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Background: In Western countries, gastric cancer (GC) is diagnosed when there is histological evidence of invasion into the lamina propria or beyond the submucosa. In Japan and some other countries, however, diagnosis of GC is based on the degree of structural and cytological abnormality of tumor glands. The aim of the present study was to compare the accuracy of the Western and Japanese criteria for diagnosis of GC. Methods: The study included 233 consecutive patients with a postoperative diagnosis of submucosal invasive GC who underwent gastrectomy or endoscopic submucosal dissection. All pretreatment biopsy specimens were independently reviewed by two experts in gastrointestinal pathology employing both the Western and Japanese diagnostic criteria. Diagnostic agreement between pretreatment biopsy specimens and the corresponding resected specimens was evaluated, together with the interobserver agreement for each of the criteria. Results: On the basis of the Western and Japanese criteria, the pretreatment biopsy diagnosis was noncancerous (including dysplasia) in 44 lesions and 1 lesion, respectively. Diagnostic accuracy based on biopsy was 81.1 % for the Western criteria and 99.5 % for the Japanese criteria ( P < 0.001). Interobserver agreement based on the Western and Japanese criteria was 73.8 % and 96.5 %, respectively ( P < 0.001). Invasion into the submucosa was detected by biopsy in only 25 cases. Conclusions: The Japanese criteria are significantly more accurate for pretreatment biopsy diagnosis of GC. The Western criteria could lead to underdiagnosis of a lesion as high-grade dysplasia, even if submucosal invasive cancer is present. [ABSTRACT FROM AUTHOR]