An Immunohistochemical Analysis of Osteopontin and S100 Calcium-binding Protein P is Useful for Subclassifying Large- and Small-duct Type Intrahepatic Cholangiocarcinomas.

Intrahepatic cholangiocarcinoma (iCCA) has been newly subclassified into two different subtypes: large-duct (LD) type and small-duct (SD) type. However, many cases are difficult to subclassify, and there is no consensus regarding subclassification criteria. LD type expresses the highly sensitive diagnostic marker S100 calcium-binding protein P (S100P), while SD type lacks sensitive markers. We identified osteopontin (OPN) as a highly sensitive marker for SD type. This study aimed to develop new subclassification criteria for LD-type and SD-type iCCA. We retrospectively investigated 74 patients with iCCA and subclassified them based on whole-section immunostaining of S100P and OPN. Of the 74 cases, 41 were subclassified as LD type, 32 as SD type, and one was indeterminate. Notably, all S100P-negative cases had OPN positivity. Seventy-three of the 74 cases (98.6%) were clearly and easily subclassified as LD or SD type using only these 2 markers. We also determined the value of immunohistochemistry in cases that were difficult to diagnose based on hematoxylin-eosin and Alcian blue-periodic acid-Schiff staining. Furthermore, we analyzed the clinicopathological characteristics and prognoses of these 2 subtypes. LD type was a poor prognostic factor on univariate analysis; it had significantly worse overall survival (P= 0.007) and recurrence-free survival (P < 0.001) than the SD type. In conclusion, we propose new subclassification criteria for iCCA based on immunostaining of S100P and OPN. These criteria may help pathologists to diagnose subtypes of iCCA, supporting future clinical trials and the development of medications for these 2 subtypes as distinct cancers.

Diagnosis by combination of endoscopic findings helps differentiate non-Helicobacter pylori Helicobacter-infected gastritis from Helicobacter pylori-infected gastritis.

BACKGROUND: The characteristic endoscopic findings of non-Helicobacter pylori Helicobacter (NHPH) gastritis, including white marbled appearance and crack-like mucosa, have been reported. However, these findings can also manifest in H. pylori (HP)-infected gastritis. This study compared NHPH gastritis and mild atrophic HP gastritis to identify features that may enhance NHPH diagnosis. MATERIALS AND METHODS: A total of 2087 patients underwent upper gastrointestinal endoscopy and were histologically evaluated by multiple gastric mucosal biopsies according to the updated Sydney System (USS) at Shinshu University Hospital between 2005 and 2023. Among them, nine patients were classified into the NHPH group and 134 patients with HP infection and mild atrophy were classified into the HP group for retrospective comparisons of endoscopic findings and clinicopathological characteristics. RESULTS: All nine patients in the NHPH group (eight males [89%], median ± standard deviation [SD] age: 49 ± 13.0 years) were infected with H. suis. The 134 patients in the HP group contained 70 men (52%) and had a median ± SD age of 35 ± 19.9 years. Endoscopic findings were statistically comparable for white marbled appearance (three patients [33%] in the NHPH group and 37 patients [31%] in the HP group) and crack-like mucosa (three patients [33%] and 27 patients [20%], respectively). Diffuse redness was significantly less frequent in the NHPH group (one patient [14%] vs. 97 patients [72%], p < 0.001). White marbled appearance or crack-like mucosa without diffuse redness was significantly more common in the NHPH group (56% vs. 13%, p = 0.004), with a sensitivity and specificity of 56% and 87%, respectively. Mean USS neutrophil infiltration and Helicobacter density scores were significantly higher in the HP group (both p < 0.01), which might have influenced the endoscopic findings of diffuse redness. CONCLUSIONS: When endoscopic findings of white marbled appearance or cracked-like mucosa are present, evaluation for diffuse redness may contribute to a more accurate diagnosis of NHPH gastritis.

Mucosal damage in pancreaticobiliary maljunction is stronger in the gallbladder than in the bile duct.

BACKGROUND: The frequency of gallbladder carcinoma is high in pancreaticobiliary maljunction (PBM), and the mechanism of carcinogenesis is not well understood. METHODS: The expression of γH2AX, the most sensitive marker for detecting DNA damage, was analyzed using immunohistochemistry in patients with PBM, in which the gallbladder and bile duct were simultaneously resected. Gallbladder and bile ducts were evaluated in non-neoplastic regions in 13 cases of PBM without cancer in the gallbladder and bile ducts. RESULTS: The median frequencies of γH2AX expression in the bile duct and gallbladder within the same case were 5.9% (range 1.7-12.05%) and 9.9% (range 2.8-25%), respectively, and were significantly higher in the gallbladder mucosa (P < 0.0004). γH2AX expression strongly correlated in the bile duct and gallbladder (r = 0.9436, P < 0.0001). PBM caused marked mucosal damage to the gallbladder. CONCLUSIONS: Mucosal damage may be involved in carcinogenesis, which may be useful for predicting malignant transformation.

