Gastric epithelial neoplasm of fundic-gland mucosa lineage: representative of the low atypia differentiated gastric tumor and Ki67 may help in their identification.

Background: Gastric epithelial neoplasm of the fundic-gland mucosa lineages (GEN-FGMLs) are rare forms of gastric tumors that encompass oxyntic gland adenoma (OGA), gastric adenocarcinoma of the fundic-gland type (GA-FG), and gastric adenocarcinoma of the fundic-gland mucosa type (GA-FGM). There is no consensus on the cause, classification, and clinicopathological features of GEN-FGMLs, and misdiagnosis is common because of similarities in symptoms. Methods: 37 cases diagnosed with GEN-FGMLs were included in this study. H&E-stained slides were reviewed and clinicopathological parameters were recorded. Immunohistochemical staining was conducted for MUC2, MUC5AC, MUC6, CD10, CD56, synaptophysin, chromograninA, p53, Ki67, pepsinogen-I, H+/K+-ATPase and Desmin. Results: The patients' ages ranged from 42 to 79 years, with a median age of 60. 17 were male and 20 were female. Morphologically, 19 OGAs, 16 GA-FGs, and two GA-FGMs were identified. Histopathological similarities exist between OGA, GA-FG, and GA-FGM. The tumors demonstrated well-formed glands, expanding with dense growth patterns comprising pale, blue-grey columnar cells with mild nuclear atypia. These cells resembled fundic gland cells. None of the OGA invaded the submucosal layer. The normal gastric pit epithelium covered the entire surface of the OGA and GA-FG, but the dysplasia pit epithelium covered the GA-FGM. Non-atrophic gastritis was observed in more than half of the background mucosa. All cases were diffusely positive for MUC6 and pepsinogen-I on immunohistochemistry. H+/K+-ATPase staining was negative or showed a scattered pattern in most cases. MUC5AC was expressed on the surface of GA-FGMs. p53 was focally expressed and the Ki67 index was low (1%-20%). Compared with OGA, GA-FG and GA-FGM were more prominent in the macroscopic view (p < 0.05) and had larger sizes (p < 0.0001). Additionally, GA-FG and GA-FGM exhibited higher Ki67 indices than OGA (p < 0.0001). Specimens with Ki-67 proliferation indices >2.5% and size >4.5 mm are more likely to be diagnosed with GA-FG and GA-FGM than OGA. Conclusion: GEN-FGMLs are group of well-differentiated gastric tumors with favourable biological behaviours, low cellular atypia, and low proliferation. Immunohistochemistry is critical for confirming diagnosis. Compared with OGA, GA-FG and GA-FGM have larger sizes and higher Ki67 proliferation indices, indicating that they play a critical role in the identification of GEN-FGML. Pathologists and endoscopists should be cautious to prevent misdiagnosis and overtreatment, especially in biopsy specimens.

Comparison of Prognosis and Metachronous Gastric Tumor Rates After Endoscopic Submucosal Dissection Between Gastric Neoplasm of Fundic Gland Type Neoplasms and Conventional Gastric Adenocarcinoma.

INTRODUCTION: Gastric neoplasm of the fundic gland type (GNFG) is a tumor with a good prognosis. However, since it has not been compared with conventional gastric adenocarcinoma (CGA), it is unknown whether it has a good prognosis or requires surveillance after treatment. The purpose of this study was to determine the prognosis and metachronous gastric tumor rates compared with those of CGA. METHODS: We conducted a single-center, retrospective, matched-cohort study using our database from January 2010 to December 2021. We extracted GNFG data from the endoscopic submucosal dissection (ESD) database and matched patients with conventional early gastric cancer as controls in a 1:4 ratio by age and sex. GNFG and CGA were compared for the overall survival (OS), disease-specific survival, progression-free survival, and metachronous gastric tumor rates. RESULTS: Overall, 43 lesions were GNFG and 164 CGAs were matched. There were three deaths in the GNFG group and 11 deaths in the CGA group. There was no significant difference in the OS between the two groups (P=0.81). The five-year OS rates for the GNFG and CGA groups were 90.9% and 92.9%, respectively. No disease-specific deaths or recurrences were observed in either group. There was no significant difference in the cumulative metachronous gastric tumor rate between the two groups (P=0.17). The cumulative five-year metachronous gastric tumor rates for the GNFG and CGA groups were 6.6% and 2.5%, respectively. CONCLUSIONS: The prognosis for GNFG is good, however, not better than that for CGA. The metachronous gastric tumor rate after ESD in GNFG was not lower than that in CGA. Therefore, after ESD, GNFG may need to be managed in the same way as CGA.

