Aberrant intracellular localization of RCAS1 is associated with tumor progression of gastric cancer

A novel tumor-associated antigen, RCAS1 (receptor-binding cancer antigen ex pressed on SiSo cells) is expressed at a high frequency in human uterine an d ovarian cancer cells as well as in other mammalian cancer cells. We inves tigated a relationship between RCAS1 expression and clinicopathological fea tures in gastric cancer. Immunohistochemically, RCAS1 was detected in 98.4% of gastric carcinomas. However, its expression was also observed in noncan cerous gastric epithelial cells including gastric adenomas (100%), gastric ulcers (66.7%) and normal gastric epithelia (100%). Striking difference was observed in the pattern of RCAS1 expression between benign and malignant c ells. In cases of normal gastric mucosae, gastric ulcers and gastric adenom as, RCAS1 was localized only in the perinuclear region of the mucosal epith elial cells (PN pattern), while, in most of gastric cancers (83.9%), it was detected diffusely in the cytoplasm and cell membranes of the tumor cells (DC pattern). In semi-quantitative RT-PCR analysis, RCAS1 mRNA levels in ga stric adenocarcinoma tissues were significantly higher than those in non-ne oplastic tissues (p=0.038). The PN pattern of RCAS1 expression frequently o bserved in well differentiated adenocarcinoma (25%) than in moderately diff erentiated adenocarcinoma (0%) (p=0.01). In addition, it is noteworthy that DC pattern of RCAS1 expression was more frequently recognized in carcinoma s which invaded beyond the submucosa (100%) compared to intramucosal carcin oma (67.7%) (p=0.0026). These findings suggest that altered intracellular d istribution of RCAS1 is strictly associated with tumor progression of gastr ic cancer and is a useful marker for the diagnosis and prognosis in gastric cancer.