Artificial intelligence for evaluating the risk of gastric cancer: reliable detection and scoring of intestinal metaplasia with deep learning algorithms.

BACKGROUND AND AIMS: Gastric cancer (GC) is associated with chronic gastritis. To evaluate the risk, the Operative Link on Gastric Intestinal Metaplasia Assessment (OLGIM) system was constructed and showed a higher GC risk in stage III or IV patients, determined by the degree of intestinal metaplasia (IM). Although the OLGIM system is useful, evaluating the degree of IM requires substantial experience to produce precise scoring. Whole-slide imaging is becoming routine, but most artificial intelligence (AI) systems in pathology are focused on neoplastic lesions. METHODS: Hematoxylin and eosin-stained slides were scanned. Images were divided into each gastric biopsy tissue sample and labeled with an IM score. IM was scored as follows: 0 (no IM), 1 (mild IM), 2 (moderate IM), and 3 (severe IM). Overall, 5753 images were prepared. A deep convolutional neural network (DCNN) model, ResNet50, was used for classification. RESULTS: ResNet50 classified images with and without IM with a sensitivity of 97.7% and specificity of 94.6%. IM scores 2 and 3, involved as criteria of stage III or IV in the OLGIM system, were classified by ResNet50 in 18%. The respective sensitivity and specificity values of classifying IM between scores 0 and 1 and 2 and 3 were 98.5% and 94.9%, respectively. The IM scores classified by pathologists and the AI system were different in only 438 images (7.6%), and we found that ResNet50 tended to miss small foci of IM but successfully identified minimal IM areas that pathologists missed during the review. CONCLUSIONS: Our findings suggested that this AI system would contribute to evaluating the risk of GC accuracy, reliability, and repeatability with worldwide standardization.

Rising Trends of Endoscopic Barrett's Esophagus and Gastric Fundic Gland Polyps in Young Japanese Adults.

BACKGROUND/AIMS: This study examined changes in the esophageal-gastric junction and gastric mucosa in young Japanese adults undergoing endoscopy in the last 15 years. MATERIALS AND METHODS: This was a retrospective study of young Japanese adults (aged 19-30 years) who underwent esophagogastrod uodenoscopy between 2006 and 2020. The indications were upper gastrointestinal symptoms and anemia. Changes in the appearance of the esophago-gastric junction (i.e., the Z line and distal esophagitis) and gastric mucosa were examined. Endoscopic Barrett's esophagus was defined using the Japanese criteria. RESULTS: One thousand eight hundred forty-five patients were examined: 848 from 2006 to 2012 [400 males, mean age 26.5 years (range 19-30)] and 997 from 2013 to 2020 [433 males, mean age 26.2 years (range 19-30)]. The proportion showing endoscopic Barrett's esophagus and gastric fundic gland polyps increased significantly between the 2 periods (12.5% vs. 22.4%, P < .001; 3.4% vs. 7.2%, P < .001) with a significant correlation between the prevalence trends for endoscopic Barrett's esophagus and gastric fundic gland polyps (r = 0.789, P = .0008). Pathological examination showed that the prevalence of traditional fundic gland polyps unrelated to the use of proton pump inhibitors significantly increased from 40% (4/10) to 81% (25/31) between the 2 periods (P = .04). CONCLUSION: The prevalence of both endoscopic Barrett's esophagus and gastric fundic gland polyps among young Japanese adults significantly increased in the last 15 years. The trend in endoscopic Barrett's esophagus was significantly correlated with that of nonproton pump inhibitor-related gastric fundic gland polyps.

Interleukin-6 Stromal Expression is Correlated with Epithelial-Mesenchymal Transition at Tumor Budding in Colorectal Cancer.

