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Immunotherapy for Colorectal Cancer

Immunotherapy is a type of treatment that uses the body's own immune system to fight cancer. The therapy mainly consists of stimulating the immune system to help it do its job more effectively. Immunotherapy is a fairly new way to fight colorectal cancer. Many of these treatments are still in clinical trials.

Types of Immunotherapy

Biological Response Modifiers. These substances do not directly destroy the cancer, but they are able to trigger the immune system to indirectly affect tumors. Biological response modifiers include cytokines (chemicals produced by cells to instruct other cells) such as interferons and interleukins. This strategy involves giving larger amounts of these substances by injection or infusion in the hope of stimulating the cells of the immune system to act more effectively.

Colony-Stimulating Factors. These are substances that stimulate the production of bone marrow cells (the soft, sponge-like material found inside bones), which include both red and white blood cells and platelets. White blood cells fight infection; red blood cells carry oxygen to and carbon dioxide from organs and tissues; and platelets are cell fragments that help the blood to clot. Often, other cancer treatments cause decreases in these cells. Thus, colony-stimulating factors do not directly affect tumors, but they can help support the immune system during cancer treatment.

Tumor Vaccines. Researchers are developing vaccines that may encourage the immune system to better recognize cancer cells. These would, in theory, work in a similar way as vaccines for measles, mumps, and other infections. The difference in cancer treatment is that vaccines are used after someone has cancer, and not to prevent the disease. The vaccines would be given to prevent the cancer from returning or to get the body to reject tumor lumps. This is much more difficult than preventing a viral infection. The use of tumor vaccines continues to be studied in clinical trials.

Monoclonal Antibodies. These are substances produced in the lab that can locate and bind to cancer cells wherever they are in the body. These antibodies can be used to see where the tumor is in the body (detection of cancer), or as therapy to deliver drugs, toxins, or radioactive material directly to a tumor.

In February 2004, the FDA approved the first monoclonal antibody to treat metastatic colorectal cancer, Erbitux (cetuximab).

Also in February 2004, the FDA approved another first-of-its-kind monoclonal antibody called Avastin (bevacizumab). This drug works by shutting down a process called angiogenesis -- the process whereby tumors grow new blood vessels to help them receive the nutrients needed to survive. It's approved to treat advanced colorectal cancer that has spread to other organs.

In March of 2007 the FDA approved the drug Vectibix (panitumumab), which is similar to Erbitux for treating colorectal cancer that has spread.

The drugs cetuximab and panitumumab must be used in patients who do not have a mutation of a gene in their colon cancer known as K-ras. If this gene is present these drugs won’t work. Individuals with advanced colon cancer should routinely be checked for K-ras.

Bevacizumab attacks the blood supply of the cancer. Currently, doctors can't predict which patients who will respond best to it.

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