AIM:To systematically study the expression of carbonicanhydrase (CA) isozymes Ⅸ and Ⅻ in gastric tumors.METHODS:We analyzed a representative series ofspecimens from non-neoplastic gastric mucosa and fromvarious dysplastic and neoplastic gastric lesions for theexpression of CA Ⅸ and Ⅻ.Immunohistochemical stainingwas performed using isozyme-specific antibodies and biotin-streptavidin complex method.RESULTS:CA IX was highly expressed in the normal gastricmucosa and remained positive in many gastric tumors.Inadenomas,CA Ⅸ expression significantly decreased towardsthe high grade dysplasia.However,the expression resumedback to the normal level in well differentiated adenocarcinomas,while it again declined in carcinomas with less differentiation.In comparison,CA Ⅻ showed no or weak immunoreaction inthe normal gastric mucosa and was slightly increased in tumors.CONCLUSION:These results demonstrate that CA Ⅸexpression is sustained in several types of gastric tumors.The variations observed in the CA Ⅸ levels support the conceptthat gastric adenomas and carcinomas are distinct entitiesand do not represent progressive steps of a single pathway. AIM: To systematically study the expression of carbonicanhydrase (CA) isozymes Ⅸ and Ⅻ in gastric tumors. METHODS: We analyzed a representative series of specimens from non-neoplastic gastric mucosa and from various dysplastic and neoplastic gastric lesions for the expression of CA Ⅸ and I. Immunohistochemical staining was performed using isozyme-specific antibodies and biotin-streptavidin complex method .RESULTS: CA IX was highly expressed in the normal gastric mucosa and remained positive in many gastric tumors. Innadenomas, CA Ⅸ expression significantly decreased toward high-grade dysplasia. to the normal level in well differentiated adenocarcinomas, while it again declined in carcinomas with less differentiation.In contrast, CA Ⅻ showed no or weak immunoreaction inthe normal gastric mucosa and was slightly increased in tumors. CONCLUSION: These results demonstrate that CA Ⅸ expression is sustained in several types of gastric tumors. variations observed in the CA Ⅸ levels support the conceptthat gastric adenomas and carcinomas are distinct entities and do not represent progressive steps of a single pathway.