Monoclonal antibodies are used to treat many diseases, including some types of cancer. To make a monoclonal antibody, researchers have to identify the right antigen to attack. Finding the right antigens for cancer cells is not always easy, and so far mAbs have proven to be more useful against some cancers than others. Some monoclonal antibodies act like immunotherapy because they make the immune system respond better to allow the body to find and attack cancer cells more effectively.