Background. Tumor budding is a poor prognostic factor in colorectal adenocarcinoma, but the underlying mechanism remains unclear. Interleukin-6 (IL6) is one of the main cytokines produced by cancer-associated fibroblasts. IL6 is linked with cancer progression and poor prognosis by activating cancer cells and modifying the cancer microenvironment. However, little is known about the expression of IL6 in tumor budding and its association with tumor budding in colorectal adenocarcinoma. Methods. The clinicopathological and prognostic significance of IL6 in tumor budding was examined using a tissue microarray consisting of 36 patient samples of tumor budding in colorectal adenocarcinoma. IL6 mRNA was detected by RNAscope. Patients were stratified into negative and positive IL6 expression groups. Results. IL6 expression was overwhelmingly observed in cancer stroma but was negligible in cancer cells. Tumor budding grade was higher in the IL6-positive group in cancer stroma than in the IL6-negative group (P = .0161), while the IL6-positive group significantly exhibited the epithelial-mesenchymal transition phenotype compared with the IL6-negative group in cancer stroma (P = .0301). There was no significant difference in overall survival between colorectal adenocarcinoma patients in the IL6-positive and -negative groups in cancer stroma. Conclusion. Tumor budding may be affected by IL6 expression, and IL6 expression in cancer stroma at tumor budding may be an important prognostic marker.

Development of serological assays to identify Helicobacter suis and H. pylori infections.

Helicobacter suis, hosted by hogs, is the most prevalent gastric non-Helicobacter pylori Helicobacter species found in humans. Recent studies have suggested that H. suis infection has caused many cases of gastric disease, but the transmission route from hogs remains unclear. Diagnostic methods based on H. suis urease activity often yield negative results, and there is no reliable method for diagnosing H. suis infection in clinical practice without gastric biopsy specimens. This study presents the world's first use of whole-bacterial cell ELISA to simultaneously assess H. suis and H. pylori infections. The ELISAs showed high accuracy, with an area under the ROC curve of 0.96, 100% sensitivity, 92.6% specificity, 76.9% positive predictive value, and 100% negative predictive value for the H. suis test, and an area under the ROC curve of 0.92, 88.2% sensitivity, 87.5% specificity, 65.2% positive predictive value, and 96.6% negative predictive value for the H. pylori test.

ARL4C is associated with epithelial-to-mesenchymal transition in colorectal cancer.

BACKGROUND: ADP-ribosylation factor-like protein 4 C (ARL4C) is a member of the ARF small GTP-binding protein subfamily. The ARL4C gene is highly expressed in colorectal cancer (CRC). ARL4C protein promotes cell motility, invasion, and proliferation. METHODS: We investigated the characteristics of ARL4C by comparing its expression at the invasion front and relationships with clinicopathological data using RNAscope, a highly sensitive RNA in situ method. RESULTS: In all cases, ARL4C expression was observed in cancer stromal cells and cancer cells. ARL4C expression in cancer cells was localized at the invasion front. In cancer stromal cells, ARL4C expression was significantly stronger in cases with high-grade tumor budding than in cases with low-grade tumor budding (P = 0.0002). Additionally, ARL4C expression was significantly increased in patients with high histological grade compared with those with low histological grade (P = 0.0227). Furthermore, ARL4C expression was significantly stronger in lesions with the epithelial-to-mesenchymal transition (EMT) phenotype compared with the non-EMT phenotype (P = 0.0289). In CRC cells, ARL4C expression was significantly stronger in cells that had the EMT phenotype compared with those with a non-EMT phenotype (P = 0.0366). ARL4C expression was significantly higher in cancer stromal cells than in CRC cells (P < 0.0001). CONCLUSION: Our analysis reinforces the possibility that ARL4C expression worsens the prognosis of patients with CRC. Further elucidation of the function of ARL4C is desired.

IgG4 expression and IgG4/IgG ratio in the tumour invasion front predict long-term outcomes for patients with intrahepatic cholangiocarcinoma.

IgG4-positive plasma cells are reportedly increased in the tumour microenvironment, and a high number of these cells in tumours is a poor prognostic factor in several cancers. However, there are no reported analyses of IgG4 expression in intrahepatic cholangiocarcinoma (ICC). This study aimed to analyse the correlations between prognosis-related clinicopathological features of patients with ICC and IgG4 expression. We identified 37 ICC patients who underwent surgical resection between January 2010 and December 2020. The number of IgG-positive and IgG4-positive plasma cells in the tumour, invasion front, and stroma near the tumour was analysed by immunostaining. Furthermore, we examined the association of prognosis-related clinicopathological data with the number of IgG4-positive plasma cells and IgG4/IgG ratio in ICC patients. The IgG4-positive plasma cell percentages for the intra-tumour area, invasion front, and non-cancerous area (NCA) near the tumour were 91.9%, 56.8%, and 81.1%, respectively. IgG-positive plasma cells were observed in each region for all cases, except for NCA tissue in one case. A high IgG4 expression level and IgG4/IgG ratio in the invasion front were significantly associated with poor overall survival (OS) (log-rank test p=0.0438 and p=0.0338, respectively). Multivariate analysis for OS revealed that high IgG4 expression (p=0.0140), lymph node metastasis (p=0.0205), and positive surgical margin (p=0.0009) or a high IgG4/IgG ratio (p=0.0051), lymph node metastasis (p=0.0280), and positive surgical margin (p=0.0009) were independent poor prognostic factors. In conclusion, a high IgG4 expression level and IgG4/IgG ratio in the invasion front are independent poor prognostic factors for ICC. Targeted therapy for IgG4 may improve the prognosis for patients with ICC.

