Gastric cancer is a major cause of cancer-related death worldwide. Its incidence and mortality have been decreasing due to a prevalence of refrigerator for food storage, leading to intake of fewer salted and smoked food, and a decline in Helicobacter pylori infection [1]. However, gastric cancer is still responsible for estimated 1,089,103 new cases ranking fifth and 768,793 deaths ranking fourth globally in 2020 [2]. As of 2023, the 5-year relative survival rate is 72% for the localized stage, 33% for the regional stage, 6% for the distant stage, and 33% for all stages combined [3].

Early-stage gastric cancer, for which endoscopic resection was not indicated or actually failed in complete resection, and resectable locally advanced gastric cancer are usually subjected to gastrectomy. Pathologists appraise resected specimens in terms of histopathologic tumor-related factors, such as tumor site, tumor size, histological subtype, differentiation grade, depth of invasion, invasion pattern, desmoplasia or degree of stromal reaction, lymphovascular invasion, lymph node metastasis and resection margin status in the routine practice [[4], [5], [6], [7], [8]] and report the results to clinicians for subsequent treatments. Among these factors, depth of invasion (T), lymph node metastasis (N) and distant metastasis (M) have been accepted as the most powerful indicators of prognosis. Meanwhile, the prognostic relevance of other histopathologic factors has not been consistently recognized. Although histological type is always described in the pathology report and pathologists often make a substantial effort to determine it, the prognostic relevance of histological type and resulting differentiation grade has been controversial thus far.

More than 90% of gastric cancer is gastric adenocarcinoma (GAC). The purpose of this study was to elucidate the prognostic relevance of histological subtype and differentiation grade of GAC after curative resection. In addition, we discussed the criteria for additional gastrectomy after endoscopic treatment for early-stage GAC based on the data obtained in this study.