PURPOSE:Cyclooxygenase‐2 is an important target for nonsteroidal anti‐inflammatory drugs in suppressing colorectal tumorigenesis. To evaluate the role of cyclooxygenase‐2 in sporadic colorectal adenoma, we correlated cyclooxygenase‐2 expression in adenomas with other adenoma characteristics.METHODS:Cyclooxygenase‐2 expression was evaluated immunohistochemically in 95 endoscopically resected colorectal adenomas.RESULTS:Cyclooxygenase‐2 was expressed mainly in the cytoplasm of adenoma cells, where it was seen in 74 percent (70/95) of adenomas. Expression was related significantly to grade of dysplasia (P< 0.001) and tumor size (P= 0.028). Multivariate logistic regression analysis showed cyclooxygenase‐2 expression in adenoma cells to be independently associated with grade of dysplasia (P= 0.001).CONCLUSION:Observed associations suggest that cyclooxygenase‐2 plays an important role in progression of the adenoma‐to‐carcinoma sequence.