Co-expression of osteopontin and CD44v9 in gastric cancer

We have examined the expression of osteopontin (OPN) in 40 human primary gastric carcinoma tissues, 5 metastatic foci (lymph nodes) and corresponding normal mucosas. Twenty-nine of 40 primary tumors (72.5%) and 3 of 5 lymph node metastases (60%) overexpressed OPN mRNA in comparison with those of the corresponding normal mucosa. The incidence as well as relative expression level of OPN mRNA was higher in well differentiated gastric cancers than poorly differentiated ones. Moreover, increased OPN mRNA expression in primary tumor specimens was observed along with the advancement of the clinico-pathological stage. Using in situ hybridization (ISH) analysis, not only inflammatory cells in tumor stroma but also tumor cells showed positive signals for OPN mRNA. By immunohistochemistry, co-immunoreaction of OPN and CD44v9 in tumor cells obviously correlated with the degree of lymphatic vessel invasion or long distant lymph node metastases in poorly differentiated gastric cancer. Interestingly, strong co-immunoreaction of OPN and CD44v9 of tumor cells was concommitant with cluster formation in the lymphatic vessels. Our results suggest that overexpression of OPN correlated with the progression of human gastric carcinoma. Especially in CD44-bearing poorly differentiated gastric cancer, interaction between OPN and CD44 may parallel lymphogenous metastasis.