Advancing human epidermal growth factor receptor 2-positive gastric cancer therapy: Toward targeted immunotherapy and antibody-drug conjugates

Table 1 Overview of traditional human epidermal growth factor receptor 2-positive gastric cancer treatment strategies

Therapeutic category	Regimen/agents	Mechanism of action	Limitations and challenges	Key clinical evidence
Traditional chemotherapy	Fluorouracil + platinum/taxanes	Interferes with DNA synthesis or cell division	Limited survival benefit; low response rates; short duration of response; lack of specificity; significant adverse effects	Multiple phase III trials
Trastuzumab + chemotherapy	Trastuzumab + chemotherapy (various combinations)	Blocks HER2 signaling; mediates ADCC; suppresses angiogenesis	Enhanced benefit in HER2-high; limited efficacy in HER2-low; primary/acquired resistance; HER2 heterogeneity affects efficacy; first-line: Median OS plateaued at 13-16 months; lack of breakthrough improvements; limited survival benefit PFS; second-line: Cross-line trastuzumab failed to improve PFS; lack of HER2 stratification; most patients eventually develop resistance	TOGA[11,14-16,32,33,37,38]
Other HER2-targeted agents	Pertuzumab	Forms dual blockade with trastuzumab	Failed primary endpoints in GC phase III; divergent responses between GC and breast cancer	JOSHUA, MARIANNE[40]
	Small-molecule TKIs	Inhibits HER2 intracellular tyrosine kinase activity	Lapatinib improved ORR but not OS; lapatinib + trastuzumab not superior to monotherapy; different HER2 expression patterns; more complex signaling pathways; unique tumor microenvironment	TYTAN, BO15970[32,38,40,41]

HER2: Human epidermal growth factor receptor 2; TKI: Tyrosine kinase inhibitor; ADCC: Antibody-dependent cellular cytotoxicity; OS: Overall survival; PFS: Progression-free survival; GC: Gastric cancer; ORR: Objective response rate.

Table 2 Overview of combination strategies for human epidermal growth factor receptor 2-positive gastric cancer

Therapeutic category	Regimen/agents	Mechanism of action	Key clinical trials/evidence	Ref.
Targeted + immunotherapy + chemotherapy triplet regimens	Pembrolizumab + trastuzumab + chemotherapy	Pembrolizumab: PD-1 inhibitor, reverses T-cell exhaustion; trastuzumab: Blocks HER2 signaling and induces ADCC; chemotherapy: Induces immunogenic cell death, enhancing tumor antigen presentation	KEYNOTE-811 (phase III): Became the new first-line standard for advanced HER2-positive GC/GEJA, demonstrating superior PFS and OS (median OS: 20.0 months vs 16.8 months)	Ding et al[17]; Wang et al[48]; Cheng et al[49]; Yamashita et al[51]; Li et al[55]; Zhu et al[56]; Yu et al[57]; Yi et al[58]
	Atezolizumab + trastuzumab + XELOX	Atezolizumab: PD-L1 inhibitor, enhances antitumor immunity; trastuzumab and chemotherapy: Provides direct HER2 blockade and tumor cell killing	A phase II randomized trial: In the perioperative setting for locally advanced resectable GC, significantly improved pathologic complete response rate (38% vs 14%)	Peng et al[1]
ADCs	Trastuzumab deruxtecan	HER2-targeted ADC with a topoisomerase I inhibitor payload and a cleavable linker, enabling a potent “bystander killing effect” against heterogeneous tumors	DESTINY-gastric series: DG-04 (phase III): Redefined 2nd-line standard (median OS: 14.7 months vs 11.4 months). DG-01 (phase II): Robust activity in later-line (ORR = 51.3%). DG-03/05: Evaluating 1st-line combinations	Shitara et al[46]; Oaknin et al[59]; Aoki et al[60]; Chen et al[61]; Janjigian et al[62]; Janjigian et al[63]; Shitara et al[64]; Shitara et al[65]; Yamaguchi et al[66]; Peng et al[67]
	Disitamab vedotin	HER2-targeted ADC with the microtubule inhibitor MMAE, enabling precise cytotoxicity and efficacy in HER2-low expressions	Phase I/II trials: Showed promising efficacy in heavily pretreated patients with HER2-overexpressing and HER2-low GC	Chen et al[61]; Xu et al[69]; Peng et al[70]
	Ado-trastuzumab emtansine	HER2-targeted ADC with the maytansinoid payload DM1, utilizing a stable, non-cleavable linker	Phase III trials (e.g., GATSBY): Failed to demonstrate superior survival benefit over standard chemotherapy in GC, limiting its clinical application	Pegram et al[45]; Barfield et al[71]
Investigational ADC agents	A166	A site-specifically conjugated ADC with a uniform drug-antibody ratio (approximately 4), delivering the potent microtubule inhibitor duostatin-5	Early-phase I trials: Showed preliminary antitumor activity in HER2-positive solid tumors (including GC), primarily in breast cancer models to date	Zhang et al[20]; Hu et al[73]; Liu et al[74]; Hu et al[75]
	LCB-ADC	A novel ADC with an optimized cleavable linker and MMAF payload, designed for enhanced tumor-specific payload release and a wider therapeutic window	Preclinical studies: Demonstrated superior potency and efficacy in HER2-high and ado-trastuzumab emtansine-resistant patient-derived xenograft models	Shin et al[21]; Díaz-Rodríguez et al[68]; You et al[72]

