Monoclonal antibody drugs for cancer: How they work

If you're considering monoclonal antibody therapy as part of your cancer treatment, learn about these drugs and carefully weigh the benefits against the potential side effects.

By Mayo Clinic Staff

Monoclonal antibody drugs are a relatively new innovation in cancer treatment. While several monoclonal antibody drugs are available for treating certain cancers, the best way to use these new drugs isn't always clear.

If you and your doctor are considering using a monoclonal antibody as part of your cancer treatment, find out what to expect from this therapy. Together you and your doctor can decide whether a monoclonal antibody treatment may be right for you.

What is a monoclonal antibody?

A monoclonal antibody is a laboratory-produced molecule that's carefully engineered to attach to specific defects in your cancer cells. Monoclonal antibodies mimic the antibodies your body naturally produces as part of your immune system's response to germs, vaccines and other invaders.

How do monoclonal antibody drugs work?

When a monoclonal antibody attaches to a cancer cell, it can:

  • Make the cancer cell more visible to the immune system. The immune system attacks foreign invaders in your body, but it doesn't always recognize cancer cells as enemies. A monoclonal antibody can be directed to attach to certain parts of a cancer cell. In this way, the antibody marks the cancer cell and makes it easier for the immune system to find.

    The monoclonal antibody drug rituximab (Rituxan) attaches to a specific protein (CD20) found only on B cells, one type of white blood cell. Certain types of lymphomas arise from these same B cells. When rituximab attaches to this protein on the B cells, it makes the cells more visible to the immune system, which can then attack.

    Rituximab lowers the number of B cells, including your healthy B cells, but your body produces new healthy B cells to replace these. The cancerous B cells are less likely to recur.

  • Block growth signals. Chemicals called growth factors attach to receptors on the surface of normal cells and cancer cells, signaling the cells to grow. Certain cancer cells make extra copies of the growth factor receptor.

    Extra growth factor receptors allow cancer cells to grow faster than the normal cells. Monoclonal antibodies can block these receptors and prevent the growth signal from getting through.

    Cetuximab (Erbitux), a monoclonal antibody approved to treat colon cancer and head and neck cancers, attaches to receptors on cancer cells that accept a certain growth signal (epidermal growth factor). Blocking this signal from reaching its target on the cancer cells may slow or stop the cancer from growing.

  • Stop new blood vessels from forming. Cancer cells rely on blood vessels to bring them the oxygen and nutrients they need to grow. To attract blood vessels, cancer cells send out growth signals.

    Monoclonal antibodies that block these growth signals may help prevent a tumor from developing a blood supply so that it remains small. Or in the case of a tumor with an already-established network of blood vessels, blocking the growth signals could cause the blood vessels to die and the tumor to shrink.

    The monoclonal antibody bevacizumab (Avastin) targets a growth signal called vascular endothelial growth factor (VEGF) that cancer cells send out to attract new blood vessels. Bevacizumab intercepts a tumor's VEGF signals and stops them from connecting with their targets.

  • Deliver radiation to cancer cells. By combining a radioactive particle with a monoclonal antibody, doctors can deliver radiation directly to the cancer cells. This way, most of the surrounding healthy cells aren't damaged.

    Radiation-linked monoclonal antibodies deliver a low level of radiation over a longer period of time, which researchers believe is as effective as the more conventional high-dose external beam radiation.

    Ibritumomab (Zevalin), approved for non-Hodgkin's lymphoma, combines a monoclonal antibody with radioactive particles. The ibritumomab monoclonal antibody attaches to receptors on cancerous blood cells and delivers the radiation.

  • Deliver chemotherapy to cancer cells. By combining chemotherapy drugs with a monoclonal antibody, doctors can deliver chemotherapy directly to the cancer cells.

    Ado-trastuzumab emtansine (Kadcyla) is one such drug approved to treat HER2-positive breast cancer. Ado-trastuzumab emtansine contains an antibody that attaches to the HER2 receptors on the breast cancer cells. The cancer cells then ingest the antibody, which releases a few molecules of chemotherapy.

    The chemotherapy only damages the cancer cells, leaving the surrounding healthy cells undamaged.

A number of monoclonal antibody drugs are available to treat various types of cancer. Clinical trials are studying monoclonal antibody drugs in treating nearly every type of cancer.

Feb. 07, 2014 See more In-depth