antitumor immunity by suppressing the NF-κB/EMT signaling pathway and increasing CD4+ and CD8+ T-cell populations of 4T1 in female BALB mice (54), as depicted in Table II. Similarly, taxifolin has also been shown to promote CD8+ T-cell infiltration and to suppress tumor progression, although its effects appear to be mediated indirectly through the modulation of BC-associated genes, such as Hornerin (HRNR), (Filaggrin-2) FLG2 and keratinocyte proline-rich protein (KPRP) rather than through classical cytokine signaling pathways (55) as shown in Table I. In another study, quercetin demonstrated a comparatively stronger and direct immunomodulatory effect (56). The administration of quercetin not only suppressed PD-L1 expression through JAK/STAT1 signaling, but also directly promoted the proliferation of immunomodulatory γδ T-cells, which helps in eliminating tumor cells and regulating the immune system (56) as shown in Table I. Compared to chlorogenic acid and taxifolin, quercetin therefore appears to exert both checkpoint-regulatory and CTL-activating effects simultaneously. By contrast, the findings on formononetin remain limited to computational predictions without experimental validation, although, it has been observed that formononetin is able to bind to three different immune-related genes, such as insulin-like growth factor (IGF1), estrogen receptor 1 (ESR1), and CXCL12 in a stable manner, leading to an increase in the CD8+ T-cells and CD4+ T-immune cells infiltration, as demonstrated by TIMER2.0 database analysis (57).

Polyphenols modulate TH cells. Polyphenols also regulate TH cell-associated cytokines, particularly by shifting immunity toward a Th1 phenotype. A previous study demonstrated that quercetin combined with doxorubicin increased IFN-γ and IL-2 levels, while reducing IL-4 and IL-10 in a mouse model (58), as shown in Table II. This thereby promoted a Th1-dominant immune response and reversed doxorubicin resistance associated with low CD8+ and CD4+ T-cell infiltration (58). This shift toward Th1 immunity likely contributed to improved CTL activation and the reversal of chemoresistance. In another study, naringenin indirectly produced similar Th-1 skewing effects in a mouse model, by increasing IFN-γ and IL-2 levels, while reducing TGF-β1 and IL-10(59), as shown in Table II. Compared to quercetin, naringenin exhibited broader immunoregulatory effects by simultaneously improving survival and reducing metastasis despite showing limited direct anti-proliferative activity, suggesting that immune modulation itself contributed significantly to therapeutic benefit (59). However, these immunomodulatory effects were observed with orally administered narigenin at a higher dose (100 mg/kg), probably due to poor bioavailability (60). Nevertheless, clinical research has reported that oral doses of 150-900 mg naringenin are safe and tolerated in humans, suggesting that suitable therapeutic outcomes may be achieved at clinically feasible doses (61).

Role of polyphenols in modulating the levels of Tregs. Several polyphenols have demonstrated the ability to suppress Tregs, which are major contributors to immune evasion in BC. The in vitro and in vivo study conducted by Lee-Chang et al (62) on BC cell lines revealed that resveratrol administered at sub-lethal doses had an immunomodulatory effect where it favorably inhibited tBregs and STAT3, which caused a subsequent decline of Foxp3+ Tregs in a TGF-β-dependent manner, as shown in Table II. While the activity of resveratrol enhanced the immune function, by blocking tBregs, it also prevented metastasis of BC cells to the lungs (62). Correspondingly, in another study, apigenin reduced Treg populations through the modulation of the PI3K/AKT/NF-κB pathway in a mouse model (63), as shown in Table II. Unlike resveratrol, which primarily targeted Treg-inducing B-cells and STAT3 signaling, apigenin appeared to directly interfere with inflammatory pathways involved in Treg maintenance (63). Additionally, naringenin was also reported to suppress TGF-β1-induced Treg production, suggesting overlap between restoration of Th1 immunity and inhibition of immunosuppressive Treg activity (59).

