Background: Although almost all cases of gastric cancer are caused by Helicobacter pylori (HP) infection, there are some rare exceptions. Furthermore, the clinicopathological characteristics of gastric cancer may differ depending on HP infection status. This study aimed to determine the clinicopathological characteristics of undifferentiated-type gastric cancer (UD-GC) according to HP status.Methods: The study involved 83 patients with UD-GC who were selected from 1559 patients with gastric

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... er who underwent endoscopic resection at our hospital and whose HP infection status was confirmed. Clinicopathological characteristics were evaluated according to HP status (eradicated, n=28; infected, n=32; not infected, n=23).Results: In patients without HP infection, UD-GCs were <20 mm and intramucosal with no vascular invasion. In patients with eradicated HP, there was no correlation between development of UD-GC and time since eradication. Furthermore, 75% of patients with a tumor detected ≥5 years after eradication had undergone yearly endoscopy. Submucosal or deeper invasion was observed in 50% of patients and vascular invasion in 75% of patients whose UD-GC was detected ≥10 years after eradication. The proportion of patients with UD-GC and submucosal or deeper invasion was zero in the group without HP infection, 14.3% in the group with eradicated HP, and 10.5% in the HP-infected group.Conclusion: The clinicopathological characteristics of UD-GC were similar between HP-infected patients and HP-eradicated patients. Patients with eradicated HP whose UD-GC developed long after eradication had high rates of vascular and submucosal invasion. In contrast, UD-GC was curable by endoscopic resection in all patients without HP infection.