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Review Undifferentiated-type early gastric cancer: from margin demarcation to complete resection
Satoru Mizutaniorcid, Seiichiro Abeorcid, Yutaka Saitoorcid

DOI: https://doi.org/10.5946/ce.2026.062
Published online: August 10, 2026

Department of Endoscopy, National Cancer Center Hospital, Tokyo, Japan

Correspondence: Seiichiro Abe Department of Endoscopy, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan E-mail: seabe@ncc.go.jp
• Received: February 17, 2026   • Revised: April 23, 2026   • Accepted: May 8, 2026

© 2026 Korean Society of Gastrointestinal Endoscopy

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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  • Gastric cancer remains a major global health burden, particularly in Asia, where widespread implementation of endoscopic screening has increased the detection of early gastric cancer (EGC). With advances in endoscopic techniques, endoscopic resection (ER), especially endoscopic submucosal dissection, has become the standard treatment for EGC with a negligible risk of lymph node metastasis (LNM). Undifferentiated-type EGC (UD-EGC) is associated with a higher risk of LNM than differentiated-type EGC. However, favorable long-term outcomes can be achieved with curative resection. Despite this, accurate endoscopic detection, characterization, and delineation of UD-EGC remain a challenge because of their subtle morphology and unique growth pattern. Image-enhanced endoscopy, particularly magnifying endoscopy with narrow-band imaging, plays an important role in diagnosis and assessment of the lateral extent of the lesion. In Japan, accumulating evidence, including prospective multicenter trials, has led to the classification of intramucosal UD-EGC ≤2 cm without ulceration, as an absolute indication for ER in the latest clinical guidelines. Short and long-term outcomes after curative ER for UD-EGC are comparable to those after surgical resection. This review summarizes the current literature on the diagnosis and endoscopic management of UD-EGC, providing a comparative overview of differences in endoscopic treatment recommendations among international guidelines.
  • Keywords: Endoscopic mucosal resection; Endoscopy; Stomach; Stomach neoplasms
Gastric cancer (GC) ranks fifth in incidence and mortality worldwide, with 968,000 new cases and 659,000 deaths reported globally in 2022, the highest rates of which are observed in Asia.1
In Japan, population-based screening programs have been actively implemented, and endoscopic screening has become prevalent.2 As a result, the detection rate of early gastric cancer (EGC) has increased. With improvements in the detection of EGC, endoscopic resection (ER), especially endoscopic submucosal dissection (ESD), is currently widely performed in EGC patients with a negligible risk of lymph node metastasis (LNM).3
The prevalence of Helicobacter pylori (H. pylori) infection has been declining in Japan, and accordingly, the relative proportion of H. pylori-uninfected GC has been increasing.4 As a result of this epidemiological shift, the proportion of H. pylori–uninfected undifferentiated EGC (UD-EGC) may increase in the future, making accurate diagnosis and optimal treatment of UD-EGC more important.
Currently, ER is indicated for clinically diagnosed intramucosal (cT1a) UD-EGC ≤20 mm in size without ulceration (UL0).5,6 UD-EGC has been reported to have a higher risk of LNM compared to differentiated EGC (D-EGC).7 However, favorable long-term outcomes can still be obtained after curative resection.8-10 Therefore, early and precise endoscopic diagnosis, and appropriate therapeutic management of UD-EGC are crucial for achieving optimal clinical outcomes.
This review focuses on the current literature and future perspectives regarding the diagnosis and treatment of UD-EGC.
According to the World Health Organization classification, common histological types of gastric epithelial tumors are papillary adenocarcinoma, tubular adenocarcinoma, poorly differentiated adenocarcinoma, signet-ring cell carcinoma and mucinous adenocarcinoma.11 The Japanese Gastric Cancer Association (JGCA) categorizes gastric adenocarcinomas into two groups: differentiated and undifferentiated. The differentiated group consists of tubular and papillary adenocarcinoma. The undifferentiated group consists of poorly differentiated, signet-ring cell and mucinous adenocarcinoma. Some GCs exhibit a complex admixture of differentiated and undifferentiated components, and such cancers should be classified according to the predominant histologic type.12 EGC with mixed-type histology has been reported to be associated with an increased risk of LNM.13,14 In 847 intramucosal EGCs, LNM was significantly higher in mixed-type than in pure differentiated-type tumors (5.1% vs. 0.5%, p<0.001). Among submucosal cancers, LNM rates were 13%, 21%, and 33% in pure differentiated-type, pure undifferentiated-type, and mixed-type EGC, respectively (p<0.05).7,15
