Monoclonal antibodies

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was updated on July 5, 2022.

Given intravenously (through a vein), monoclonal antibodies are engineered molecules that are designed to attack specific features found on cancer cells.

The generic names of many monoclonal antibody drugs end in the letters “mab,” like trastuzumab or bevacizumab.

What do monoclonal antibodies do?

Monoclonal antibodies may be used in two ways:

  • Alone to destroy cancer cells 
  • As carriers of other substances for treatment or diagnostic purposes

As carriers, for example, monoclonal antibodies may deliver high concentrations of chemotherapy directly to the tumor cells. Or they may carry radioactive substances to locate previously undetected metastases (cancer cells that grow outside of the cancer’s original location). These approaches may be less toxic and produce better results than conventional chemotherapy or radiation therapy because they reduce the delivery of harmful agents to normal tissue.

How do monoclonal antibodies work?

Monoclonal antibody drugs are designed to work in several ways.

Immune system support: Some monoclonal antibodies help refocus the immune system to attack cancer cells. For example, checkpoint inhibitors block proteins that stop the immune system from working properly so that it may focus more fully on the cancer cells. Other monoclonal antibody drugs rally T-cells to kill cancer cells.

Cancer cell signal blockers: Some monoclonal antibodies block cancer cell signals to divide and conquer. Anti-angiogenic monoclonal antibody drugs block signals telling cancer cells to develop a blood supply, effectively starving them.

Direct delivery of chemotherapy and radiation therapy: Other types of monoclonal antibodies deliver chemotherapy or radiation therapy directly to cancer cells.

Which side effects may monoclonal antibodies cause?

Like all medications, monoclonal antibodies may produce some side effects. However, they tend to cause fewer and less severe side effects than chemotherapy. Potential side effects may include:

  • Allergic reactions (especially early on)
  • Fever
  • Chills
  • Headaches
  • Weakness
  • Nausea
  • Vomiting
  • Diarrhea
  • Low blood pressure
  • Rashes

Sometimes, these side effects relate directly to what the drug targets. Avastin® (bevacizumab), for example, targets vascular endothelial growth factor (or VEGF), which plays a role in forming blood vessels. As a result, it may cause high blood pressure, bleeding, poor wound healing, blood clots and kidney damage. Erbitux® (cetuximab) targets the epidermal growth factor receptor (or EGFR), which plays a role in cell division and survival. Serious rashes may result.

How are monoclonal antibody drugs chosen?

Before determining whether a monoclonal antibody is an appropriate treatment, an oncologist may order tests to help determine which protein may be driving the cancer’s behavior. These tests may include advanced genomic testing, genetic testing or an examination by a pathologist.

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