Which of the following is a monoclonal antibody used in cancer therapy?

• A. Etoposide
• B. Topotecan
• C. Rituximab
• D. Imatinib

Answer: (C)

Monoclonal antibodies are engineered immune proteins that bind to a single, specific target on cancer cells. Rituximab fits this role because it binds CD20, a protein on the surface of most B cells. By attaching to CD20, Rituximab flags these cells for destruction through immune mechanisms like antibody-dependent cellular cytotoxicity and complement activation, helping to kill malignant B cells. This targeted approach is different from traditional chemotherapies that broadly damage rapidly dividing cells (such as etoposide and topotecan) or from small-molecule inhibitors like imatinib, which block signaling inside cells rather than acting as antibodies. So Rituximab is the monoclonal antibody used in cancer therapy among the options.