Role of polyphenols in modulating TLRs. Toll-like receptors or TLRs play a vital role in mediating innate immune response in the host (64). Of special interest is TLR-4, which is expressed in the plasma membrane of host immune cells and cancer cells and can recognize lipopolysaccharide (LPS). TLR-4 is known to be overexpressed in a plethora of cancers including BC; its activation is associated with a poor prognosis attributed to extensive proliferation and invasion (65). A previous study demonstrated that caffeic acid phenethyl ester (CAPE) in LPS-stimulated MDA-MB-231 cells suppressed TLR-4 and NF-κB p65 signaling and modulated the autophagy markers, LC3-II and p62, indicating that CAPE may regulate macrophage-associated inflammatory signaling through both TLR-4 inhibition and autophagy induction (66). Compared to other polyphenols discussed above, CAPE appears to target an upstream innate immune receptor rather than directly modulating immune components. While this renders the mechanism distinct, it is limited only to LPS stimulated models, reducing confidence in broader applicability. Moreover, whether CAPE induced autophagy is a consequence of TLR-4 inhibition or an independent parallel mechanism remains unclear and needs to be further explored (Fig. 6).

Figure 6 Illustration depicting the role of polyphenols in the modulation of TLRs. TLR, Toll-like receptor; LPS, lipopolysaccharide.

Role of polyphenols in upregulating NK cell activity. As NK cells are the first line of defense against tumor processes, investigating the mechanisms through which polyphenols regulate NK cells may lead to the development of novel therapeutic approaches. Among the compounds studied, resveratrol has demonstrated one of the most extensively characterized effects. As previously demonstrated, in BC cells, resveratrol upregulated the expression of major histocompatibility complex class I-related chain A/B (MICA/B), key activators of NK cells by modulating a novel c-Myc/miR-17 pathway by suppressing the expression of the miR-17 gene (67). Notably, similar effects were reproduced in vivo at 25 and 100 mg/kg, suggesting consistency across experimental systems (67) as shown in Table II. Another in vivo study on MDA-MB-231 tumor-bearing mice demonstrated that resveratrol (at 25-100 mg/kg) increased UL16 binding protein 2 expression, while downregulating miR-17-5p expression, thereby promoting NK cell-mediated cytotoxicity through activation of the MINK1/JNK/c-Jun cascade (68). However, the effects of resveratrol are biphasic; low concentrations (3.13 to 1.56 µM) have been shown to enhance NK cell cytotoxicity, whereas higher concentrations (50 µM) promote NK cell apoptosis (69). This is a key consideration for clinical translation as the activity of resveratrol contrasts with that of other polyphenols, where a higher concentration usually corresponds to a more potent antitumor effect.

Wang et al (70) demonstrated that exercise, along with the administration of daidzein in tumor-bearing mice synergistically led to a reduction in tumor size and proliferation, as compared to the control mice. This may be due to the increased production and mobilization of NK cells. This was supported by an increase in the levels of IL-6 and epinephrine in the plasma. NK cells are also known to initiate FasL-mediated cytotoxicity towards cancer cells; this was evidenced by an increase in the levels of Fas and Fas-associated death domain (FADD) proteins (70). The subsequent increase in Fas/FADD mediated apoptosis led to an increase in tumor suppression, instigating the effectiveness of daidzein combined with exercise. Compared to resveratrol, the effects of daidzein were less tumor-cell-specific and appeared to be dependent on systemic physiological changes induced by exercise. This makes it difficult to distinguish whether the antitumor effects arise primarily from the polyphenol itself or from the exercise-induced immune response (70).

Additionally, Abdel-Latef et al (71) reported that methoxylated quercetin glycoside (MQG) significantly improved NK cell cytotoxicity in multiple BC cell lines by increasing the expression of MICA/B and CD155 via the MALAT-1/miR-155/miR-146a axis. The levels of cytokines, such as IL-10, which inhibit NK cell responses, were also significantly downregulated in the BC cell line (71). Compared to resveratrol, which primarily targets NKG2D ligand induction, MQG appears to influence a wider network of NK recognition molecules, suggesting potentially stronger sensitization of tumor cells to NK-mediated killing. However, the evidence remains limited to in vitro systems, and no in vivo validation has yet been reported, at least to the best of our knowledge.