High expression of LGR6 is a poor prognostic factor in esophageal carcinoma.

BACKGROUND: Leucine-rich repeat-containing G-protein-coupled receptor 6 (LGR6) promotes carcinogenesis and progression in some cancer types. However, there are few reports of LGR6 expression in esophageal squamous cell carcinoma (ESCC). LGR6 expression and clinicopathological features in ESCC were investigated by RNAscope, a highly sensitive RNA in situ hybridization method. METHODS: Appropriate tumors were selected from 41 cases of ESCC from which tissue microarrays were generated, and LGR6 expression was identified by RNAscope. RESULTS: Thirty-seven patients had LGR6 expression. High LGR6 expression was observed in 17 cases and low LGR6 expression in 24 cases. LGR6 expression was significantly higher in high histological grade ESCC than in low histological grade ESCC (P = 0.0023). ESCC patients who received neoadjuvant chemotherapy had significantly higher LGR6 expression than those without neoadjuvant chemotherapy (P = 0.0109). Furthermore, high LGR6 expression showed a poorer prognosis than low LGR6 expression (log-rank test, P = 0.0365). CONCLUSIONS: LGR6 may be a prognostic factor and a potential new therapeutic target in ESCC.

Number and distribution of eosinophils and lymphocytes in the Japanese pediatric gastrointestinal tract: in search of a definition for "abnormally increased eosinophils".

BACKGROUND: Primary eosinophilic gastrointestinal disorders (EGIDs) constitute chronic allergic inflammation. The number of eosinophils is one of the diagnostic criteria; more than 20 eosinophils per high-power field (HPF) in the gastrointestinal (GI) tract are considered abnormal in Japan. However, the quantity of eosinophils considered normal varies according to anatomical location and geographical region; such values have not been reported in Japanese pediatric patients, nor have the numbers of lymphocytes in the normal pediatric stomach. To establish a reference for defining diagnostic criteria for EGIDs, we evaluated the number of eosinophils in the normal Japanese pediatric GI tract. METHODS: We examined 131 biopsy cases without significant clinical history, endoscopic abnormality, or histological abnormality. Immunohistochemical analysis of CD3 and CD20 was performed. RESULTS: The mean eosinophil density was highest in the cecum (49.5 ± 22.4 per HPF). Counts of more than 20 eosinophils per HPF were observed in the duodenum [bulb (20.0 ± 9.6) and second portion (30.0 ± 15.8)], terminal ileum (38.3 ± 22.7), cecum (49.5 ± 22.4), ascending colon (42.3 ± 25.3), transverse colon (29.4 ± 17.0), and descending colon (32.2 ± 17.9). Counts of fewer than 10 eosinophils per HPF were observed in the stomach and rectum; a count of fewer than one eosinophil per HPF was observed in the esophagus. More than 100 CD3-positive T cells per HPF were observed in the stomach. CONCLUSIONS: The mean numbers of eosinophils in the bowel were greater than 20 per HPF. For Japanese pediatrics, the current threshold eosinophil count should be revised.

Osteopontin expression in the invasive front stroma of colorectal adenocarcinoma is associated with tumor budding and prognosis.

