What Is Monoclonal Antibody Therapy?

Monoclonal antibody therapy is a targeted cancer therapy. It is sometimes called immunotherapy. While surgery, chemotherapy, and radiation therapy remain important treatment options for colon cancer, monoclonal antibody therapy is becoming more widely available for use. The most common monoclonal antibody therapies for managing colon cancer are Bevacizumab (Avastin), Cetuximab (Erbitux), and Panitumumab (Vectibix). 

What Are Monoclonal Antibodies?

Monoclonal antibodies are proteins that are made in a laboratory. These proteins are designed to attach to areas on the surface of cancer cells and interfere with their growth and spread. Monoclonal antibodies are similar to the antibodies your body naturally produces when you are exposed to bacteria or viruses, such as a cold or the flu (influenza).

How Do Monoclonal Antibodies Work?

The cells in our body, including cancer cells, have areas on their surface called receptors. These receptors help control how our cells grow, stop growing, or do any of the things cells normally do. If the right protein comes along and attaches (binds) to a receptor on a cell, this triggers the cell to respond.

A good way to think of receptors and their binding proteins is to think of a lock and key. A lock won't open without the right key. In the same way, a receptor won't trigger a cell to grow, divide, or respond unless the right "key" to that receptor attaches first. Monoclonal antibodies are "keys" that are specially designed to attach to receptors on cancer cells and block their function or elicit an immune response.

Examples of Monoclonal Antibody Therapies

Epidermal growth factor receptors (EGFRs) are one example of receptors that monoclonal antibodies target. EGFRs are present on normal cells and cancer cells, but with cancer cells, these receptors aren't normal. There may be too many EGFRs or they may be damaged or changed (mutated) in a way that allows them to over-respond to growth signals. This makes the cancer cells grow too fast or grow in places they shouldn't grow.

The monoclonal antibody therapies Cetuximab (Erbitux) and Panitumumab (Vectibix) specifically attach to the EGFRs that are found on cancer cells. When they attach to EGFRs, they block the growth signals that your body normally produces from reaching the cancer cells. This slows or stops cancer growth.

Thinking of the lock and key analogy, you can picture that Cetuximab and Panitumumab work as if someone stuck gum in the lock. The key can't go in and the door can't be opened because the cancer cell receptors are already "gummed up" by the monoclonal antibodies. This means the cancer cells no longer receive the growth signals they need to continue growing and spreading.

Conjugated Monoclonal Antibodies

Beyond just gumming up the works of the tumor cell, monoclonal antibodies can be joined to a chemotherapy drug or a radioactive particle (radioimmunotherapy) so they take the treatment action right to cancer and not to normal cells. This is being used with some forms of lymphoma and breast cancer and drugs may become available to treat other forms of cancer.

Side Effects of Monoclonal Antibody Therapy

For many people, the side effects of monoclonal antibody therapy are milder than chemotherapy and resemble an allergic type of reaction. Some of the more common side effects of monoclonal antibody therapy include:

• Skin rashes
• Skin itching or hives
• Flu-like symptoms such as fever, chills, muscle aches, fatigue, and headache
• Diarrhea
• Nausea and vomiting
• Low blood pressure

Some people do have serious reactions to monoclonal antibody therapy. More serious side effects that may cause your healthcare provider to stop monoclonal antibody therapy include:

• Very low blood counts
• Heart problems including irregular heartbeat, heart failure, and an increased risk of heart attack
• Low levels of magnesium, potassium, or calcium in your blood, which can cause serious health problems
• Serious skin rashes that lead to infections
• Bleeding problems
• Immediate reactions to the infusion including shortness of breath, wheezing, hoarseness, fainting, dizziness, blurred vision, nausea, or chest pain or pressure

Fortunately, when serious reactions occur, they often happen immediately, when you are receiving the medication at your cancer care clinic. This means your healthcare provider and nurse will be monitoring you and will be able to stop the infusion if needed and give you immediate medical attention.

Managing Monoclonal Antibody Treatment Side Effects

The two most important things you can do to manage side effects of monoclonal antibody therapy are to:

1. Take all of your medications as prescribed, because it’s easier to prevent side effects than to treat them once they occur.
2. Keep the lines of communication open with your medical team. What works to manage side effects for one person may not work for you. Talk to your healthcare provider or nurse about options to help you get through treatment with minimum side effects.

Don’t accept that feeling badly is a natural part of cancer treatment. There may be a way for your medical team to better manage your side effects. If you need help, ask for it. And always, if you have any questions about side effects, call your medical team right away.