According to the JGCA guidelines, the criteria for endoscopic treatment differ for D-EGC and UD-EGC due to their different risks of LNM.6 Therefore, diagnosing whether the cancer is differentiated or undifferentiated is essential for determining the treatment strategy for EGC. As a general principle, a definitive diagnosis of cancer and determination of its histological type should be made by histopathological examination of a biopsy specimen and the tissue obtained after ER.16 Additionally, it should be noted that when histological typing is based on biopsy, a discrepancy rate of 1.5%–8.0% is found compared to the final diagnosis.17-19
Although early detection of UD-EGC remains challenging, it is essential for achieving curative ER. UD-EGCs are predominantly located in the middle to lower thirds of the stomach. On white-light imaging (WLI), UD-EGC lesions often present as subtle superficial lesions that can mimic gastritis, making them difficult to detect.20 Compared to D-EGC, UD-EGC exhibits a discolored appearance and a flat or depressed morphology more frequently (Fig. 1).21
The utility of image-enhanced endoscopy (IEE) as a detection tool for EGC is still under investigation in large-scale studies.
The role of IEE in the characterization of suspicious lesions, particularly when combined with magnification, has been well established. Among these techniques, magnifying endoscopy with narrow-band imaging (ME-NBI) is valuable for the detailed assessment of suspicious lesions.22,23
The magnifying endoscopy simple diagnostic algorithm for gastric cancer (MESDA-G) is a well-established diagnostic method for distinguishing cancerous lesions from non-cancerous ones using ME-NBI. According to this algorithm, the presence of a well-demarcated margin, an irregular microsurface, and/or microvascular pattern under ME-NBI is highly suggestive of EGC.24-26
Most D-EGCs exhibit either full-thickness or superficial replacement growth, with neoplastic glands often reaching and exposing the mucosal surface, and these structural changes are directly reflected in the endoscopic microvascular patterns.27 Consistent with these histopathological characteristics, typical ME-NBI findings of D-EGCs exhibit a fine, regular microvascular network.28
Signet-ring cell carcinomas arise from the glandular neck region and extend laterally within the middle mucosal layer, often covered by non-neoplastic epithelium. Therefore, small lesions may show no apparent changes on the mucosal surface.29,30 As the tumor extends along the middle mucosal layer, portions of the surface foveolar epithelium become eroded and the intervening stroma expands, resulting in dilated foveolar structures. When the tumor infiltrates through the full thickness of the mucosa, it appears as a characteristic corkscrew pattern on ME-NBI (Fig. 2).28,31 Poorly differentiated adenocarcinomas include a solid type, which arises through de-differentiation from tubular or papillary adenocarcinoma; and a non-solid type, which is often derived from signet-ring cell carcinoma and other histologic types. Compared with signet-ring cell carcinoma, the lateral resection margin of poorly differentiated adenocarcinomas is generally easier to assess endoscopically.
In UD-EGCs, particularly signet-ring cell carcinomas, minimal tumor spread within the proliferative zone may not affect the superficial foveolar epithelium, resulting in an absence of detectable findings on ME-NBI. As a result, accurate delineation of the extent of the lesion can be difficult in certain cases.32-34 In such cases, practical approaches in clinical practice include obtaining four-point negative biopsies from the surrounding mucosa and performing wider-than-usual marking during ER.
Conventional endoscopic predictors of deeper invasion
Endoscopic findings suggestive of submucosal invasion in EGC are typically identified using conventional WLI, and their characteristics vary according to the macroscopic type.
In protruded-type (0–I) lesions, submucosal invasion is suggested by a lesion larger than 20 mm with a broad base, a nodular or irregular surface, deep depression, submucosal tumor-like elevation, and convergence or retraction of the surrounding folds.
Similarly, in superficial elevated-type (0–IIa) lesions, marked surface irregularities—such as prominent erosion, deep depression, thick whitish exudate, or nodular protrusions—are suggestive of submucosal invasion.
Superficial flat-type (0–IIb) lesions are mostly confined to the mucosa.
