Cyclooxygenase (COX) is a bifunctional enzyme that catalyzes the conversion of arachidonic acid to various prostaglandins. COX-2, which is well-known for its role in inflammation, also influences cell differentiation, replication, and carcinogenesis. Possible mechanisms for its role in tumor growth and metastasis include tumor angiogenesis, decreased apoptosis, increased metalloproteinase activity, and chronic inflammation. COX-2 has been implicated in the development and progression of several types of cancer in humans, and epidemiologic studies have linked long-term nonsteroidal antiinflammatory drug (NSAID) use with prevention of certain types of cancer in humans. In animals, there are few studies of COX-2 involvement in cancer and the role of NSAIDs in treatment or prevention of cancer. The most important question at this time is to determine which types of cancer result in overexpression of COX-2. Piroxicam, carprofen, and meloxicam are some of the COX inhibitors that have been studied for use in dogs with various tumors. However, predicting the effect of NSAIDs on tumor growth and determining an effective dose that avoids toxicity is difficult. Controlled clinical trials are needed to answer many questions.

COMMENTARY: Most veterinary pharmacies contain COX inhibitors that are used regularly for management of inflammation and pain. Despite encouraging news that they may also be effective against certain types of cancer, COX-inhibiting drugs should not indiscriminately be listed as chemotherapeutic agents. COX is only one of many abnormal pathways in which cancer cells may be involved, and COX-2 inhibitors are apparently only effective in certain types of cancer. Furthermore, predicting drug dose is not straightforward and toxicity is an issue

Cancer, cyclo-oxygenase and nonsteroidal anti-inflammatory drugs-Can we combine all three? Hayes A. VET COMP ONCOL 5:1-13, 2007.