Prevalence, clinical characteristics and treatment outcomes of oxyntic gland neoplasm: a single-center retrospective study.

BACKGROUND: Oxyntic gland neoplasm (OGN) is a rare subtype of gastric cancer. The aim of this study is to evaluate the prevalence, clinicopathological features, effectiveness and safety of endoscopic treatment, as well as the prognosis of OGN. METHODS: We retrospectively analyzed the data of patients pathologically diagnosed with OGN at our hospital from November 1, 2019 to May 1, 2023. RESULTS: A total of 36 patients with 45 lesions were identified, resulting in a disease frequency of 0.047% (36/76,832). The mean age was 55.0 ± 7.5 years, with a male-to-female ratio of about 1:1.12. Most lesions were ≤10 mm in size (84.4%), located in the upper third of the stomach (73.3%), exhibited slight elevation (75.5%), appeared whitish (55%), had dilated blood vessels on the surface (75.5%). 16 and 21 lesions were treated by precutting endoscopic mucosal resection (EMR-P) and endoscopic submucosal dissection (ESD), respectively. No significant differences were found between EMR-P and ESD in terms of en bloc resection rate (100% vs 100%, p = 1.000), complete resection rate (100% vs 90.5%, p = 0.495), and curative resection rate (93.8% vs 90.5%, p = 1.000). No complications such as bleeding and perforation were observed. No recurrence or metastasis was observed during the follow-up period. CONCLUSIONS: OGN is a rare tumor with unique clinical, endoscopic, and pathological characteristics. EMR-P and ESD are deemed safe and effective for treating OGNs. The relatively faster and easier EMR-P seems at least non-inferior to ESD, especially for removal of smaller OGNs. The overall prognosis is favorable.

Pathology and Clinical Relevance of Gastric Epithelial Dysplasia.

Gastric dysplasia is defined as an unequivocally neoplastic epithelium. Dysplastic lesions are characterized by cellular atypia reflective of abnormal differentiation and disorganized glandular architecture. The last few years have been marked by a refinement of the prognosis and risk of progression of gastric dysplasia and the recognition of novel morphologic patterns of dysplasia. Determination of the correct diagnosis and grade of dysplasia are critical steps since it will be predicting the risk of malignant transformation and help tailor appropriate surveillance strategy. This review describes the morphologic characteristics of conventional dysplasia and nonconventional gastric dysplasia that have been more recently characterized.

Oxyntic Gland Adenoma in a Patient With Refractory Reflux.

A 58-year-old African American male was referred for endoscopic evaluation due to a persistent nine-year history of reflux. Previous endoscopy nine years ago revealed a small hiatal hernia and chronic gastritis caused by Helicobacter pylori (H. pylori), which was treated with triple therapy. During the current endoscopic evaluation, findings consistent with reflux esophagitis were identified, along with the discovery of an incidental 6 mm sessile polyp in the gastric fundus. Pathological examination revealed the presence of an oxyntic gland adenoma (OGA). Otherwise, the stomach was found to be unremarkable endoscopically and histologically. OGA is a rare gastric neoplasm that is primarily observed in Japan, with very few reported cases in North America. Studies have suggested a potential association with antacids, while the role of H. pylori in the development of OGA remains controversial. Our patient's OGA was completely resected during the endoscopy, with no recurrence noted on the three-month follow-up.

Lesion size, elevated morphology, and non or closed-type atrophy are predictive factors for gastric adenocarcinoma of the fundic gland type rather than oxyntic gland adenoma.