In depressed-type (0–IIc and 0–III) lesions, submucosal invasion is suggested by marked surface irregularities, including uneven nodules of varying size and prominent elevations within the depressed area. Moreover, a structureless surface is indicative of deep submucosal invasion. In addition, submucosal tumor-like elevation at the margins or in the surrounding area, forming a ridge-like appearance, may indicate submucosal invasion.
The limitations of endoscopic assessment in UD-EGC
UD-EGC may invade the submucosa without apparent surface changes, leading to underestimation, whereby submucosal cancers are misdiagnosed as intramucosal cancers.35,36
The potential role and limitations of endoscopic ultrasonography
The diagnostic accuracy of endoscopic ultrasonography (EUS) for assessing the depth of invasion in EGC, including UD-EGC, ranges from 66.4% to 78.0% across studies.37-39 In particular, EUS tends to overestimate the depth of invasion in lesions with ulceration or submucosal fibrosis.40 Therefore, it is not considered indispensable for preoperative depth assessment prior to ER.
The potential role and limitations of IEE
Submucosal invasion has been reported to be associated with findings on ME-NBI, including a blurry mucosal pattern, an irregular mesh pattern, and dilated vessels.41,42
However, as ME-NBI mainly evaluates surface mucosal structures, its diagnostic performance remains limited and has not been established for early submucosal invasion without surface changes or for UD-EGCs, which tend to lack apparent surface alterations.
Chromoendoscopy using indigo carmine enhances the contrast between cancerous and normal mucosa, thereby improving the visualization of subtle morphological features of gastric lesions, and allowing clear identification of the demarcation line.43 However, it has been reported that even with chromoendoscopy, approximately 20% of EGC lesions exhibit indistinct tumor margins.44 Although ME-NBI has been reported to enable complete circumferential delineation in 72.6% of lesions with indistinct margins on chromoendoscopy, a multicenter randomized trial including both ESD and surgical resection cases did not demonstrate the superiority of ME-NBI over chromoendoscopy (88.0% vs. 85.7%, p=0.63). Therefore, both indigo carmine chromoendoscopy and ME-NBI are considered comparably effective for assessing the lateral extent of EGC.45,46
For UD-EGCs, adding ME-NBI improved the ability to identify the demarcation line compared with WLI alone, in ESD and surgically resected cases (ESD: WLI 53.9%, ME-NBI+WLI 81.5%; surgery: WLI 47.3%, ME-NBI+WLI 83.8%), demonstrating that ME-NBI is more effective than conventional WLI for delineating lesion boundaries.34,47 In contrast, chromoendoscopy did not perform better than WLI for identifying the demarcation line in UD-EGCs.34,47,48 In UD-EGCs, the addition of ME-NBI to conventional WLI is expected to improve the accuracy of demarcation diagnosis. However, in atrophic mucosa, the assessment may remain difficult even with ME-NBI, as the degree of inflammation and atrophy can produce highly variable microvascular patterns. In such cases, the lateral extent should be assessed by complementing ME-NBI with WLI findings—such as slight discoloration, mild redness, or loss of visible vessels—and by confirming negative results on peripheral biopsies.
The 5-year disease-specific survival rates for patients who underwent gastrectomy with lymph node dissection were 99.3% for mucosal cancers, and 96.7% for submucosal invasive cancers.49 Considering the rate of surgery-related mortality and the 5-year disease-specific survival rate (99.3%), it was assumed that endoscopic treatments for mucosal cancers with an upper 95% confidence limit for LNM below 1%, could achieve survival outcomes comparable to those of surgical resection. Accordingly, these lesions are classified as absolute indications for ER in Japanese guidelines.50
Previously, only clinically diagnosed D-EGC (cT1a) ≤2 cm, UL0 was strongly recommended as an absolute indication for ER in the guidelines.
In a retrospective study of 3,843 patients with solitary UD-EGC who underwent gastrectomy with lymph node dissection, none of the 310 intramucosal lesions ≤2 cm without lymphovascular invasion or ulceration, were associated with LNM (95% confidence interval [CI], 0%–0.96%).51 Following this study, the JGCA guidelines (3rd edition, 2010) classified clinically diagnosed UD-EGC (cT1a) ≤2 cm, UL0 as an expanded indication for ESD.52
Multicenter prospective studies by the Japan Clinical Oncology Group (JCOG) 1009/1010 (a single-arm confirmatory trial of an expanded indication for ESD for UD-EGC) demonstrated that the 5-year overall survival (OS) after ESD was extremely favorable, suggesting outcomes comparable to those of surgical gastrectomy.53
Based on these findings, the JGCA guidelines (6th edition, 2021) reclassified UD-EGC (cT1a) ≤20 mm, UL0 as an absolute indication for ER.50
