Does the immune system protect against cancer?
Dr. Anthony L. Komaroff, MD , Internal Medicine, answered The immune system is only moderately effective in fighting cancer. That's because cancer cells are essentially modified "self" cells. That means the immune system usually doesn't recognize them as harmful. The immune response is triggered only in certain types of cancer -- when cancer cells become so highly abnormal that they are recognizable as "nonself" cells. Sometimes these abnormalities involve changes in proteins made in the cancer cell. When these proteins appear on the cell surface via the major histocompatibility complex (MHC) molecule, the immune system recognizes them as antigens and responds accordingly. But even then, the immune system must race to keep up with the rapidly dividing cancer cells. One reason cancer cells are difficult to recognize is that they "hide" by removing from their surface the chemical ID that says something is wrong. Even in that case, natural kill...