Role of polyphenols in suppressing MDSCs. MDSCs are a diverse group of cells characterized by their myeloid origin, immature state and potency in suppressing T-cell responses. They are found in unusually high levels in cancer, and their expression is associated with a poor prognosis (72). Polyphenols have shown promise in modulating MDSC activity and numbers (73). Forghani et al (74) discovered that silibinin reduced MDSC levels in tumors, the spleen and peripheral blood in tumor-bearing mice. This resulted in a reduction in tumor volume (74). MDSCs are known to express a high level of PD-L1, which can cause the diminution of T-cell activity by interacting with PD-1 on T-cells (75). Among the reported compounds, silibinin was one of the earliest polyphenols shown to suppress MDSCs. In both in vivo and in vitro BC models, EGCG administration has led to a significant reduction in the number of MDSCs and increased CD4+ and CD8+ T-cell infiltration. Xu et al (76) proposed and confirmed that EGCG targets MDSCs through the Arg-1/iNOS/Nox2/NF-κB/STAT3 signaling pathway. However, its limitation lies in the concentration range (250-2,000 µg/ml) and the lack of standardized body weight-adjusted dose used for EGCG. A human clinical study observed that EGCG intake up to 338 mg/day as a solid bolus and up to 704 mg/day in beverage form is generally considered safe (77). The absence of body weight-adjusted dosing in that study limits direct translational comparison.

Role of polyphenols in regulating DC activity. DCs are crucial APCs that bridge innate and adaptive immunity by cross-presenting tumor-associated antigens to naive T-cells, thereby initiating specific antitumor effector responses (78). Despite their importance in BC immunology, evidence for the direct modulation of DCs by polyphenols remains extremely limited, with naringenin being one of the few compounds investigated in this context. Xiong et al (79) demonstrated that naringenin at a relatively low concentration (100 nM for 48 h) suppressed the proliferation of BC cells by inhibiting NRF2-dependent tumorigenesis via the FKBP4/NR3C1 axis. This pathway promoted DC differentiation and maturation, potentiating T-cell-mediated anti-tumor response (79). While the effective concentration of 100 nM is notably lower than the micromolar or mg/kg doses reported for many other polyphenols, their study was limited to in vitro systems and functional assays evaluating antigen presentation efficiency or downstream T-cell priming were not extensively assessed (79).

Role of polyphenols in mediating the activity of inflammasomes. Inflammasomes are intracellular multiprotein complexes that regulate innate immune responses by sensing pathogen and damage associated signals and triggering inflammatory cytokine release. When activated within the TME, they are involved in the modulation of cytokine secretion, immune cell recruitment and T-cell differentiation (80). Among the polyphenols investigated, Khan et al (81) examined the effects of EGCG on the inflammasome component IFN-induced protein 16 (IFI16). In vitro and molecular docking analyses revealed that EGCG upregulated the expression of IFI16 and its downstream transcription target IFNβ1 in the MCF-7 BC cell line (81). In silico molecular docking analyses revealed that EGCG is a potent DNA methyltransferase inhibitor; this was supported by in vitro analyses that demonstrated that EGCG decreased the expression of various DNA methyltransferases, which led to a consequent decrease in the 5mC level, leading to IFI16 gene re-expression (81) as depicted in Table I. This indicates that EGCG may regulate inflammasome-associated responses indirectly through epigenetic reprogramming, rather than by directly targeting classical inflammasome components such as NOD-like receptor family pyrin domain containing 3 (NLRP3) or apoptosis-associated speck-like protein containing a CARD (ASC).

5. Improving polyphenol bioavailability through nanoparticle-based delivery systems

The therapeutic potential of polyphenols is influenced by their metabolism and limited bioavailability. In the intestinal mucosa and internal tissues, polyphenols are converted to glucuronide, sulphate and methyl groups following absorption. The amounts of non-conjugated polyphenols in plasma are minimal. Recent developments in nanotechnology have provided promising solutions to these issues. Polyphenols can be made more soluble, stable and bio-distributable by encasing them in nanoparticles, increasing the anticancer activity and immunomodulatory properties (82).