ADC: Antibody-drug conjugate; PD-1: Programmed cell death 1; HER2: Human epidermal growth factor receptor 2; PD-L1: Programmed cell death ligand 1; ADCC: Antibody-dependent cellular cytotoxicity; MMAF: Monomethyl auristatin F; MMAE: Monomethyl auristatin E; GEJA: Gastroesophageal junction adenocarcinoma; GC: Gastric cancer; OS: Overall survival; PFS: Progression-free survival; ORR: Objective response rate.

Table 3 Overview of novel therapeutic modalities for human epidermal growth factor receptor 2-positive gastric cancer

Therapeutic category	Regimen/agents	Mechanism of action	Current limitations/challenges	Ref.
Bispecific antibodies	PRS-343	Targets HER2 and 4-1BB, promoting T-cell proliferation and cytokine production via HER2-dependent 4-1BB clustering	Preclinical stage; clinical validation needed for potential risks like CRS	Hinner et al[78]
	IBI315	Concurrently blocks PD-1 and HER2 signaling, establishing a self-reinforcing immunostimulatory cycle via gasdermin B-mediated pyroptosis	Efficacy and safety need confirmation in large-scale clinical trials	Lin et al[79]
	KN026	Recognizes two distinct HER2 domains, achieving potent dual HER2 signal blockade	Optimal combination regimens and long-term benefits need exploration, despite promising ORR (56%)	Ji et al[80]
	CD40 × HER2	Activates CD40 signaling to repolarize macrophages towards the M1 antitumor phenotype, reversing C-C motif chemokine ligand-driven resistance	Preclinical stage; long-term in vivo safety and efficacy require evaluation	Sun et al[82]
	IMM2902	Targets CD47 and HER2, stimulates macrophages to recruit T and NK cells via CXCL9/CXCL10	Clinical potential awaits validation in human trials	Zhang et al[83]
CAR-T cell therapy	HER2 CAR-T	Genetically engineered T cells express HER2-specific CARs for targeted tumor cell elimination	Immunosuppressive TME; risk of on-target/off-tumor toxicity; cytokine release syndrome and neurotoxicity; antigen heterogeneity	Budi et al[85]; Xu et al[86]; Qi et al[88]; Simon et al[89]; Guzman et al[90]
	ARC-T cells	Achieves selective tumor cell killing while minimizing off-tissue toxicity through spar X affinity and dose modulation	Early development stage; clinical translation potential needs validation	Mu et al[91]
Targeted thorium conjugates	HER2-TTC	Delivers the alpha-particle emitter thorium-227 to HER2+ cells, inducing potent, localized DNA double-strand breaks	Efficacy depends on sustained HER2 expression; limited clinical data (trial No. NCT04147819 ongoing); long-term safety requires evaluation	Pernas et al[35]; Wickstroem et al[92]; Karlsson[93]; Garg et al[94]; Anderson et al[95]