Several studies have reported that ER for UD-EGC achieved a high en bloc resection rate (91.4%–99.0%) with acceptable rates of adverse events, including delayed bleeding (3.3%–10.9%) and perforation (0.4%–4.1%). In contrast, the rate of curative resection has been reported to range from 55% to 82.5%, showing considerable variation among studies.53-58 However, most of these reports were based on retrospective analysis. A multicenter, prospective, confirmatory clinical trial (JCOG 1009/1010) evaluated the safety and efficacy of ESD for UD-EGC confined to the mucosa (cT1a) and measuring ≤2 cm in size.53 In this study, the en bloc resection rate achieved by ESD was 99%, the curative resection rate was 71%, and the rates of perforation and delayed bleeding were 5.7% and 6.8%, respectively. The difficulty in accurately diagnosing the lateral extent was considered one of the major challenges in performing ESD for UD-EGC. However, in the JCOG 1009/1010 study, both the en bloc and curative resection rates were high, and as a result of mandatory biopsies from outside the lesion before ESD, the proportion of horizontal margin positivity was only 3%.
The curability of ER is determined by two factors: the completeness of local resection and the possibility of LNM. In the latest JGCA guidelines (7th edition, 2025), endoscopic curability was classified into ‘eCuraA, B, C1, and C2,’ as shown in Figure 3. ‘eCuraA’ is a condition that can be considered as curative resection with equal or superior long-term outcomes compared to additional surgical resection, for which sufficient evidence is available.59,60 ‘eCuraB’ is a condition in which curability can be expected, although sufficient long-term outcomes have not been obtained. ‘eCuraC’ was originally known as non-curative resection, which may require additional treatment. ‘eCuraC’ is subdivided into ‘eCuraC-1’ and ‘eCuraC-2’: ‘eCuraC-1’ is a condition for D-EGC with merely positive lateral margin or piecemeal resection and a negligible risk of LNM. ‘eCuraC-2’ refers to cases that do not meet the criteria for endoscopic curability A, B, or C-1 and are considered to have a potential risk of LNM.
Lesions with undifferentiated-type predominant carcinoma measuring ≤2 cm, confined to the mucosa (pT1a), UL0, with negative horizontal and vertical margins (HM0 and VM0), and without lymphatic or vascular invasion (Ly0 and V0) were classified as eCuraB under the previous JGCA guidelines (5th edition, 2018). However, based on the results of JCOG 1009/1010, the JGCA guidelines (6th edition, 2021) reclassified UD-EGC fulfilling these pathological criteria as eCuraA.50,52
In cases of predominantly differentiated-type adenocarcinoma with pT1a, HM0, VM0, Ly0, and V0, lesions in which the undifferentiated component exceeds 2 cm in maximum diameter are classified as eCuraC-2.
Similarly, in predominantly differentiated-type adenocarcinoma ≤3 cm with pT1b (SM1; <500 μm from the muscularis mucosae), and with HM0, VM0, Ly0, and V0, the presence of an undifferentiated component within the submucosal invasive area is classified as eCuraC-2.
As a post-treatment management strategy following ER for UD-EGCs, patients with eCuraA undergo endoscopic surveillance once or twice a year. In cases of eCuraC (C-2), additional surgery is generally considered the standard treatment. If additional surgery is not selected due to age, comorbidities, or other factors, the risk of LNM is assessed.50
A simple risk scoring system, known as the eCura system, has been proposed, in which tumor size >30 mm, positive vertical margin (VM1), venous invasion (V1), and submucosal invasion ≥500 µm are each allocated 1 point, while lymphatic invasion (Ly1) is allocated 3 points. Based on the total score, LNM was observed in 2.5% of patients in the low-risk group (0–1 points), 6.7% in the intermediate-risk group (2–4 points), and 22.7% in the high-risk group (5–7 points) (Table 1).61 Based on this risk and the patient’s overall condition, the patient, the surgeon, and the gastroenterologist discuss and determine whether additional surgery should be performed.
In the validation set of the original eCura system study, 16% of patients had UD-EGC, with the majority being D-EGC. In a study reporting on patients with non-curative ER of UD-EGCs, LNM was observed in 2.6% of patients in the low-risk group (1–3 points), 10.9% in the intermediate-risk group (2–4 points), and 14.8% in the high-risk group (5–7 points), showing a significant trend across risk categories.62 These findings indicate that the eCura system can be appropriately applied to UD-EGC for stratifying LNM risk after non-curative ER.
