The active ingredient in a drug that is used to treat the symptoms of rheumatoid arthritis and is being studied in the prevention and treatment of some types of skin cancer. It blocks substances that cause inflammation and pain. It may also prevent the growth of new blood vessels that tumors need to grow. It is a type of cyclooxygenase inhibitor, a type of nonsteroidal anti-inflammatory drug (NSAID), and a type of antiangiogenesis agent.