Well-differentiated adenocarcinoma or dysplasia of the gastric epithelium: rationale for a new classification system.

BACKGROUND: Gastric neoplastic lesions labelled as high-grade adenoma/dysplasia by Western pathologists are often diagnosed as mucosal carcinoma by Japanese pathologists. We examined whether stratifying histological diagnoses by invasion status could increase the extent of agreement between Western and Japanese pathologists and could reduce the frequency of discrepant diagnoses between biopsy samples and corresponding resected specimens.
METHODS: Thirty-five histological slides of gastric lesions that had previously been individually reviewed by eight expert gastrointestinal pathologists from Japan, North America and Europe were reassessed by the same pathologists with particular attention to the aspect of invasion. Kappa statistics were used to determine the extent of agreement between Western and Japanese pathologists before and after reclassifying the diagnoses according to invasion status. Moreover, we examined the number of discrepant assessments regarding 14 lesions of which there were both biopsy specimens and resected specimens.
RESULTS: There was agreement between the Western and Japanese pathologists in only 11 (31%) of the 35 slides (kappa coefficient 0.15) when traditional diagnostic categories were used. However, after high-grade adenoma/dysplasia, noninvasive carcinoma and suspected carcinoma were grouped together, there was better agreement, namely in 22 (63%) of the slides (kappa coefficient 0.41). Moreover, such reclassification significantly reduced the number of discrepant diagnoses between biopsy and endoscopic mucosal resection specimens by three Western pathologists, from 19 (45%) of 42 assessments when high-grade adenoma/dysplasia was grouped together with low-grade adenoma/dysplasia, to 6 (14%) of 42 assessments when grouped with suspected and definite carcinoma.
CONCLUSIONS: To improve the international comparability of gastric histological diagnoses we recommend that high-grade adenoma/dysplasia, noninvasive carcinoma and suspicion of invasive carcinoma be grouped together as a single category of noninvasive high-grade epithelial neoplasia.