BACKGROUND: Tumor budding (TB) is an important prognostic factor in colorectal carcinoma (CRC). Osteopontin (OPN) functions in various processes such as immune response, migration and invasion, angiogenesis, epithelial-mesenchymal transition (EMT) and metastasis. However, the involvement of OPN and CD44v6, which is a receptor for OPN, in TB has not been clarified. Therefore, we examined the relationship of OPN with TB in CRC and compared the clinicopathological features. METHODS: We investigated the expression of OPN and CD44v6 in 83 cases of CRC by immunostaining and analyzed the clinicopathological features. RESULTS: OPN expression was observed mostly in the cytoplasm of stromal cells such as macrophages and fibroblasts, and rarely in cancer cells. There was a significant correlation between OPN positivity and the degree of differentiation at the invasive front and TB grade. CD44v6 was positive in cancer cells in 72 cases (86.7 %) and negative in 11 cases (13.3 %). A statistically significant effect on overall survival (OS) was identified between the OPN-positive group [median OS: 1586 (range, 30-2749) days] and the OPN-negative group [median OS: 1901 (range, 8-2665) days] (log-rank test, p = 0.011). CONCLUSIONS: OPN analysis in CRC stromal cells may have prognostic implications.

Histopathologically defined intestinal metaplasia in lesser curvature of corpus prior to Helicobacter pylori eradication is a risk factor for gastric cancer development.

BACKGROUND AND AIM: Helicobacter pylori eradication has been shown to reduce the risk of gastric cancer (GC), with the number of eradication therapy cases on the rise. However, GC can still occur after successful treatment, and the histological differences prior to eradication in patients with and without GC are unclear. This study investigated the pre-treatment histological risk factors for GC development following eradication therapy. METHODS: We retrospectively enrolled consecutive adult patients diagnosed as having H. pylori infection between April 2004 and December 2018. Atrophy and intestinal metaplasia (IM) were histologically assessed according to the updated Sydney System. The operative link on gastritis assessment and the operative link on gastric intestinal metaplasia (OLGIM) were evaluated as well. RESULTS: Of the 247 patients analyzed in this study, 11 (4.5%) experienced GC after eradication therapy. Histological IM scores in the GC group were significantly higher at all gastric biopsy sites (p < .05), and the proportion of OLGIM III/IV stage was significantly greater in GC patients (81.8% vs. 31.8%, p < .01). For GC prediction, the area under the receiver operating characteristic curve for IM score at the lesser curvature of the corpus was the highest among all biopsy sites and not inferior to OLGIM results. CONCLUSIONS: Patients with histological IM prior to H. pylori eradication, especially at the lesser curvature of the corpus, may be at elevated risk for GC development after eradication therapy and require close surveillance.

A rare case of an enterochromaffin-like neuroendocrine tumor associated with parietal cell dysfunction treated using endoscopic submucosal dissection.

Most gastric neuroendocrine tumors (NETs) develop from enterochromaffin-like (ECL) cells. ECL-cell NETs are classically categorized into three types according to their etiology. A 50-year-old woman presented with submucosal tumor-like lesions in the stomach, which were identified via esophagogastroduodenoscopy. Although esophagogastroduodenoscopy and pathological findings of biopsy specimens showed an absence of mucosal atrophy in the body of the stomach, sticky, adherent, dense mucus was observed. All lesions were diagnosed as ECL-cell NETs based on histological examination findings; however, ECL-cell NETs did not apply to any of the classic types I-III categorization based on laboratory, computed tomography, and 24-h intragastric pH monitoring test findings. Endoscopic submucosal dissection of the tumor was performed. Pathological findings of the excised specimen indicated that parietal cell hyperplasia with a protrusion, dilated fundic glands, and endocrine cell hyperplasia in the background mucosa, and parietal cells were not immunostained for the α-subunits of H+/K+-ATPase. Genetic analysis identified mutation in the ATP4A gene. The patient opted for additional gastric resection due to the risk of lymph node metastasis with deeper submucosal invasion and vascular infiltration. This report describes the first case of ECL-cell NETs caused by parietal cell dysfunction, which was treated via endoscopic submucosal dissection.

Correlation of LGR5 expression and clinicopathological features in intrahepatic cholangiocarcinoma.

Leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5) is a known cancer stem cell marker. However, there are no reported analyses of LGR5 mRNA expression in normal liver and liver cancer tissues. Here, we evaluated LGR5 expression by RNAscope, a newly developed RNA in situ hybridization technique, using a tissue microarray consisting of 25 samples of intrahepatic cholangiocarcinoma (ICC) selected from the medical archives at our hospital. LGR5 expression levels were divided into high and low expression groups by the five-grade scoring system, and clinicopathological features were analyzed. Low LGR5 expression was identified in some normal hepatocytes and bile duct cells. In addition, LGR5 expression was identified in all bile duct cancer samples except one case. Well-differentiated to moderately-differentiated adenocarcinoma tended to show higher LGR5 expression than poorly-differentiated adenocarcinoma (P = 0.0561), and the large duct type showed significantly higher LGR5 expression levels than the small duct type (P = 0.0225). Patients in the high LGR5 expression group tended to have good overall survival (OS) (P = 0.0623). The Cox proportional hazard regression model revealed that the high LGR5 expression group showed independently better OS for ICC (P = 0.0285). High LGR5 expression is possibly a good prognosis factor in ICC. However, the detailed mechanism of LGR5 in this disease remains unclear, and further analysis is warranted.