In the context of the present review, nanoformulations may preserve or even enhance the immunomodulatory effects of the parent polyphenol. For example, in a previous study, dendrosomal curcumin reduced tumor growth in 4T1 tumor-bearing mice by shifting the macrophage polarization from M2 to M1(83). This was supported by an increase in the levels of STAT4 and IL-12, suggesting an increase in the levels of M1, and a decrease in the levels of STAT3, IL-10 and arginase I gene expression, suggesting a decline in the M2 level (83). Similarly, in another study, baicalein-loaded methoxy polyethylene glycol-poly (lactic-co-glycolic acid nanoparticles modulated the M1/M2 balance both in vitro and in vivo (84). Youssry et al (85) investigated the effects of curcumin nano-emulsion on inflammasome-related pathways using peripheral blood mononuclear cells from patients with BC. The treatment increased the levels of the inflammasome adaptor protein, ASC, with a subsequent decrease in the levels of IL-1B, IL-18 and Bcl6. Although ASC is often upregulated in tumors, that study suggested that curcumin nano-emulsion may inhibit ASC from binding to NLRP3, thereby disrupting inflammasome components (85). Additionally, curcumin nano-emulsion was also found to decrease the levels of the immune marker, CD163, which may play a role in reducing M2 macrophages (85). These findings are critical, as they extend nanoparticle benefits beyond enhanced cytotoxicity to direct remodeling of the tumor immune microenvironment.

A number of other polyphenol-based nanoparticles, including formulations of vanillic acid, veratric acid, caffeic acid and piceatannol, have also been investigated in BC models and have generally demonstrated improved solubility, sustained release and enhanced anticancer efficacy compared to their free forms (86-89). However, most of these studies focus primarily on tumor suppression and apoptosis, rather than specifically evaluating immunomodulatory outcomes. Recent approaches, such as multifunctional nanoplatforms and metal-phenolic networks (MPNs) also show promise. MPNs utilize the synergy between metal ions and polyphenol ligands to enable controlled drug delivery and enhance tumor immune modulation, presenting a novel direction in cancer nanomedicine (73). The recent review by Zhang et al (90) provides a detailed overview of natural compound-based nanoparticle systems developed between 2018 and 2025 and may serve as a useful reference for future studies exploring newer polyphenol nanoformulations in BC.

6. Future perspectives

Polyphenol combination therapies that target the immune system. Recent studies have suggested that the future of polyphenol-based immunotherapy in BC lies in combination modalities that simultaneously improve delivery and reprogram the TME (91). Multiple studies have revealed a clear trend: Free polyphenols often exert modest effects, whereas nanoformulations or combination treatments produce stronger end-results (90). A highly relevant study on salvianolic acid B-based FeSH nanosystem integrated photothermal therapy with anti-PD-L1 blockade, that effectively converted immunologically ‘cold’ TNBC tumors into ‘hot’ tumors by inducing immunogenic cell death, suppressing TGF-β-mediated immunosuppression and upregulating PD-L1(92). This is more mechanistically targeted than the resveratrol-curcumin-quercetin formulation, which primarily shifted immune cell composition by increasing T-cell infiltration, while suppressing M2 macrophages, Th2 cells and N2 neutrophils (93). While both approaches reversed immunosuppression, the salvianolic acid B-FeSH nanosysten directly integrated checkpoint immunotherapy, aligning itself for future translation.