The long-term outcomes after curative ER for UD-EGC are favorable, with 5-year OS rates of 93.0%–99.3% after curative ER and 82.5%–96.3% after non-curative ER. The local recurrence rate after curative ER for UD-EGC has been reported to be 0.4%–1.4%, and the rate of LNM to be 0%–0.6%. 53,54,56-58,63,64 For cT1a UD-EGC ≤2 cm, ER has been considered to achieve therapeutic outcomes comparable to surgery. In the prospective confirmatory JCOG 1009/1010 study, the 5-year OS rate of 275 patients with UD-EGC was 99.3% (95% CI, 97.1%–99.8%), and the 5-year relapse-free survival among eligible patients with UD-EGC was 98.9% (95% CI, 96.5%–99.6%). The 5-year OS in patients with UD-EGC was favorable, and no recurrence was observed among the 195 patients who underwent curative ESD. In a large multicenter prospective cohort study conducted in Japan (J-WEB/EGC), which prospectively followed 9,054 patients with 10,021 lesions who underwent ER through a web-based registration system, the 5-year OS rate for all patients who underwent ER was 89.0% (95% CI, 88.3%–89.6%). Among 226 patients with UD-EGC ≤2 cm, it was 94.2% (95% CI, 90.2%–96.6%), with a local recurrence rate of 0.4%, no metastatic recurrences, and no GC–related deaths.63
Although ER for UD-EGC has demonstrated therapeutic outcomes comparable to those of surgical resection, its stomach-preserving nature may predispose the remaining stomach to metachronous recurrence following curative resection. UD-EGC has been reported to be associated with a lower risk of metachronous recurrence compared with D-EGC. The 5-year cumulative incidence of metachronous gastric cancer (MGC) after curative ER for UD-EGC has been reported to range from 1.0% to 3.7%, whereas that for D-EGC is higher, ranging from 9.5% to 20%.64-68 This difference is considered to be attributable to variations in the degree of gastric atrophy and subsequent intestinal metaplasia.
Although Japanese, Korean, and European guidelines all recognize ER as the preferred treatment for EGC with negligible LNM risk, they differ in how strongly they endorse ER for UD-EGC (Table 2). These differences may reflect variations in the availability of prospective studies and differences in the threshold of acceptable risk of LNM for ER. In Japan, lesions with a risk of LNM of less than 1% are classified as absolute indications for ER. Based on the results of the JCOG1009/1010, a proactive approach has been adopted toward ER for UD-EGC (cT1a), ≤2 cm, UL0. In Europe, South Korea, and China, retrospective studies have indicated that UD-EGCs (cT1a, UL0, ≤20 mm) carry a low—but non-negligible—risk of LNM.64,69 Moreover, given that most evidence regarding the outcomes of ER for UD-EGCs originates from Japan, a cautious approach has been adopted when applying these findings to clinical practice. In Europe, UD-EGCs (cT1a, UL0, ≤20 mm) are regarded as expanded indications for ER. In contrast, in China and South Korea, ER is considered acceptable only after thorough discussion with the patient.
In North America, surgical resection is generally recommended, based on evidence indicating that the risk of LNM is higher than that in Asian populations.
Japan (JGCA guidelines)
According to the latest 7th edition of the JGCA guidelines, UD-EGC (cT1a), ≤2 cm, UL0 is classified as an absolute indication for ESD. Furthermore, when the pathological criteria of UD-EGC ≤2 cm, pT1a, UL0, HM0, VM0, Ly0, and V0 are all fulfilled, the risk of LNM is considered extremely low, and the resection is regarded as curative. After curative ER, endoscopic follow-up every six to 12 months is recommended, primarily for the detection of MGC. Based on this guideline, in Japan, ESD for UD-EGC meeting the absolute indication criteria has been established as the first-line treatment.52
Korea (Korean practice guidelines)
ER is recommended for D-EGC ≤2 cm, UL0. For D-EGC ≥2 cm, UL0, or those ≤3 cm with ulceration (UL1), either ESD or gastrectomy with lymph node dissection is indicated as the standard treatment. For UD-EGC ≤2 cm, ER should be considered with caution, and surgery is recommended as the standard treatment. To date, no prospective randomized controlled trials (RCTs) have compared long-term OS between gastrectomy with lymph node dissection and ER for UD-EGC ≤2 cm, cT1a. Retrospective studies have demonstrated that OS does not significantly differ between the two treatment modalities; however, the incidence of local recurrence is higher in the ER group.70-72 Accordingly, the Korean practice guidelines recommended gastrectomy with lymph node dissection as the standard treatment for UD-EGC.73 It further states that the evidence supporting ER for UD-EGC (cT1a, ≤2 cm) is limited, and prospective data remain insufficient. In Korea, a multicenter RCT comparing ER and surgical gastrectomy for UD-EGC (the ERASE-GC trial, NCT04890171) is currently underway, and its results are eagerly awaited.74
China (Chinese national clinical practice guidelines)
ER is generally recommended for EGC with an extremely low risk of LNM when en bloc resection is feasible. For UD-EGC, especially early gastric signet ring cell carcinoma, ESD is conditionally suggested because of the higher risks of incomplete resection and local recurrence.75