Gastric adenocarcinoma arising from hamartomatous inverted polyp during 8-year follow-up.

Gastric hamartomatous inverted polyp (GHIP) is rare, with few reports of carcinogenesis from GHIP during long-term follow-up. A 51-year-old woman was diagnosed as having a submucosal tumor (SMT) during esophagogastroduodenoscopy (EGD) in 2008. In 2016, although the size and height of the lesion had not changed, she was referred to our hospital for further investigation of the lesion. EGD depicted a gastric SMT of 20 mm in diameter in the greater curvature of the upper gastric body, and a biopsy specimen showed a well to poorly differentiated adenocarcinoma. Following successful laparoscopic total gastrectomy, histopathological examination revealed an intramucosal adenocarcinoma arising in GHIP.

LGR5 expression and clinicopathological features of the invasive front in the fat infiltration area of pancreatic cancer.

BACKGROUND: Leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5) is a strong cancer stem cell marker in colorectal cancer; however, there are many unclear aspects of LGR5 expression in pancreatic cancer. It has been reported that the interaction between tumor cells and stroma at the fat infiltration site has a significant effect on pancreatic cancer prognosis. Therefore, we report a clinicopathological study of LGR5 expression at the fat invasion front in pancreatic cancer. METHODS: LGR5 expression was analyzed in 40 pancreatic ductal adenocarcinoma cases with RNAscope, which is a newly developed high-sensitivity in situ hybridization method. Epithelial-mesenchymal transition (EMT) was analyzed by the expression of E-cadherin and vimentin via immunohistochemistry. RESULTS: LGR5-positive dots were identified in all cases, especially with glandular formation. In the fat invasion front, a high histological grade showed significantly reduced LGR5 expression compared with a low histological grade (p=0.0126). LGR5 expression was significantly higher in the non-EMT phenotype group than in EMT phenotype group (p=0.0003). Additionally, LGR5 expression was significantly lower in cases with high vascular invasion than in those with low vascular invasion (p=0.0244). CONCLUSIONS: These findings suggest that decreased LGR5 expression in the fat invasion front is associated with more aggressive biological behavior in pancreatic ductal adenocarcinoma, with higher tumor grade, EMT phenotype, and higher vascular invasion.

LGR5-Expressing Cells in the Healing Process of Post-ESD Ulcers in Gastric Corpus.

BACKGROUND: LGR5 is a promising stem cell marker in gastric pylorus, but there are few reports on its expression in human gastric corpus. AIMS: To investigate the involvement of LGR5 expression in gastric corpus ulcer regeneration in humans. METHODS: LGR5 expression was analyzed in five post-ESD ulcers during the healing process of regenerating epithelial cells of the gastric corpus. LGR5 expression was detected by mRNA in situ hybridization using an RNA scope kit. Immunohistochemistry of MUC6, HIK1083, and pepsinogen 1 (PG1) was performed to identify cell differentiation. RESULTS: We defined MUC6+/HIK1083-/PG1-, MUC6+/HIK1083+/PG1-, MUC6+/HIK1083+/PG1+, MUC6+/HIK1083-/PG1+, and MUC6-/HIK1083-/PG1+cells as pseudopyloric mucosa (PPM) phase 1 (PPM1), PPM phase 2 (PPM2), PPM phase 3 (PPM3), immature chief cells (ICC), and mature chief cells (MCC) in order from the ulcer center, respectively. In the regenerated mucosa around post-ESD ulcers, LGR5 expression was observed throughout the gland in PPM1-PPM3, but it was limited to the bottom of the gland in ICC and MCC. Furthermore, LGR5 expression was not identified in the normal gastric corpus. The H-score of PPM2 was significantly higher than that of PPM3 (P = 0.0313). The H-score of PPM3 was significantly higher than that of ICC (P = 0.0313). The LGR5 H-score was higher at the immature stage, which decreased gradually with progression of the differentiation stage. CONCLUSIONS: LGR5 expression appears to contribute to mucosal regeneration in the human gastric corpus. The application of LGR5 expression analysis to mucosal regeneration and fundic gland-type gastric tumors is expected.