CAR-T: Chimeric antigen receptor T-cell immunotherapy; HER2: Human epidermal growth factor receptor 2; CD: Cluster of differentiation; ARC: Acrobatic recombinase cassette; TTC: Targeted thorium conjugate; CCL: C-C motif chemokine ligand; PD-1: Programmed cell death 1; NK: Natural killer; CRS: Cytokine release syndrome; ORR: Objective response rate; TME: Tumor microenvironment.

Table 4 Overview of resistance mechanisms to human epidermal growth factor receptor 2-targeted therapy and corresponding strategies

Resistance mechanism	Key molecular events and evidence	Consequences	Potential overcoming strategies	Ref.
HER2 gene mutations and structural alterations	Antibody-mediated drug resistance. L755S mutation: Mediates acquired resistance to TKIs. p95HER2 truncation: Lacks the extracellular domain, evading trastuzumab binding while constitutively activating downstream signaling. Splicing mutation (c.1899-1G>A): Leads to exon skipping, altering the HER2 protein structure	Reduced antigen expression, antigen masking, antigen truncation, target mutations, and antigen internalization. Markedly reduced drug-binding affinity. Sustained activation of downstream oncogenic signaling. Therapeutic escape facilitated by intratumoral heterogeneity	Switch to agents with distinct mechanisms (e.g., ADCs). Implement dual HER2 blockade (e.g., trastuzumab + pertuzumab). Employ NGS to guide therapy selection	Schiff et al[96]; Chen et al[97]; O'keefe et al[98]; Jebbink et al[99]; Jiao et al[100]; Marchiò et al[101]; Sperinde et al[102]; Goh et al[103]; Janiszewska et al[104]
Aberrant downstream pathway activation	PIK3CA H1047R mutation: Sustains PI3K/AKT/mTOR signaling despite HER2 blockade. PTEN loss: Leads to constitutive PI3K pathway activation. NF1 loss/KRAS mutation: Activates the RAS/MAPK pathway, driving resistance via the MEK-CDK2 axis	Bypasses upstream HER2 inhibition, maintaining survival and proliferation signals. Alters oncogenic dependency, driving cell cycle progression	Combine PI3K/mTOR inhibitors (e.g., alpelisib). Combine MEK inhibitors (e.g., trametinib). Combine CDK4/6 or explore CDK2 inhibitors	Schiff et al[96]; Janiszewska et al[104]; Smith and Chandarlapaty[105]; Yu et al[106]; Garay et al[107]; Garay et al[108]; Smith et al[109]
Cell survival related mechanisms	AKT-mediated phosphorylation: Inhibits pro-apoptotic proteins (e.g., BAD, caspase-9), blocking mitochondrial apoptosis (cytochrome c release). AKT/mTOR signaling: Promotes G1/S transition by regulating cyclin D1/CDKs and downregulating p27Kip1	Induces an “apoptosis-resistant” phenotype, elevating cell survival threshold. Disrupts cell cycle checkpoints, enabling continuous proliferation (reflected by elevated Ki-67)	Target persistent downstream survival signals (e.g., with AKT inhibitors). Exploit cell cycle vulnerabilities (e.g., with CDK inhibitors)	Smyth et al[3]; Bang et al[8]; Gravalos and Jimeno[9]; Friedlaender et al[22]; Sareyeldin et al[23]; Dumitru et al[24]; Jensen et al[25]; Wang et al[110]; Bassi et al[111]
Bypass signaling activation	MET amplification/overexpression: Provides potent alternative survival signaling. FGFR pathway activation: Suppresses apoptosis and induces angiogenesis and EMT. AXL upregulation: Induced by hypoxia, promotes EMT and immune resistance. ER-HER2 crosstalk: Mediates cross-resistance via the CDK4/6-Rb axis	Establishes independent signaling circuits for proliferation and survival. Fuels malignant progression and facilitates immune evasion	Co-administer MET, FGFR, or AXL inhibitors. For HR+ patients, combine CDK4/6 inhibitors with endocrine therapy. Modulate the TME (e.g., alleviate hypoxia)	Pernas and Tolaney[35]; Schiff et al[96]; Szymczyk et al[112]; Wang et al[113]; Recondo et al[114]; Mami-Chouaib et al[115]; Koirala et al[116]; Mahdi et al[117]; Shagisultanova et al[118]; Clark et al[119]
Tumor heterogeneity	Spatial heterogeneity: Non-uniform HER2 expression within a tumor, risking sampling error in biopsies. Temporal heterogeneity: Clonal evolution under therapeutic pressure selects for resistant subpopulations	Inherent treatment failure due to untargeted cell populations. Leads to acquired resistance and disease relapse	Perform multi-region biopsy for accurate assessment. Utilize liquid biopsy for dynamic monitoring. Initiate potent combination regimens (e.g., dual HER2 blockade)	Schiff et al[96]; Wang et al[113]; Suenaga et al[120]
Tumor microenvironment remodeling	Metabolic reprogramming: Enhanced glycine/serine metabolism supports one-carbon units and nucleotide synthesis. Immunosuppression: Dysfunctional TILs and upregulated immune checkpoints. ECM remodeling: Integrin-mediated pro-survival signaling	Provides biosynthetic precursors and energy for tumor growth. Creates a physical and immunosuppressive barrier against therapy	Target key metabolic enzymes. Combine immune checkpoint inhibitors. Develop novel strategies targeting the ECM	Schiff et al[96]; Abuelreich et al[121]