Another major treatment path is combining polyphenols with external energy-based therapies, as for as photothermal, sonodynamic or radiotherapy. The nano-encapsulated polyphenols not only take advantage of the enhanced permeability and retention effect (94), but also absorbs external energy to actively exploit tumor-specific stimuli for controlled release and immune activation. For example, naringenin-loaded photothermal bovine serum albumin-biomineralized manganese dioxide nanoparticles combined with photothermal treatment enhanced antitumor immunity and reduced metastatic potential in TNBC, while resveratrol-chitosan nanoparticles improved radiosensitivity and restored immune markers such as IFN-γ and STAT3 (95,96). More recently, ROS-responsive resveratrol nano agents used in sonodynamic therapy introduced a highly complex mechanism by inducing suprathreshold autophagy and immunogenic cell death, which may overcome the transient immune activation seen with simpler formulations (97). However, most of these systems remain restricted to murine TNBC models; thus, it is difficult to determine whether similar immune remodeling would occur in hormone receptor-positive or HER2-positive BCs. Additionally, direct comparisons with free polyphenol controls are often lacking in some combination and nanoparticle studies, rendering it difficult to separate treatment effects from improved pharmacokinetics (98). These studies would highly benefit from standardized experimental frameworks, which would allow head-to-head comparison between different treatment regimens.

Precision medicine. The highly heterogenous nature of BC warrants specificity in treatment strategies, particularly the highly immunogenic HER2-positive BC and TNBC subtypes. Such treatments should not only rely on targeting the cancer cells, but also the TME components. The anticancer effects of polyphenols are often pleiotropic and non-specific (99). For example, the variable immunological effects of genistein across tamoxifen-sensitive, resistant, and recurrent tumors underscore the need for precision-guided application of polyphenols, as their efficacy may be highly dependent on tumor phenotype and therapeutic context (47). The immunomodulatory specificity of polyphenols can be improved according to the primary treatment modality, as different compounds appear to preferentially enhance the efficacy of immunotherapy, chemotherapy, radiotherapy, or immunogenic stress-based therapies. Dose- and formulation-dependent variability further complicates clinical translation; standardized dose optimization remains essential to distinguish true immunomodulatory effects from nonspecific cytotoxicity (100).

Future studies are thus warranted to prioritize precision-guided combination strategies, where polyphenols are paired with immunotherapies based on tumor subtype, immune phenotype, and polyphenol-conventional modality compatibility rather than using generalized formulations. Next-generation sequencing and artificial intelligence have become vital tools that can identify new molecular targets, optimize and personalize treatment strategies, and predict patient responses to polyphenol-based immunotherapy (101).

7. Conclusions

The advent of immunotherapy has marked a new milestone for the treatment of BC, with ICIs, cancer vaccines and monoclonal antibodies expanding treatment options to previously constrained alternatives. While immunotherapies are improving constantly, their success is marred by toxicity and resistance. The review by Golonko et al (102) poses a critical question: ‘to what extent can boosting the immune system advance anticancer therapy?’

However, the untapped realm of personalized immunotherapies provides promising possibilities for the clinical translation of polyphenol-based strategies; however, substantial work is required to identify reliable biomarkers, optimize dosing, and validate efficacy across distinct BC subtypes. While limited clinical trials (clinicaltrials.gov database) (ID NCT05724329, NCT07248020) have been registered to investigate into polyphenol-based immunotherapies in different types of cancer, to the best of our knowledge, there are still no clinical studies available on the effects of polyphenols on the immune landscape of BC. Even though translational limitations persist, the presence of such clinical trials indicates a growing recognition of polyphenols as therapeutically relevant in cancer immunotherapy. The path from plant-derived metabolites to clinically relevant immunotherapeutic adjuncts remains complex, yet each preclinical advancement highlights the untapped capacity of natural compounds to shape the future of personalized cancer care.

Acknowledgements

The authors are grateful to Dr Sudhindra Shamanna, Academic President, Manipal Academy of Higher Education, Dubai, UAE, for his constant support and encouragement.

Funding

Funding: No funding was received.

Availability of data and materials

Not applicable.

Authors' contributions

RR and AH were involved in the design of the study. RR, LD and AS contributed towards the literature search for relevant references. RR and LD wrote the manuscript. RB edited the manuscript. All authors have read and approved the final manuscript. Data authentication is not applicable.

Ethics approval and consent to participate

Not applicable.

Patient consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

References