Chemotherapy destroys cells by stopping them from growing or multiplying. Healthy cells may also be harmed, especially cells that divide rapidly. Most side effects of chemotherapy are the result of harm caused to healthy cells. However, healthy cells usually regrow after chemotherapy treatment. The goals of chemotherapy are cure, control or palliation (control of symptoms) and comfort.
While surgery and radiation therapy destroy cancer cells in a specific area, chemotherapy works systematically (throughout the body) by destroying cancer cells that have metastasized (spread) from the primary (original) site. The body regulates the production of dividing cells by maintaining a balance between birth and death of cells. The body’s maintenance of this balance (homeostasis) is disturbed when cancer occurs, and cells grow out of control.
Today, there are more than 100 chemotherapy drugs used in various combinations. A single drug may be used for treatment, but more likely your treatment will consist of a combination of drugs. When using a combination of drugs, with different mechanisms of action, there is greater percentage of cancer cells destroyed. Combination therapy also reduces the chance of resistance to a particular drug and reduces toxicity to any one organ. Usually chemotherapy is given intravenously (I.V.), but it also may be administered orally or by injection or applied to the skin. In other circumstances drugs are delivered directly to the tumor or tumor site.
Chemotherapy is often given in cycles that include treatment alternating with rest periods. Rest periods give your body time to build healthy cells and for you to regain your strength. Keeping to your treatment schedule is important so you receive the most benefit. With each repeated cycle of chemotherapy, more of the cancer cells are killed, with the goal of eliminating enough of the tumor to allow your immune system to destroy any remaining cancer cells.
The following major drugs are used to treat colon and rectal cancer:
- 5-Fluouracil (5-FU) is administered intravenously in a timeframe that can either range from minutes to hours or as a continuous infusion over the course of several days. It works by binding to an enzyme important for making DNA and thus keeps cells from making DNA, which is vital to the growth of cancer cells. Common side effects may include nausea, vomiting, decreased blood count, increased risk of infection, mouth sores, diarrhea, skin color changes, poor appetite and hair thinning.
- Leucovorin is administered intravenously and is used with 5-Fluouracil (5-FU) to increase the effects of 5-FU. It has no anti-cancer activity by itself.
- Capecitabine (Xeloda) is an oral drug that is an analog of 5-Fluouracil. Common side effects may include nausea, vomiting, tiredness, mouth sores, skin dryness/irritation and tingling/itching/reddening of hands and feet. Less common side effects may include a sensation of pins and needles of the hands and feet due to nerve injury and abnormal liver function.
- Oxaliplatin (Eloxatin) is administered intravenously. It binds to DNA to stop the growth of cancer cells, which causes the cells to die. Common side effects may include nausea, vomiting, numbness and tingling of hands and/or feet or mouth due to nerve injury, abdominal pain, mouth sores, tiredness. Less common side effects may include difficulty walking, hair thinning, decreased blood count, increased risk of infection, poor tolerance to cold temperature and abnormal liver function.
- Irinotecan (Camptosar) is administered intravenously. It blocks the enzyme called topoisomerase I. Blocking this enzyme results in DNA breaks, which lead to cancer cell death. Common side effects may include nausea, vomiting, diarrhea, mouth sores, hair loss, decreased blood counts, loss of appetite and tiredness. Less common side effects may include cholinergic syndrome (which may include runny nose, increased saliva, sweating, tearing in the eyes, flushing, abdominal cramps, diarrhea), increased infection, abnormal liver function.
The following drugs are called targeted agents:
- Bevacizumab (Avastin) is administered intravenously. It is a type of targeted therapy that targets angiogenesis (harmful blood vessel formation by cancer cells). It blocks a protein called vascular endothelial growth factor (VEGF). By blocking VEGF, the drug stops the tumor from being able to create new blood vessels, thus limiting their supply of nutrients and slowing or stopping the growth. The drug may also work by making tumor blood vessels less leaky, allowing chemotherapy to get into cancer cells more effectively. Common side effects may include high blood pressure, headache, tiredness and loss of appetite. Less common side effects may include nosebleed, protein in the urine, nausea, vomiting and blood clots. Rare side effects may include stroke, heart attack, bowel perforation, slow healing of wounds, severe internal bleeding, confusion and severe allergic reaction.
- Cetuximab (Erbitux) is administered intravenously. It is a type of target therapy that targets the epidermal growth factor receptor (EGFR) pathway. By blocking EGFR protein, the drug interferes with cellular signaling that tells cancer cells to grow. Common side effects may include skin rash, tiredness and low blood magnesium level. Less common side effects may include infusion reaction (may include fever, headache, chills, itching, hives, nausea, shortness of breath) and diarrhea. Rare side effects may include severe allergic reaction and lung damage.
- Panitumumab (Vectibix) is administered intravenously. It also targets EGFR pathway similar to Cetuximab. Side effects are relatively similar to Cetuximab with the exception of less frequent infusion reactions.