Monoclonal antibodies work by which mechanism?

• A. acting on the DNA phase of a cancer cell
• B. binding to specific antigens on cancer cells inducing an immunologic response
• C. blocking the supply of blood to the tumor
• D. all of the above

Answer: (B)

Monoclonal antibodies act by recognizing and binding to a specific antigen on the surface of cancer cells. This binding flags the cancer cell for destruction by the immune system, such as through antibody-dependent cellular cytotoxicity or by activating the complement system, leading to tumor cell death. Some antibodies also block growth signals by preventing receptor activation, which can slow or stop tumor growth. The idea of acting on the DNA phase isn’t how these antibodies work, since they target surface antigens and immune-mediated or signaling effects rather than directly altering DNA. Blocking blood supply is not the defining mechanism for most monoclonal antibodies, even though anti-angiogenic antibodies exist, they don’t represent the central action of typical Mabs. So, binding to specific tumor antigens and triggering an immune response best explains their primary mechanism. For example, therapies like rituximab target a surface antigen on B cells and recruit immune cells to destroy them.