An immunohistochemical study of cyclooxygenase (COX)-2 expression in endocrine tumors of the pancreas.

Cyclooxygenase (COX) is a key rate-limiting enzyme in prostaglandin biosynthesis. There are two isoforms of COX, referred to as COX-1 and COX-2. COX-2, an inducible form of COX, is found to be overexpressed in various neoplasms and is believed to play an important role in tumorigenesis and tumor development. In this study, we investigated expression of the COX-2 protein in human endocrine tumors of the pancreas (N=23; 6 insulinomas, one glucagnoma, 2 gastrinomas, and 14 non-functioning tumors) using immunohistochemistry. Strong COX-2 expression was confirmed in normal islet tissue as previously reported. COX-2 immunoreactivity was detected in 65% (15 out of 23) of these tumors with a moderate to strong intensity. In all nine functioning tumors, COX-2 expressions were preserved with the weak or strong intensity. In contrast, COX-2 was present in 6 out of 14 nonfunctioning tumors. The correlation between COX-2 expression and their function was significant (p<0.05). We found that expression of this enzyme was detected in 11 out of 15 benign tumors and in 4 out of 8 malignant tumors, respectively. Our results suggest that COX-2 may play an important role in the endocrine function of islet tumors. Additionally, malignancy was not related to COX-2 expression.