man-made antibodies that are designed to lock onto certain antigens (substances that can be recognized by the immune system). Monoclonal antibodies have several uses in diagnosing and treating cancer. They are often used to help detect and classify cancer cells under a microscope. “Naked” monoclonal antibodies can attach to parts of cancer cells to either affect the cells directly or mark the cells so they can be found and attacked by the immune system. Other monoclonal antibodies are attached to chemotherapy drugs or radioactive substances and deliver these treatments directly to the cancer cells, killing them with little risk of harming healthy tissue. Research is still going on to learn more ways they can be used to find and treat cancer. See also antibody, antigen, chemotherapy, imaging tests, immunocytochemistry.