An immunohistochemical study of ras oncoprotein expression in gastric carcinoma

Previous studies have shown that ras oncoprotein is overexpressed in gastric carcinoma. It is unsettled whether there is differential expression of this oncoprotein in the two major subtypes of gastric carcinoma--intestinal type and diffuse type.

Forty-four cases of gastric carcinomas (24 intestinal type, 18 diffuse type, and 2 mixed according to the Lauren classification) were analyzed for ras oncoprotein expression using commercially available antibodies in routinely formaldehyde-fixed, paraffin-embedded tissue sections.

Altogether, 13 cases stained unequivocally, and these appeared as granular cytoplasmic staining in tumor cells. Only five were intestinal-type carcinomas; the remaining eight were diffuse type and included two intramucosal carcinomas. When the comparison between the two subtypes was limited only to the poorly differentiated carcinomas, the difference was statistically significant (P < 0.05). ras Oncoprotein also was strongly expressed in normal duodenal mucosa as well as areas of gastric intestinal metaplasia.

These results suggest that the strong expression of ras oncoprotein in gastric intestinal metaplasia may be merely a reflection of metaplastic change to an intestinal epithelial phenotype. The differential expression of ras oncoprotein between diffuse-type and poorly differentiated intestinal-type gastric carcinoma implies that these are two distinct subtypes of gastric carcinoma.