Available evidence indicates that METTL3 is upregulated in EC tissues, with the clearest and most consistent data coming from ESCC (35-37). Both immunohistochemistry and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analyses demonstrate that METTL3 mRNA and protein levels are significantly elevated in ESCC tumors compared with matched adjacent non-tumorous mucosa (38-40). Moreover, elevated METTL3 expression is significantly associated with lymph node metastasis and more advanced tumor-node-metastasis (TNM) stage in patients with ESCC (41,42). Public database analyses further support this observation: Studies based on Gene Expression Omnibus (GEO; https://www.ncbi.nlm.nih.gov/geo/) microarray datasets and The Cancer Genome Atlas (TCGA; https://www.cancer.gov/ccg/research/genome-sequencing/tcga) transcriptomic data consistently demonstrate that METTL3 is broadly upregulated in ESCC and is closely associated with aggressive malignant phenotypes, including deeper invasion, metastasis and poor prognosis (38,42-44). By contrast, direct evidence regarding the expression profile of METTL3 in EAC remains far more limited. Current clues are derived mainly from mixed EC cohorts or stratified database analyses, which suggest that aberrant METTL3 expression may also be present in EAC (45). However, large-scale clinical tissue-based studies in EAC, particularly those providing systematic validation at the protein level, are still lacking. Therefore, the precise expression landscape of METTL3 in EAC, as a distinct histological subtype, remains to be further clarified.

Despite METTL3 is frequently upregulated in ESCC and is closely associated with adverse clinicopathological features, including lymph node metastasis, advanced TNM stage, and poor prognosis, its upstream regulatory mechanisms in EC remain insufficiently characterized (42,46). Current evidence suggests that the widespread epigenetic reprogramming observed in ESCC, together with m⁶A-dependent post-transcriptional regulation, may collectively contribute to the development of METTL3-associated aberrant phenotypes (47-49). Nevertheless, direct experimental evidence obtained in rigorously subtype-defined ESCC models remains insufficient to determine whether histone acetylation/deacetylation directly regulates METTL3 expression, or whether non-coding RNAs act as stable upstream regulators of METTL3 (50). Therefore, the upstream regulation of METTL3 should presently be regarded as an evolving frontier in EC research rather than a mechanistically fully resolved component of EC biology.

Current clinical and translational evidence consistently supports the pathological and clinical relevance of METTL3 in ESCC. Elevated METTL3 expression has been significantly associated with adverse clinicopathological features, including advanced TNM stage, lymph node metastasis, deeper invasion and unfavorable survival outcomes across multiple cohorts and public datasets (38,42-44). Several studies have further suggested that METTL3 may serve as an independent adverse prognostic factor in ESCC; however, this interpretation should be made with caution because of differences in cohort size, analytical methodology and multivariable adjustment strategies among available studies (40,51). Beyond its prognostic significance, emerging preclinical evidence indicates that METTL3 may also participate in the regulation of treatment response, particularly in the context of radiotherapy resistance, whereas its value as a clinically actionable predictive biomarker remains to be established (52-54). By contrast, the clinical significance of METTL3 in EAC remains insufficiently characterized. At present, the available evidence is inadequate to determine whether METTL3 has prognostic or predictive relevance comparable to that observed in ESCC, or whether its biological functions are largely histological subtype-dependent (55). Therefore, future studies using well-annotated EAC clinical specimens are required to define the clinical and biological significance of METTL3 in this distinct subtype.

To date, the most convincing mechanistic evidence in EC comes from ESCC models, predominantly highlighting the canonical m⁶A-dependent functions of METTL3 (56-58). Rather than operating through a singular universal downstream pathway, METTL3 drives malignant progression via transcript-specific modulation of RNA stability, splicing and translation (35). Several critical molecular axes have been unequivocally established. For instance, METTL3-mediated m⁶A deposition upregulates NOTCH1 expression, triggering Notch signaling to facilitate tumor proliferation and progression (38). In parallel, METTL3 stabilizes early growth response 1 (EGR1) transcripts in a YTH domain family protein (YTHDF) 3-dependent manner, activating the EGR1/Snail pathway to promote epithelial-mesenchymal transition (EMT) and metastatic dissemination (37,59). Regarding metabolic reprogramming, METTL3 induces the m⁶A-dependent, YTHDF2-mediated decay of adenomatous polyposis coli (APC) transcripts; this suppresses APC expression, prompting β-catenin accumulation and the subsequent hyperactivation of c-Myc- and pyruvate kinase M2 (PKM2)-driven glycolysis (48).

