What Are Monoclonal Antibodies?
Antibodies are substances produced by the immune system in response to foreign invaders such as bacteria or viruses. Antibodies can stick to the invader and help destroy it. Monoclonal antibodies are a specific type of antibody, created in a lab to find and destroy a particular target -- in this case, cancer. Because of their precision, it is hoped that treatment of a tumor with a monoclonal antibody will be more specific than chemotherapy drugs and therefore have fewer side effects.
Bevacizumab (Avastin) was one of the first of its kind of monoclonal antibodies that shuts down a process called angiogenesis -- the process whereby tumors grow new blood vessels to help them receive the nutrients needed to survive. The class of drugs is called angiogenesis inhibitors or anti-angiogenic drugs.
Specifically, Avastin stops the action of a substance released by tumors called vascular endothelial growth factor, or VEGF. VEGF binds to certain cells to stimulate new blood vessel formation. Interfering with tumor blood vessels might slow their growth. Avastin is an approved drug to treat advanced colon or rectal cancer that has spread to other organs (metastasized). The drug is not a cure, but studies show that the use of Avastin along with chemotherapy increased survival of patients with metastatic colon cancer by five months.
Ramucirumab (Cyramza) and ziv-aflibercept (Zaltrap) are newer angiogenesis inhibitors that also work by binding to VEGF receptors.
How Is Avastin Given?
Avastin is an injection that is given along with the chemotherapy. The injection is given in a vein (intravenously or IV) every two or three weeks.
Studies show that the drug enhances the effects of chemotherapy, but it does not appear to be effective when given alone in patients with colorectal cancer.
What Are the Possible Side Effects of Avastin?
Common side effects of Avastin include:
- Fatigue and weakness
- High blood pressure
- Loss of appetite
Serious side effects of Avastin include:
- Holes in the colon requiring surgical repair
- Heart attack
- Chest pain
- Kidney damage causing increased protein in the urine
- Decreased ability of wounds to heal (so it shouldn't be used right after surgery)
- Bleeding or blood clotting problems
Cetuximab (Erbitux) and panitumumab (Vectibix)
Cetuximab (Erbitux) and panitumumab (Vectibix) are other monoclonal antibodies. These drugs slow cancer growth by targeting a protein found on the surface of some cells called the epidermal growth factor receptor (EGFR). EGFR plays a role in regulating cell growth and is present in about 75% of colon cancers.
Erbitux and Vectibix are believed to interfere with the growth of cancer cells by binding to EGFR so that the normal epidermal growth factors cannot bind and stimulate the cells to grow.
Erbitux and Vectibix are FDA-approved to treat colorectal cancers that have spread to other parts of the body (metastasized). Erbitux is administered intravenously weekly either alone or with a cancer chemotherapy drug called irinotecan (Camptosar).
Vectibix is also given intravenously but every other week and usually with certain combinations of chemotherapy. Before using these drugs, a special genetic mutation test needs to be done on the cancer to see if they will be effective.
What Are the Possible Side Effects of Erbitux and Vectibix?
Side effects Erbitux and Vectibix could include:
- Skin problems, like acne, rash, and dry skin; skin reactions may actually mean the drug is working against the cancer.
- Fatigue and weakness
- Abdominal pain
- Allergic reactions causing difficulty breathing and low blood pressure
- Reactions while the drug is being given