A woman with breast cancer is treated with a monoclonal antibody to HER2. This is an example of

• A. a cancer vaccine.
• B. an immunotoxin.
• C. active immunotherapy.
• D. passive immunotherapy.

Answer: (D)

The main idea here is passive immunotherapy. Monoclonal antibodies given to a patient are preformed immune proteins that recognize a specific tumor antigen (HER2) and act right away to attack cancer cells, without the patient's own immune system having to generate a response. That immediate, externally supplied supply of antibodies defines passive immunotherapy.

Why the others don’t fit: a cancer vaccine aims to stimulate the patient’s own immune system to produce a response against cancer antigens, which is active immunotherapy. An immunotoxin would involve an antibody linked to a toxin to kill cells, which isn’t described here. Active immunotherapy and cancer vaccines require the body to mount a response, whereas giving a monoclonal antibody provides that response directly.