Colorectal Cancer: Chemotherapy and Immunotherapy
What is chemotherapy?
Chemotherapy refers to drugs that kill cancer cells. Chemotherapy drugs can be given in several ways: intravenously via an injection or a pump, or by mouth as a pill. Each drug works against a specific cancer and is administered in specific doses and schedules. Chemotherapy may be recommended for advanced colorectal cancers, in which the cancer cells have spread to the lymph nodes (drainage nodules) or to other organs. The various situations where chemotherapy is used are:
Primary chemotherapy is used when the colorectal cancer has already spread (metastasized) to other organs like the liver or lungs. In this situation, since surgery usually cannot eliminate the cancer, the best approach is treatment with chemotherapy, which possibly can shrink the tumor nodules, relieve symptoms, and prolong life.
Neo-adjuvant chemotherapy is given before surgery for certain rectal cancers in order to shrink the tumor, allowing the surgeon to better remove it. In this situation, radiation is usually administered along with the chemotherapy.
When appropriate, adjuvant chemotherapy is given after the colorectal cancer is surgically removed. The surgery may not eliminate all of the cancer cells, some of which may remain in the lymph nodes or other organs. The adjuvant chemotherapy is used to kill any of these residual cancer cells.
Your doctor will talk with you about the best treatment strategy for your particular situation.
What chemotherapy agents are most commonly used to treat colorectal cancer?
5-Fluorouracil (5-FU), also known by its tradename Adrucil®, has been the first-line chemotherapy drug, along with the vitamin leucovorin, for advanced colorectal cancers for many years. 5-FU is usually given intravenously but is now available in an oral form as capecitabine (Xeloda®).
Two newer intravenous chemotherapy drugs--irinotecan (Camptosar®) and oxaliplatin — also are employed for the treatment of advanced colorectal cancers. Oxaliplatin is administered along with 5-FU and leucovorin for advanced colorectal cancers, while irinotecan is used alone or in combination with 5-FU/leucovorin for patients with metastatic colorectal cancer.
Are there any newer treatments for colorectal cancer?
Immunotherapy is a comparatively newer type of treatment in the fight against colorectal cancer. The goal of immunotherapy is to boost a patient’s immune reaction to the cancer cells, thus enabling them to fight the disease more effectively. There are two types of immunotherapy: active and passive.
Patients being given active immunotherapy are treated with products that stimulate their own immune system. Their own antibodies (immune system cells) are made to recognize an abnormal component in the cancer cells and then to selectively kill those cells. A vaccine is an example of an active immunotherapy. Active immunotherapy and vaccines against colorectal cancer are still under investigation.
Patients given passive immunotherapy are treated with products that have been manufactured in a laboratory to mimic the body’s antibodies (immune system cells). Unlike active immunotherapy agents, passive immunotherapeutic medications do not stimulate the patients’ own immune system to fight the disease. Rather, these man-made antibodies target specific components on the colorectal cancer cells in order to deliver cell-killing chemicals or radiation to the tumor, sparing the body’s healthy cells.
Monoclonal antibodies are a specific type of antibody, created in a lab to find and destroy a particular target – in this case, colorectal cancer cells. 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®) is an angiogenesis inhibitor, or anti-angiogenic agent. This monoclonal antibody prevents tumors from growing the blood vessels that allow them to receive the nutrients needed for their survival. More specifically, Avastin® stops the action of vascular endothelial growth factor (VEGF), a substance released by tumors to stimulate new blood vessel formation. Interfering with the blood supply to a tumor might slow its growth. Avastin® is given in combination with 5-FU-based chemotherapy to patients with metastatic colorectal cancer.
Cetuximab (Erbitux®), like Avastin®, is a monoclonal antibody, but it works by a different mechanism of action. This product slows cancer growth by targeting the epidermal growth factor receptor (EGFR), a protein found on the surface of about 60-80% of colon cancer cells. Erbitux® is believed to interfere with the growth of cancer cells by binding to the EGFR, preventing normal epidermal growth factors from binding to the cancer cells and from stimulating their growth. Erbitux® is used in patients who have metastatic colorectal cancer, alone or in combination with other chemotherapy agents, if other treatments have failed.
Panitumumab (Vectibix®) is yet another monoclonal antibody that, like Erbitux® , targets the EGFR. But in contrast to Erbitux® , since it is not manufactured from a mouse, Vectibix® may be less likely to cause an allergic reaction. It is used along with or following other chemotherapy agents for metastatic colorectal cancer that is not responsive to other treatments.