EU (European Society of Gastrointestinal Endoscopy guidelines)
According to the European Society of Gastrointestinal Endoscopy (ESGE) guidelines, ER is recommended as the first-line treatment for superficial gastric lesions in which the risk of LNM is considered to be zero or extremely low. ESD may be considered as a treatment option for UD-EGC that is cT1a, ≤2 cm, UL0. However, the ESGE guidelines state that the decision should be individualized, taking into account surgical risks and patient preferences. The guidelines further state that an en bloc R0 resection of ≤2 cm UD-EGC (pT1a, UL0, HM0, VM0, Ly0, V0) may be regarded as curative/low risk, with a LNM risk of <3%. In such cases, no additional treatment is generally required. However, because a small but real risk of LNM remains, complete staging is recommended. The guidelines emphasize that the decision for further therapy, including surgery, should be individualized and made within a multidisciplinary discussion, balancing the potential risk of LNM against the morbidity associated with additional treatment.5
United States (National Comprehensive Cancer Network guidelines/American Society for Gastrointestinal Endoscopy guidelines)
For D-EGC (cT1a) ≤2 cm, with histology showing well to moderately-differentiated adenocarcinoma, ER is recommended. Conversely, for UD-EGC, surgical resection is recommended regardless of tumor size or depth of invasion.76,77
While ESD is well established in Asia and Europe, there is relatively little high-quality ESD data from North America, and the risk of LNM in EGC patients in Western populations is considered higher than in Asia.78,79 Therefore, the indications for ER are determined with caution in North America.
In Japan, ER for UD-EGC is considered to provide therapeutic outcomes equivalent to surgery. However, recommendations regarding ER for UD-EGC vary among international guidelines, and further accumulation of clinical cases as well as the results of RCT studies are eagerly awaited.
Early detection and accurate assessment of invasion depth are crucial for the successful endoscopic management of UD-EGC, yet both remain difficult due to its subtle endoscopic appearance and growth pattern. Recently, artificial intelligence (AI) technologies, including deep learning and machine learning algorithms, have shown promising performance in the detection of GC, differentiation from gastritis, estimation of invasion depth and prediction of LNM risk.80-86 At present, there are few prospective RCTs evaluating AI for the diagnosis and management of UD-EGCs, and its routine use in clinical practice remains far from being established. However, the integration of AI into clinical practice is expected to further improve the diagnostic accuracy and management of UD-EGC in the near future.
IEE, including ME-NBI, is useful for diagnostic assessment of UD-EGCs; however, its limitations in lesion detection and delineation should be recognized. ER provides favorable therapeutic outcomes for UD-EGC (cT1a), ≤2 cm, UL0. In Japanese guidelines, ESD is recommended as a standard treatment for such lesions. However, recommendations for ER vary among regions other than Japan, and the results of ongoing RCTs are awaited to further establish its role.
Fig. 1.
Representative endoscopic images of undifferentiated-type early gastric cancer. (A) White-light imaging shows two closely adjacent, depressed, reddish lesions with indistinct margins. (B) Narrow-band imaging depicts the lesions as brownish areas. (C) After indigo carmine chromoendoscopy, the contrast between the lesions and the surrounding mucosa become clear. The yellow arrows indicate the margins of the two undifferentiated-type gastric cancers.
ce-2026-062f1.jpg
Fig. 2.
Magnifying narrow-band imaging of undifferentiated-type early gastric cancer. A corkscrew-like irregular microvascular pattern is observed.
ce-2026-062f2.jpg
Fig. 3.
Flowchart for evaluation of curability and therapeutic approach after ER of EGC according to the guidelines by JGCA (7th edition) and JGES (2nd edition). ER, endoscopic resection; EGC, early gastric cancer; JGCA, Japanese Gastric Cancer Association; JGES, Japanese Gastroenterological Endoscopy Society; M, cancer confined to mucosa; SM1, cancer with submucosal invasion depth <500 μm; UL0, without ulceration; UL1, ulceration; HM0, negative horizontal margin; HM1, positive horizontal margin; HMX, unevaluable horizontal margin; VM0, negative vertical margin; Ly0, no lymphatic invasion; V0, no vascular invasion; eCura, endoscopic curability; ESD, endoscopic submucosal dissection.
ce-2026-062f3.jpg
Table 1.
Classification by the eCura system and associated risk of LNM
Risk score Risk stratification
Total LNM rate (%) Category LNM rate (%) 5-year DSS rate (%)
0 1.6 Low 2.5 99.6
1 2.6
2 4.9 Middle 6.7 96.0
3 7.4
4 8.3
5 19.9 High 22.7 90.1
6 27.3
7 26.7

