What is antibody therapy for cancer?

Targeted Rx. Some tumor cells have markers on their surface and are susceptible to damage by antibodies directed at that marker(s). In some lymphomas antibodies directed at markers present on normal cells are also effective. Usually these are monoclonal antibodies that have been specifically designed for use in humans.
Good targets. Cancer cells "look" different than normal cells; in other words, they display different proteins on their outside compared to normal cells. Antibodies latch onto proteins and can prevent those proteins from functioning, or they can attract the immune system to kill those cancer cells. So that's a quick overview of how antibody therapy can be used to treat cancer.
A great tool. Monoclonal antibodies are anticancer agents designed to bind to a unique protein (the antigen) on cancer cells. Ideally, this antigen is found only on the cancer cells, so our therapy is able to target the cancer cells while causing minimal harm, hence side effects, to normal tissues.