Recent ESCC-specific studies have further expanded this intricate mechanistic landscape (Fig. 2). Notable discoveries include the YTH domain-containing protein 1 (YTHDC1)-dependent regulation of adhesion molecule with Ig-like domain 2 (AMIGO2) pre-mRNA splicing, the direct transcriptional modulation of interferon-induced protein with tetratricopeptide repeats 2 (IFIT2), and the insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2)-mediated stabilization of interferon alpha-inducible protein 27 (IFI27) (46,60,61). Additional validated networks encompass family with sequence similarity 135 member B (FAM135B) -associated Wnt/β-catenin hyperactivation (62), double homeobox A pseudogene 8 (DUXAP8)-mediated phosphoinositide 3-kinase (PI3K)/Protein Kinase B (AKT) signaling (63) and mitogen-activated protein kinase (MAPK)-linked cascades involving collagen type XII alpha 1 chain (COL12A1) and WAS protein family member 3 (WASF3) (40). Collectively, these empirical findings substantiate a model wherein METTL3 orchestrates ESCC progression by integrating multiple, parallel RNA-centric regulatory networks that synergistically govern proliferation, invasion, metabolic adaptation and therapeutic response.

A subset of studies has delineated METTL3 regulatory mechanisms using generalized EC cohorts that lack explicit ESCC or EAC annotation. Prominent examples include the broad hyperactivation of AKT signaling, the YTHDF1-dependent translational enhancement of tubulointerstitial nephritis antigen-like 1 (TINAGL1), and the IGF2BP2-mediated stabilization of PIK3CA transcripts (64-66). While these molecular events may ultimately prove relevant to specific EC subtypes, the absence of stringent histological stratification fundamentally limits the validity of any subtype-specific inferences. Consequently, these pathways must be strictly classified as 'EC-associated' rather than 'ESCC-established'. This rigorous distinction is critical in a research landscape disproportionately skewed toward ESCC, where an unwarranted assumption of biological equivalence across fundamentally divergent subtypes could severely misguide future translational efforts (Fig. 2).

Conversely, numerous METTL3-associated mechanisms frequently cited in contemporary EC reviews rely heavily on evidence extrapolated from other malignancies and remain wholly unverified within the esophageal context (21,67,68). Prominent among these are the cytoplasmic, m⁶A-independent (or catalysis-independent) functions of METTL3, which reportedly enhance translation via direct physical interactions with ribosomes, eukaryotic translation initiation factor 3 (eIF3), or PABPC1 (69,70). Additional highly discussed but unvalidated paradigms in EC encompass specific long non-coding RNA (lncRNA) sponge networks, the direct transcriptional upregulation of programmed death-ligand 1 (PD-L1), the chemokine-driven recruitment of immunosuppressive macrophages, and the exosomal transfer of METTL3 derived from cancer-associated fibroblasts (71-74). Although the existence of analogous pathways in LC (75), GC (76), leukemia (77) and colorectal cancer (78) renders these mechanisms biologically plausible in EC, theoretical plausibility must not be conflated with empirical proof. Until definitive causality is established using authenticated, subtype-defined ESCC or EAC models, these molecular pathways must be rigorously framed as theoretical cross-cancer extrapolations rather than established drivers of esophageal carcinogenesis (Fig. 2).