Background: An oxyntic gland neoplasm confined to the mucosal layer (T1a) is classified as an oxyntic gland adenoma, whereas that with submucosal invasion (T1b) is defined as gastric adenocarcinoma of the fundic gland type (GA-FG). Methods: To reveal the differences in clinical features between them, we retrospectively investigated 136 patients with 150 oxyntic gland adenoma and GA-FG lesions. Results: The univariate analysis revealed that the mean size (GA-FG vs. oxyntic gland adenoma, 7.7±5.4 vs. 5.5±3.1 mm), the prevalence of elevated morphology (79.1% vs. 51.8%), black pigmentation within the lesion (23.9% vs. 9.6%), and non or closed-type atrophy (81.2% vs. 65.1%) were different between the two groups. A multivariate logistic regression analysis revealed that ≥5 mm lesion size (odds ratio, 2.96; 95% confidence interval: 1.21-7.23), elevated morphology (odds ratio, 2.40; 95% confidence interval: 1.06-5.45), and no or closed-type atrophy (odds ratio, 2.49; 95% confidence interval: 1.07-5.80) were factors in distinguishing GA-FG from oxyntic gland adenoma. When oxyntic gland neoplasms with no or one feature were judged as oxyntic gland adenomas and those with two or three features were judged as GA-FG, the sensitivity and specificity were 85.1% and 43.4% for GA-FG, respectively. Conclusions: We identified three possible distinctive features of GA-FG compared to oxyntic gland adenoma: lesion size ≥5 mm, elevated morphology, and no or closed-type atrophy.

Clinicopathological Features and the Prevalence of Oxyntic Gland Neoplasm: A Single-center Retrospective Study.

Objective We explored the clinicopathological characteristics and disease frequency of oxyntic gland neoplasms (OGNs). Methods We retrospectively evaluated the data of patients pathologically diagnosed with OGN at an internal medicine clinic. Patients A total of 13,240 upper gastrointestinal endoscopies were performed on 7,488 patients between December 1, 2017, and March 31, 2021. Results We identified 27 patients with 30 histopathologically confirmed OGNs, yielding a disease frequency of 0.36% (27/7,488). Furthermore, multiple simultaneous lesions were found in 3 of 27 patients (11%). One (3.3%) of the 30 lesions was present in the antrum, whereas the remaining lesions occurred in the body of the stomach. Nine (33%) of the 27 patients had no history of Helicobacter pylori infection, whereas the remaining 18 (67%) were either currently or had been previously infected. Nevertheless, 27/30 lesions (90%) still occurred in non-atrophied regions. After endoscopic treatment, a histopathological examination of the resected specimens revealed submucosal infiltration in 8 (44%) of the 18 lesions; however, none of the lesions showed submucosal desmoplasia. For all patients with submucosal involvement, only observation was performed. There were no recurrent lesions found on follow-up. Conclusion The period prevalence of OGN was 0.36%, which is much higher than previously reported. The discovery of a small submucosal appearing lesion with a faded yellow or white color and dilated microvasculature, especially in a non-atrophic area of the stomach, should raise suspicion for an OGN, which can be endoscopically managed.

Clinical effects and pathological characteristics of gastric tumors of fundic gland type treated with endoscopic submucosal dissection / 中华消化内镜杂志

To evaluate the clinical effects and pathological characteristics of gastric tumors of fundic gland type treated with endoscopic submucosal dissection (ESD), data of 7 patients who treated by ESD and whose postoperative pathology indicated gastric adenocarcinoma of fundic gland type or gastric oxyntic gland adenoma in Endoscopic Center of Beijing Chao-Yang Hospital of Capital Medical University from August 2018 to June 2022 were collected. The clinical characteristics, surgical complications, preoperative and postoperative pathological data and follow-up data were evaluated. The lesions of the 7 patients were all located at gastric fundus, and were treated by ESD successfully. No bleeding, perforation or other complications occurred during and after the operation. Postoperative pathology showed that tumor cells originated from deep mucosa with an invasive growth pattern. Most of tumor surfaces were covered with normal concave epithelium. Tumors infiltrated into submucosa in 4 patients, and submucosa infiltration depth was more than 500 μm (550 μm) in 1 patient. Immunohistochemistry showed that MUC-6 was diffusely positive, indicating that the tumor originated from the main cell source. The expressions of MUC-2, MUC-5AC, CDX-2, CD10, and CgA were negative in all cases. With the mean follow-up time of 21 months, the ulcer healed well after the operation, with no recurrence. Gastric tumors of fundic gland type have relatively unique biological characteristics, and ESD is the preferred treatment. In addition, the histological characteristics can be used to differentiate from other gastric tumors by immunohistochemistry.

Endoscopic Features of Gastric Epithelial Neoplasm of Fundic Gland Mucosa Lineage.