HER2: Human epidermal growth factor receptor 2; TKI: Tyrosine kinase inhibitor; PI3K: Phosphatidylinositol 3-kinase; AKT: Protein kinase B; mTOR: Mammalian target of rapamycin; MAPK: Mitogen-activated protein kinase; MEK: Mitogen-activated protein kinase kinase; CDK: Cyclin-dependent kinase; MET: Mesenchymal-epithelial transition factor; FGFR: Fibroblast growth factor receptor; EMT: Epithelial-mesenchymal transition; ER: Estrogen receptor; TIL: Tumor-infiltrating lymphocyte; ECM: Extracellular matrix; NGS: Next-generation sequencing; ADC: Antibody-drug conjugate; HR: Hormone receptor; TME: Tumor microenvironment.

Table 5 Resistance mechanisms to anti-human epidermal growth factor receptor 2 antibody-drug conjugates and emerging counterstrategies

Resistance mechanism	Key molecular/cellular processes	Consequences	Potential overcoming strategies	Ref.
Alterations in target antigen expression	HER2 protein expression levels. Spatial and temporal tumor heterogeneity	Subpopulations with low/no HER2 evade ADC binding, leading to therapeutic escape. Dynamic downregulation under therapeutic pressure drives acquired resistance	Implement dynamic HER2 status monitoring (e.g., via liquid biopsy). Develop ADCs effective against HER2-low tumors. Explore bispecific antibodies or therapies targeting alternative antigens	Ocaña et al[129]
Impaired drug transport	Receptor-mediated endocytosis. ADC intracellular trafficking. Drug efflux pumps (e.g., P-glycoprotein)	Impaired ADC internalization prevents payload delivery. Efflux pumps reduce intracellular payload concentration, diminishing cytotoxicity	Engineer ADCs with improved internalization efficiency. Develop payloads resistant to common efflux pumps. Investigate combination therapies with efflux pump inhibitors	Alrhmoun and Sennikov[32]; Mahalingaiah et al[130]; Chen et al[131]
Lysosomal dysfunction	Lysosomal protease activity. Intralysosomal pH. Lysosomal membrane permeability	Inefficient linker cleavage and payload release, even after successful internalization. Altered pH environment inactivates the payload	Design linkers optimized for specific lysosomal proteases. Utilize pH-sensitive linkers that release payload in early endosomes, bypassing lysosomal dependency	Chen et al[131]; Liu-Kreyche et al[132]
Payload-specific resistance	DDR pathways. Expression of the payload’s molecular target. Activity of drug-metabolizing enzymes	Enhanced DDR capacity repairs payload-induced DNA damage (e.g., from topoisomerase I inhibitors). Target mutation/downregulation reduces payload binding and efficacy. Enzymatic inactivation of the payload	Develop novel payloads with unique mechanisms of action to bypass pre-existing resistance. Combine ADCs with targeted agents (e.g., PARP inhibitors for DDR). Engineer ADCs with dual, synergistic payloads	Alrhmoun and Sennikov[32]; Chen et al[131]; Ceci et al[133]

