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.

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.

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.

Monoclonal antibodies are administered through a vein (intravenously). How often you undergo monoclonal antibody treatment depends on your cancer and what drug you're receiving.

Some monoclonal antibody drugs may be used in combination with other treatments, such as chemotherapy and hormone therapy. Others are administered alone.

Monoclonal antibody drugs were initially used to treat advanced cancers that hadn't responded to chemotherapy or cancers that had returned despite treatment. However, because these treatments have proved to be effective, certain monoclonal antibody treatments are being used earlier in the course of the disease.

For instance, rituximab can be used as an initial treatment in some types of non-Hodgkin's lymphoma, and trastuzumab (Herceptin) is used in the treatment of some forms of early breast cancer.

Many of the monoclonal antibody therapies are still considered experimental. For this reason, these treatments are usually reserved for advanced cancers that aren't responding to standard, proven treatments.

In general, monoclonal antibody treatment carries fewer side effects than do traditional chemotherapy treatments.

However, monoclonal antibody treatment for cancer may cause side effects, some of which, though rare, can be very serious. Talk to your doctor about what side effects are associated with the particular drug you're receiving.

Common side effects

In general, the more common side effects caused by monoclonal antibody drugs include:

  • Allergic reactions, such as hives or itching
  • Flu-like signs and symptoms, including chills, fatigue, fever, and muscle aches and pains
  • Nausea
  • Diarrhea
  • Skin rashes

Serious side effects

Serious, but rare, side effects of monoclonal antibody therapy may include:

  • Infusion reactions. Severe allergy-like reactions can occur and, in very few cases, lead to death. You may receive medicine to block an allergic reaction before you begin monoclonal antibody treatment. Infusion reactions usually occur while treatment is being administered or soon after, so your health care team will watch you closely for a reaction.
  • Dangerously low blood cell counts. Low levels of red blood cells, white blood cells and platelets may lead to serious complications.
  • Heart problems. Certain monoclonal antibodies may cause heart problems, including heart failure and a small risk of heart attack.
  • Skin problems. Sores and rashes on your skin can lead to serious infections in some cases. Serious sores can also occur on the tissue that lines your cheeks and gums (mucosa).
  • Bleeding. Some of the monoclonal antibody drugs are designed to stop cancer from forming new blood vessels. There have been reports that these medications can cause bleeding.

Discuss your cancer treatment options with your doctor. Together you can weigh the benefits and risks of each treatment and decide whether a monoclonal antibody treatment is right for you.

Questions to ask your doctor include:

  • Has the monoclonal antibody drug shown a clear benefit? Some monoclonal antibody drugs are approved for advanced cancer, though they haven't been shown to extend lives. Instead, some drugs are more likely to slow a cancer's growth or stop tumor growth temporarily.
  • What are the likely side effects of monoclonal antibody treatment? With your doctor, you can determine whether the potential side effects of treatment are worth the likely benefit.
  • How much will monoclonal antibody treatment cost? Monoclonal antibody drugs can cost thousands of dollars for each treatment. Insurance doesn't always cover these costs.
  • Is monoclonal antibody treatment available in a clinical trial? Clinical trials, which are studies of new treatments and new ways to use existing treatments, may be available to you. In a clinical trial, the cost of the monoclonal antibody drug may be paid for as a part of the study. Also, you may be able to try new monoclonal antibody drugs. Talk to your doctor about what clinical trials may be open to you.
Feb. 07, 2014