CP-675,206 is a fully human monoclonal antibody (mAb). It binds to the CTLA4 molecule, which is expressed on the surface of activated T lymphocytes. CP-675,206 is thought to stimulate patients' immune systems to attack their tumors. CP-675,206 is not expected to have a direct effect on tumor cells. CP-675,206 been shown to induce durable tumor responses in patients with metastatic melanoma in Phase 1 and Phase 2 clinical studies.