After surgery, radiation can kill leftover deposits of cancer not be seen during the surgery. Radiation can also ease symptoms of advanced cancer, such as intestinal blockage, bleeding, or pain. The side effects of radiation therapy include mild skin irritation, nausea, diarrhea, or fatigue. Physicians use chemotherapy to treat cancer that has spread beyond the rectum or to relieve the symptoms of advanced cancer. Sometimes, 5-FU is more effective when given with other drugs, such as leucovorin or levamisole.
Chemotherapy drugs kill cancer cells, as well as normal ones.
Careful attention must be paid to avoiding or minimizing side effects, which can include nausea and vomiting, appetite loss, hair loss, and mouth sores. Because chemotherapy can damage the blood-producing cells of the bone marrow, patients may have low blood cell counts. This can result in an increased chance of infection, bleeding or bruising after minor cuts or injuries, and fatigue. If cancer is found, physicians then determine how far it has spread. This process is called staging.