Immunohistochemical expression of cyclooxygenase-2 in normal, hyperplastic and neoplastic canine lymphoid tissues.

There is much interest in the potential use of selective inhibitors of cyclooxygenase (COX)-2 in combination with other cancer therapeutics. COX-2 is a key enzyme in prostaglandin synthesis and has been implicated in the pathogenesis of numerous canine and feline malignancies. There are few data on the potential role of COX-2 in the pathogenesis of canine lymphoma. The present study examined COX-2 expression in normal, hyperplastic and neoplastic canine lymphoid tissues. Immunohistochemical expression was evaluated in 12 samples of non-pathologically enlarged normal lymph nodes, 24 samples of hyperplastic lymph node and 44 samples of lymphoma (22 B-cell and 22 T-cell lymphomas). The labelling was scored semiquantitatively and a score of +2 or +3 was interpreted as overexpression. In hyperplastic lymph nodes only a few macrophages were COX-2-positive while six of the 44 lymphomas (13.6%; three B- and three T-cell lymphomas) overexpressed COX-2. These data provide a rationale for further investigation of COX-2 expression in canine lymphoma for prognostic, chemopreventive and chemotherapeutic purposes.