The endoscopic features of gastric epithelial neoplasms of fundic gland mucosa lineage (GEN-FGML) have not been well investigated. We aimed to clarify the endoscopic features of GEN-FGML and differences between gastric adenocarcinoma of the fundic gland type (GA-FG) and fundic gland mucosa type (GA-FGM). A total of 62 GEN-FGML lesions, including 52 GA-FG and 10 GA-FGM, were retrospectively analyzed using endoscopic and clinicopathological findings to provide information of diagnostic value using white light imaging (WLI) and magnifying endoscopy with narrow-band imaging (M-NBI). GA-FG frequently presented with a whitish, submucosal tumor (SMT) shape with dilated vessels with branching architecture and background mucosa without atrophic change in WLI, an indistinct demarcation line (DL), dilatation of the crypt opening and intervening part (IP), and microvessels without distinct irregularity in M-NBI. GA-FGM frequently presented as a reddish, elevated lesion in WLI, with a distinct DL, dilatation of the IP, and an irregular microvascular pattern in M-NBI. As for an M-NBI diagnosis, five GA-FGM lesions met the diagnostic criteria for cancer, whereas none of the GA-FG lesions met the same criteria. We highlight the endoscopic features of GEN-FGML, and the differentiation between GA-FG and GA-FGM might be possible by combination of lesion color and morphology in WLI and M-NBI diagnoses.

Endoscopic features of oxyntic gland adenoma and gastric adenocarcinoma of the fundic gland type differ between patients with and without Helicobacter pylori infection: a retrospective observational study.

BACKGROUND: The endoscopic features of oxyntic gland adenoma and gastric adenocarcinoma of the fundic gland type have not been fully investigated in relation to Helicobacter pylori infection status. We compared the morphology, color, and location of these lesions between patients with and without H. pylori infection. METHODS: We retrospectively enrolled 165 patients (180 lesions) from 10 institutions. We divided the patients into the (i) Hp group (patients with current H. pylori infection [active gastritis, n = 13] and those with past infection [inactive gastritis, n = 76]) and (ii) uninfected group (H. pylori-uninfected patients, n = 52). We compared the clinical and endoscopic features of the two groups. We also performed an analysis between (i) lesions with atrophy of the surrounding gastric mucosa (atrophy group) and (ii) lesions without atrophy of the surrounding gastric mucosa (non-atrophy group). RESULTS: The average age was older in the Hp group than in the uninfected group (68.1 ± 8.1 vs. 63.4 ± 8.7 years, p < 0.01). Although the difference was not statistically significant (p = 0.09), multiple lesions were observed in 9 of 89 patients (10.1%) in the Hp group and in only 1 of 52 patients (1.9%) in the uninfected group. Meanwhile, significant differences were observed in the prevalence of lesions located in the gastric fornix or cardia (uninfected group: 67.3% vs. Hp group: 38.0%, p < 0.01), with an elevated morphology (80.0% vs. 56.0%, p < 0.01), with a subepithelial-like appearance (78.2% vs. 42.0%, p < 0.01), and with a color similar to that of the peripheral mucosa (43.6% vs. 25.0%, p = 0.02). The male-to-female ratio, lesion size, and presence or absence of vascular dilatation or black pigmentation on the surface were not different between the two groups. In the analysis comparing lesions with and without mucosal atrophy, the prevalence of multiple lesions was significantly higher (p = 0.02) in the atrophy group (5/25 patients, 20.0%) than in the non-atrophy group (7/141 patients, 5.0%). CONCLUSIONS: The endoscopic features of oxyntic gland adenoma and gastric adenocarcinoma of the fundic gland type differ between patients with and without H. pylori infection.

Gastric epithelial neoplasm of fundic-gland mucosa lineage: proposal for a new classification in association with gastric adenocarcinoma of fundic-gland type.

