Objective - To determine whether cyclooxygenase-2 (COX-2) is expressed in benign or malignant canine uveal melanocytic neoplasms and whether expression correlates with malignancy. Sample Population - Tissue sections from 71 globes; 57 with benign (n = 15), malignant (34), or mixed (8) uveal melanocytic neoplasms; 10 with nonneoplastic disease; and 4 with no abnormalities. Procedures - Bleached sections from all globes and canine kidney were incubated with mouse monoclonal antibody directed against rat COX-2 protein or mouse antibody isotype control. Location, intensity, and percentage of immunolabeled cells were scored. Results - Expression of COX-2 was detected in all but 5 globes, all of which contained neoplasms. Expression of COX-2 was detected in regions infiltrated by neoplasia in 21 globes; however, definitive labeling of tumor cells was detected in only 2 of those. In the remaining 19 globes, COX-2 expression was detected in areas also labeled in globes without disease and globes with nonneoplastic disease, especially the aqueous outflow tract and ciliary body. However, only globes with uveal malignant melanomas had detectable COX-2 expression in the iris. Expression of COX-2 was detected in the ciliary body of more globes with uveal malignant melanoma (20/34) than in those without disease (1/4), with nonneoplastic disease (4/10), or with melanocytoma (3/15) or mixed neoplasms (3/8). Conclusions and Clinical Relevance - Canine globes with uveal melanocytic neoplasia appeared to express COX-2 in similar sites and with similar intensity as globes without neoplasia. Differentiation of benign from malignant canine uveal melanocytic neoplasms was not possible.
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