Available evidence links METTL3 to metabolic adaptation in ESCC via at least two distinct mechanistic avenues. First, METTL3-mediated m⁶A deposition accelerates the decay of APC transcripts, consequently hyperactivating the β-catenin/c-Myc/PKM2 axis to drive glycolytic reprogramming (48). Second, METTL3 reportedly upregulates glutaminase 2 (GLS2) expression, further sustaining migratory and invasive phenotypes in ESCC cells (44). While these findings highlight METTL3's contribution to metabolic flexibility, several clinically relevant observations remain purely correlative. For instance, statistical associations between METTL3 expression and ¹⁸F-fluorodeoxyglucose uptake, glucose transporter 1 (GLUT1) expression, or hexokinase 2 (HK2) abundance are compelling (45). However, they do not inherently prove direct, transcript-level control of glucose or lactate metabolism. Therefore, while a role for METTL3 in ESCC metabolic reprogramming is strongly supported, the comprehensive network of its downstream effectors awaits definitive characterization.

Acquired chemoresistance remains a primary cause of treatment failure in ESCC (79,80). Within this context, METTL3 has emerged as a pivotal regulator of apoptosis and therapeutic response (81-83). Direct functional evidence demonstrates that METTL3 attenuates paclitaxel sensitivity by modulating the caspase 9 (CASP9) and baculoviral IAP repeat containing 3 (BIRC3) pathways, mechanistically linking m⁶A epitranscriptomic rewiring to the suppression of treatment-induced apoptosis (54). Consistently, the pharmacological inhibition of METTL3 profoundly sensitizes preclinical ESCC models to paclitaxel. These observations underscore that METTL3 functions not solely as a classical oncogenic driver, but actively dictates treatment tolerance (84). This paradigm shift is conceptually critical, situating METTL3 at the crucial nexus of oncogenic signaling and adaptive resistance, thereby providing a strong biological rationale for synergistic combination therapies.

Radiotherapy constitutes a cornerstone of ESCC management, and emerging data have begun to elucidate the critical role of METTL3 in governing radiosensitivity and DDR (85-88). Direct mechanistic evidence has shown that, in radioresistant ESCC models, METTL3-mediated m⁶A modification stabilizes the lncRNA activating regulator of DKK1 (LNCAROD) in a YTHDC1-dependent manner (89). Upregulated LNCAROD subsequently maintains poly(ADP-ribose) polymerase 1 (PARP1) protein stability by facilitating the PARP1-nucleophosmin 1 interaction, thereby enhancing homologous recombination repair and promoting radioresistance (89). In parallel, m⁶A-modified circular RNAs have also been implicated in the regulation of radiotherapeutic response in ESCC. For example, circular RNA derived from CREB binding lysine acetyltransferase (circCREBBP) enhances radiosensitivity by reducing MYC mRNA stability through an IGF2BP3-related mechanism (90). On the other hand, the METTL3 inhibitor STM2457 has been shown to activate ataxia-telangiectasia mutated (ATM)/checkpoint kinase 2 (Chk2)/phosphorylated histone H2AX (γ-H2AX)-associated DDR signaling and suppress tumor cell growth in ESCC cells, suggesting that METTL3 may participate in balancing DNA damage tolerance and treatment response (91). However, current evidence supporting the combination of METTL3 inhibitors with radiotherapy or DNA damage repair-targeted agents remains largely confined to preclinical inference, and further direct studies are required to validate this therapeutic strategy. Collectively, these findings establish METTL3 as a central arbiter balancing DNA damage tolerance with treatment-induced cytotoxicity, fortifying the translational rationale for integrating METTL3 inhibitors with radiotherapy or DNA damage repair-targeted agents (Fig. 2).

The involvement of METTL3 in EMT, invasion and stemness-associated traits in ESCC is most rigorously supported when contextualized within subtype-validated pathways (35). Specifically, METTL3 orchestrates metastatic dissemination via the EGR1/Snail axis, amplifies proliferative and migratory capacities through AMIGO2 regulation, and sustains sphere-forming potential by stabilizing IFI27 transcripts (59-61,92). Additionally, FAM135B-dependent Wnt/β-catenin hyperactivation further potentiates plasticity-related phenotypes in ESCC (62). At the same time, broader claims that METTL3 universally regulates EMT or cancer stemness through classical mediators such as transforming growth factor beta, zinc finger E-box binding homeobox 1, SRY-box transcription factor 2, octamer-binding transcription factor 4 and Nanog homeobox are derived mainly from other cancer types (93-95). While conceptually relevant, these canonical pathways currently lack rigorous validation in authenticated ESCC models. From a strictly evidence-based perspective, METTL3 is most accurately defined not as an indiscriminate driver of EMT, but as a context-dependent amplifier of phenotypic plasticity, uniquely poised to drive tumor adaptation under conditions of therapeutic stress.

