Correlation between cyclooxygenase-2, proliferative activity, and mucin phenotype in human advanced gastric cancer

Recent studies have suggested that nonsteroidal anti-inflammatory drugs (NSAIDs) reduce the risk of gastrointestinal cancer, and that cyclooxygenase-2 (COX-2) may be a target enzyme for the prevention or regression of cancer by the use of NSAIDs. Mucin histochemistry has made possible a clear distinction between the differentiated characteristics of gastrointestinal epithelial cells, and the possibility that phenotypic shifts from gastric- to intestinal-type in gastric carcinoma progression has been suggested. To evaluate the role of COX-2 in gastric cancer progression, we immunohistochemically investigated COX-2 expression, and examined its relationship to proliferative activity, mucin phenotype, and clinicopathological parameters in human advanced gastric carcinomas.

Forty-five surgical specimens of advanced gastric carcinomas (invaded the muscularis propria or subserosa) were examined. Immunohistochemical staining was performed with monoclonal antibodies against COX-2, Ki-67, CD10 (brush border), MUC-2 (goblet-cell mucin), MUC-5AC (gastric foveolar mucin), and MUC-6 (pyloric mucin). COX-2 expression was scored by the percentage of COX-2-positive neoplastic cells, and proliferative activity was assessed by the Ki-67 labeling index at the deepest area of invasion. The mucin phenotype of the carcinomas was classified into three categories; gastric, intestinal, and unclassified.

COX-2 staining was restricted to the cytoplasm, not only in cancer cells but also in intestinal metaplasia and some inflammatory cells and COX-2 expression in cancer cells varied greatly, but the staining in some samples was preferentially found at the invasive front. COX-2 positivity was found to correlate with Ki-67 labeling. The mean COX-2 scores were 2.29%, 2.71%, and 2.75%; and the Ki-67 labeling indices were 23.6%, 40.6%, and 56.5%, in gastric-, intestinal-, and unclassified- type carcinomas, respectively.

A close relationship between COX-2 expression and proliferative activity was confirmed in the deepest areas of advanced gastric carcinoma, and the proliferative activity increased from gastric- to intestinal- and to unclassified- type gastric carcinoma, suggesting a role for COX-2 expression and differences in biological behavior according to mucin phenotype expression during gastric cancer progression.