Cyclooxygenase-2 expression in human irradiated uveal melanomas

Abstract

Previous studies have shown that radiotherapy is a stimulus for cyclooxygenase-2 (COX-2) expression and that use of COX-2 inhibitors enhances the radio sensitivity of tumor cells. The objective of this study was to evaluate COX-2 expression, and its correlation with tumor regrowth after irradiation, in enucleated eyes with uveal melanomas. Fifteen tissue samples from patients who underwent enucleation after radiotherapy between 1988 and 2001 were used. Nine cases (60%) were enucleated because of tumor regrowth and six (40%) because of severe complications of radiotherapy. Specimens were immunostained for COX-2, and tumor cells were evaluated for specific cytoplasmic and granular immunostaining. COX-2 expression for these cases was compared with that in the previous study including 40 non-irradiated uveal melanoma cases. COX-2 expression was also correlated with tumor regrowth after radiotherapy. Two cases (13.3%) were positive and thirteen (86.7%) were negative for COX-2 expression. One of the positive cases had been enucleated because of tumor regrowth and one because of radiotherapy complications. There was no relationship between tumor regrowth and COX-2 expression. COX-2 expression was significantly lower in irradiated cases than in non-irradiated cases in the previous study (p<0.001). In contrast with studies showing an increase of COX-2 expression in other irradiated malignancies, irradiation was not a factor inducing COX-2 in uveal melanomas. Radiotherapy may, moreover, be a factor that reduces COX-2 expression in uveal melanomas.