LNM, lymph node metastasis; DSS, disease-specific survival.

Table 2.
Comparison of international guidelines for undifferentiated-type early gastric cancer
Japan Korea China EU US
≤20 mm cT1a UL0 Absolute indication for ER Surgery preferred over ER Conditional indication for ER ER may be considered Surgery
Lesions not meeting the criteria Surgery Surgery Surgery Surgery Surgery

EU, European Union; US, United States; UL0, without ulceration; ER, endoscopic resection; cT1a, clinical tumor confined to the mucosa.

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        Undifferentiated-type early gastric cancer: from margin demarcation to complete resection
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      Undifferentiated-type early gastric cancer: from margin demarcation to complete resection
      Image Image Image
      Fig. 1. Representative endoscopic images of undifferentiated-type early gastric cancer. (A) White-light imaging shows two closely adjacent, depressed, reddish lesions with indistinct margins. (B) Narrow-band imaging depicts the lesions as brownish areas. (C) After indigo carmine chromoendoscopy, the contrast between the lesions and the surrounding mucosa become clear. The yellow arrows indicate the margins of the two undifferentiated-type gastric cancers.
      Fig. 2. Magnifying narrow-band imaging of undifferentiated-type early gastric cancer. A corkscrew-like irregular microvascular pattern is observed.
      Fig. 3. Flowchart for evaluation of curability and therapeutic approach after ER of EGC according to the guidelines by JGCA (7th edition) and JGES (2nd edition). ER, endoscopic resection; EGC, early gastric cancer; JGCA, Japanese Gastric Cancer Association; JGES, Japanese Gastroenterological Endoscopy Society; M, cancer confined to mucosa; SM1, cancer with submucosal invasion depth <500 μm; UL0, without ulceration; UL1, ulceration; HM0, negative horizontal margin; HM1, positive horizontal margin; HMX, unevaluable horizontal margin; VM0, negative vertical margin; Ly0, no lymphatic invasion; V0, no vascular invasion; eCura, endoscopic curability; ESD, endoscopic submucosal dissection.

      Fig. 1.

      Fig. 2.

      Fig. 3.

      Undifferentiated-type early gastric cancer: from margin demarcation to complete resection
      Risk score Risk stratification
      Total LNM rate (%) Category LNM rate (%) 5-year DSS rate (%)
      0 1.6 Low 2.5 99.6
      1 2.6
      2 4.9 Middle 6.7 96.0
      3 7.4
      4 8.3
      5 19.9 High 22.7 90.1
      6 27.3
      7 26.7
      Japan Korea China EU US
      ≤20 mm cT1a UL0 Absolute indication for ER Surgery preferred over ER Conditional indication for ER ER may be considered Surgery
      Lesions not meeting the criteria Surgery Surgery Surgery Surgery Surgery
      Table 1. Classification by the eCura system and associated risk of LNM

      LNM, lymph node metastasis; DSS, disease-specific survival.

      Table 2. Comparison of international guidelines for undifferentiated-type early gastric cancer

      EU, European Union; US, United States; UL0, without ulceration; ER, endoscopic resection; cT1a, clinical tumor confined to the mucosa.

      Table 1.

      Table 2.

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