HER2: Human epidermal growth factor receptor 2; ADC: Antibody-drug conjugate; DDR: DNA damage response; pH: Potential of hydrogen; PARP: Poly-adenosine diphosphate ribose polymerase.

Table 6 A comprehensive framework for biomarker-driven precision medicine in human epidermal growth factor receptor 2-positive gastric cancer

Core domain	Key technologies/strategies	Clinical application and value	Current limitations and challenges	Ref.
Standardized HER2 testing	IHC; FISH/CISH; NGS	IHC is the primary screening method. FISH/CISH confirm gene amplification. NGS provides a comprehensive genomic profile (e.g., HER2 amp, mutations, co-alterations like PIK3CA)	Subjectivity in IHC interpretation. Tumor heterogeneity leading to false-negatives. Chromosome 17 polysomy confounding FISH. NGS is not yet a routine primary test	Jebbink et al[99]; McLemore et al[134]; Taylor et al[135]; Klc et al[136]; Ciesielski et al[137]; Vermij et al[138]
Liquid biopsy	ctDNA; CTCs; exosomes	Enables dynamic monitoring of resistance and evolution. ctDNA tracks HER2 status and resistance mutations. CTC enumeration and phenotyping reflect tumor burden	Variable sensitivity in early-stage disease. Lack of standardization across platforms. Integration strategy with tissue biopsy is not yet defined	Ho et al[139]; Koessler et al[140]; Rossi and Ignatiadis[141]; Li et al[142]; Massihnia et al[143]
Integrated multi-omics analysis	Genomics; transcriptomics; proteomics	Provides a holistic view of tumor biology. Identifies molecular subtypes for targeted therapies (e.g., ADCs). Guides rational combination strategies	Requires bioinformatics expertise. High cost challenges routine use. Needs prospective validation for clinical utility	Yuan et al[144]; Pfeifer and Schimek[145]; Kerr and Yang[146]; Bueno et al[147]
Future directions	AI; biomarker-driven individualized framework	AI enhances IHC objectivity and integrates multi-omics for predictive modeling. Establishes refined molecular characterization to guide personalized therapy intensity	AI models require large-scale data for validation. Translating novel biomarkers requires interdisciplinary collaboration and workflow redesign	Jebbink et al[99]; Yuan et al[144]; Bueno et al[147]

HER2: Human epidermal growth factor receptor 2; IHC: Immunohistochemistry; FISH: Fluorescence in situ hybridization; CISH: Chromogenic in situ hybridization; NGS: Next-generation sequencing; ctDNA: Circulating tumor DNA; CTC: Circulating tumor cell; AI: Artificial intelligence; ADC: Antibody-drug conjugate.