Although the TIME plays a central role in immune evasion in ESCC, current evidence linking METTL3 to the ESCC TIME is still derived predominantly from TCGA/GEO-based bioinformatic analyses and correlative clinical observations (96-98). Available studies suggest that METTL3 expression, or m⁶A regulator-associated signatures, is statistically associated with immune cell infiltration, PD-L1-related phenotypic states, and immune scoring parameters, thereby indicating its potential value as an immune-associated biomarker (99,100). However, direct functional evidence in rigorously defined ESCC models remains limited and is still insufficient to establish METTL3 as a stable driver of immune escape, checkpoint regulation, M2 macrophage polarization, or fibroblast-dependent intercellular transfer in this subtype (101). Notably, recent studies at the level of EC have suggested that METTL3 may participate in M2 macrophage polarization and PD-L1-associated regulation, although whether these findings are directly applicable to strictly defined ESCC systems requires further validation. Therefore, at present, METTL3 is more appropriately regarded as a candidate immune-associated biomarker in ESCC rather than a mechanistically established immunoregulatory driver, and its immunological functions still require more systematic functional investigation.

At present, direct evidence supporting the therapeutic potential of METTL3 is derived predominantly from preclinical models of ESCC, whereas EAC-specific data remain markedly limited. Available studies have shown with reasonable consistency that genetic depletion or pharmacological inhibition of METTL3 significantly suppresses ESCC cell proliferation, migration, invasion and in vivo tumorigenicity. Mechanistically, the most solid evidence in ESCC supports the involvement of METTL3 in Notch pathway activation (38), APC/β-catenin-associated glycolytic reprogramming (48), and the regulation of downstream effectors such as IFIT2. In addition, the proposed involvement of EGR1/Snail (35), AMIGO2, IFI27, and several more recently described effector axes has further expanded the downstream network governed by METTL3 (44,46,63). Nevertheless, these findings should still be interpreted with appropriate caution from an evidence-based perspective (102). Several frequently cited mechanisms, including broad immune-checkpoint regulation or certain receptor tyrosine kinase/AKT-associated translational control pathways, are currently supported far more strongly in other cancer types than in ESCC, where an equally robust mechanistic framework has not yet been established (26,72). Therefore, although METTL3 represents a highly promising candidate therapeutic target in ESCC, its actionable dependency is likely to remain strongly context-dependent and pathway-specific (Table II).

Among the pharmacological studies reported to date, the catalytic METTL3 inhibitor STM2457 and the repurposed drug elvitegravir represent the most representative ESCC-specific pharmacological evidence currently available (59,91). Existing studies have shown that STM2457 significantly suppresses ESCC cell proliferation and migration, induces G0/G1 cell-cycle arrest and apoptosis, and activates the ATM-Chk2-associated DDR (91). Moreover, when combined with paclitaxel, STM2457 exhibits enhanced antitumor activity in both in vitro and in vivo models. By contrast, elvitegravir inhibits ESCC metastasis by promoting STUB1-dependent proteasomal degradation of METTL3. Taken together with recent mechanistic studies involving the CASP9/BIRC3, LNCAROD/PARP1 and circCREBBP/MYC regulatory axes, the available evidence suggests that METTL3-targeted therapy may be of particular value in paclitaxel-treated or radioresistant ESCC (54,89,90). Nevertheless, evidence supporting combination strategies integrating METTL3 inhibition with radiotherapy or DDR-targeted agents remains largely confined to the preclinical setting, and further direct studies are required to validate these therapeutic approaches. These critical observations support the development of combination strategies which strategically integrate METTL3 inhibition with taxanes, conventional radiotherapy, or DDR-directed pharmacological agents.