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Cyclooxygenase (COX)-2 is an inducible enzyme linked to tumor growth and angiogenesis. Its expression occurs in a wide range of preneoplastic and neoplastic conditions in humans, including colon and breast carcinomas. We evaluated the role of COX-2 as a mediator of angiogenesis in feline and canine invasive carcinomas (IMCs) and its role as a prognostic indicator. COX-2 expression was assessed in neoplastic samples and healthy mammary glands by immunohistochemistry, and related to the following clinicopathological parameters: age, tumor size, histologic type, tumor grading, vessel invasion, estrogen (ER) and progesterone receptor (PR) status, Ki-67, HER-2 overexpression, microvessel density (MVD), VEGF expression and overall survival (OS). In both species, COX-2 immunoreactivity was not observed in healthy tissues, whereas 96% of feline and 100% of canine invasive carcinomas scored positive. In queens, COX-2 overexpression was significantly correlated to ER-negative status (p=0.04) and to increased PR (p=0.038) expression, and angiogenesis assessed by VEGF expression (p=0.002). In bitches an increased COX-2 expression was significantly correlated to HER-2 overexpression (p=0.013) and to tumor dedifferentiation (p=0.03). In both species increased levels of COX-2 were correlated to poorer prognosis (p=0.03 in dogs and p=0.002 in cats). COX-2 is expressed in mammary tissues during tumorigenesis and its expression is associated with a poorer prognosis in bitches and queens. The correlation of COX-2 expression and angiogenesis provides support for a potential role of COX-2 inhibitors for the prevention and the treatment of feline IMCs via their anti-angiogenic properties. In the canine species, moreover, COX-2 may be important for mediating HER-2 induced mammary tumors.

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