BACKGROUND: Gastric adenocarcinoma of fundic-gland type (GA-FG) is a rare variant of gastric neoplasia. However, the etiology, classification, and clinicopathological features of gastric epithelial neoplasm of fundic-gland mucosa lineage (GEN-FGML; generic term of GA-FG related neoplasm) are not fully elucidated. We performed a large, multicenter, retrospective study to establish a new classification and clarify the clinicopathological features of GEN-FGML. METHODS: One hundred GEN-FGML lesions in 94 patients were collected from 35 institutions between 2008 and 2019. We designed a new histopathological classification of GEN-FGML using immunohistochemical analysis and analyzed via clinicopathological, immunohistochemical, and genetic evaluation. RESULTS: GEN-FGML was classified into 3 major types; oxyntic gland adenoma (OGA), GA-FG, and gastric adenocarcinoma of fundic-gland mucosa type (GA-FGM). In addition, GA-FGM was classified into 3 subtypes; Type 1 (organized with exposure type), Type 2 (disorganized with exposure type), and Type 3 (disorganized with non-exposure type). OGA and GA-FG demonstrated low-grade epithelial neoplasm, and GA-FGM should be categorized as an aggressive variant of GEN-FGML that demonstrated high-grade epithelial neoplasm (Type 2 > 1, 3). The frequent presence of GNAS mutation was a characteristic genetic feature of GEN-FGML (7/34, 20.6%; OGA 1/3, 33.3%; GA-FG 3/24, 12.5%; GA-FGM 3/7, 42.9%) in mutation analysis using next-generation sequencing. CONCLUSIONS: We have established a new histopathological classification of GEN-FGML and propose a new lineage of gastric epithelial neoplasm that harbors recurrent GNAS mutation. This classification will be useful to estimate the malignant potential of GEN-FGML and establish an appropriate standard therapeutic approach.

[Clinical pathological characteristics of 4 cases of gastric gland-derived tumors].

Objective: To investigate the pathological features of gastric tumor originated from the fundic gland, including oxyntic gland adenoma (OGA) and gastric adenocarcinoma of the fundic gland (GA-FG). Methods: A retrospective analysis of 2 cases of OGA and 2 cases of GA-FG admitted to our hospital from February 2019 to September 2019 was performed. The histological features were analyzed by immunohistochemical staining combined with endoscopic observation. Results: The four cases arose from the deep layer of the lamina propria mucosae and well differentiated. Two cases of OGA confined to the mucosa, including 1 case of irregular tubules showing low-degree dysplasia and another case of irregular branching and anastomosing tubules showing high-degree dysplasia. Two cases of GA-FG combined with submucosal invasion, showed irregular branching and anastomosing tubules and formed a so-called "endless glands" pattern. Atypia, helicobacter pylori (HP) infection, chronic gastritis, intestinal metaplasia, or gastric atrophy were not observed in the superficial epithelium covering the tumor extent. Two cases of OGA and 2 cases of GA-FG showed the same result of immunohistochemical staining: pepsinogen-1 was diffusely positive in the tumor tissues and indicated chief cell differentiation, while positive ATPase and PDGFRA-α indicated parietal cells differentiation. The expression of Syn were positive in all cases, while CD10, MUC2 and CD-X2 were negative. The upregulation of p53 protein or nuclear positivity of ß-catenin was not observed. The Ki-67 labeling index in the hot area was approximately 1-5%. Conclusions: GA-FG is a well-differentiated, low-grade malignant novel subtype of gastric cancer. The immunohistochemical markers and narrowband imaging combined with magnifying endoscopy (NBI-ME) enhance the diagnostic sensitivity. Whether Syn positive expression can be one of the diagnostic item needs to be further investigate. The process of tumorigenesis of GA-FG might be the transition from low-grade dysplasia to high-grade dysplasia of OGA and further to submucosal infiltration. However, the mechanism of GAFG was still unclear. Disregulation of the Shh and Wnt/ß-catenin signaling pathway might be associated with tumorigenesis of GA-FG. Endoscopic submucosal dissection (ESD) is often the preferred and curative treatment.

Helicobacter Infection and Gastric Adenoma.

BACKGROUND: We aimed to provide insight into the actual frequencies of gastric adenoma types and their association with gastritis status and associated mucosal changes with a focus on Helicobacter infection and the operative link on gastritis assessment (OLGA)/operative link on gastric intestinal metaplasia assessment (OLGIM) staging. METHODS: From the archive of the Institute of Pathology in Bayreuth, we collected a consecutive series of 1058 gastric adenomas diagnosed between 1987 and 2017. Clinicopathological parameters retrieved from diagnostic reports included adenoma type and localization, associated mucosal changes in antrum and corpus (i.e., type of gastritis, the extent of intestinal metaplasia and atrophy), gender, date of birth, and date of diagnosis. RESULTS: Intestinal-type adenoma was the most frequent adenoma (89.1%), followed by foveolar-type adenoma (4.3%), pyloric gland adenoma (3.4%), adenomas associated with hereditary tumor syndromes (2.8%), and oxyntic gland adenoma (0.4%). Adenomas were found in the background of Helicobacter pylori (H. pylori) gastritis in 23.9%, Ex-H. pylori gastritis in 36.0%, autoimmune gastritis in 24.8%, chemical reactive gastritis in 7.4%, and others in 0.1%. More than 70% of patients with gastric adenomas had low-risk stages in OLGA and OLGIM. CONCLUSIONS: We found a higher frequency of foveolar-type adenoma than anticipated from the literature. It needs to be questioned whether OLGA/OLGIM staging can be applied to all patients.

Morphology and genetics of pyloric gland adenomas in familial adenomatous polyposis.

AIMS: Gastric pyloric gland adenomas (PGAs) are rare epithelial polyps that are found more commonly in autoimmune atrophic gastritis and familial adenomatous polyposis (FAP). Little is known about the morphology and genetics of PGAs in FAP. PGAs in FAP are studied morphologically and genetically. Findings in FAP-associated PGAs are compared to sporadic PGAs and related lesions such as oxyntic gland adenoma (OGA) to increase our understanding of these rare polyps. METHODS AND RESULTS: Seven PGAs and 18 fundic gland polyps (FGPs) from FAP patients were collected. KRAS and GNAS mutations were determined in six PGAs and 18 FGPs. Immunohistochemistry was applied on five PGAs to provide further confirmation of the histological subtypes and genetic alterations. Morphology of all PGAs was studied and compared to literature on sporadic PGAs and related lesions. All successfully sequenced PGAs (six of six) carried GNAS mutations and half of the successfully sequenced PGAs carried a KRAS mutation (three of six). Nuclear ß-catenin was seen only in one PGA with focal high-grade dysplasia. Morphologically, PGAs in FAP showed overlapping features with OGA. CONCLUSION: Familial adenomatous polyposis-associated PGAs have a similar genetic background as sporadic PGAs, i.e. KRAS and GNAS mutation. Based on morphological findings in FAP associated PGAs, it is hypothesized that PGAs and OGAs are closely related lesions.

Oxyntic Gland Adenoma Treated by Endoscopic Mucosal Resection

Oxyntic gland polyp/adenoma is a recently reported rare neoplasm previously called gastric adenocarcinoma of fundic gland type (chief cell predominant type). We report a case of oxyntic gland adenoma curatively treated with endoscopic mucosal resection. On endoscopy, a small, round polypoid lesion was observed in the fundus of the stomach of a 33-year-old man. He underwent endoscopic mucosal resection with a cap for diagnostic and therapeutic purposes, and was diagnosed as having oxyntic gland adenoma with high-grade dysplasia. On immunohistochemical analysis, the tumor was positive for MUC6 and negative for MUC5AC and MUC2. Our case suggests that endoscopic mucosal resection with immunohistochemical analysis might be useful for correctly diagnosing an uncertain lesion suspected as an oxyntic gland adenoma.

Oxyntic gland adenoma endoscopically mimicking a gastric neuroendocrine tumor: A case report.

Gastric adenocarcinoma is one of the most common malignancies worldwide. Histochemical and immunohistologic analyses classify the phenotypes of gastric adenocarcinoma into several groups based on the variable clinical and pathologic features. A new and rare variant of gastric adenocarcinoma with chief cell differentiation (GA-CCD) has recently been recognized. Studies reporting the distinct clinicopathologic characteristics proposed the term oxyntic gland polyp/adenoma because of the benign nature of the GA-CCD. Typically, GA-CCD is a solitary mucosal lesion that develops either in the gastric cardia or fundus. Histologically, this lesion is characterized by tightly clustered glands and anastomosing cords of chief cells. Immunohistochemically, GA-CCD is diffusely positive for mucin (MUC) 6 and negative for MUC2 and MUC5AC. However, other gastric tumors such as a gastric neuroendocrine tumor or fundic gland polyp have been difficult to exclude. Because GA-CCD tends to be endoscopically misdiagnosed as a neuroendocrine tumor or fundic gland polyp, comprehensive assessment and observation by an endoscopist are strongly recommended. Herein, we report a rare case of oxyntic gland adenoma endoscopically mimicking a gastric neuroendocrine tumor that was successfully removed by endoscopic mucosal resection.