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Facts About Colon, Rectal and Anal Cancers

It is estimated that 135,430 Americans will be diagnosed with colon cancer this year. Colorectal cancer is the third most commonly diagnosed cancer in men and women. Of those, 39,910 will be diagnosed with rectal cancer. Patients with these types of cancer often benefit from radiation therapy as part of treatment. Some cancers involving the bowel happen within families (hereditary colorectal cancers). It is important to discuss your diagnosis with family members so they can decide with their doctors whether they need to be screened for colorectal cancers. This is especially important if you were diagnosed with a colorectal cancer at a young age or if there are several other types of cancers that run in your family.


Radiation Therapy

Radiation therapy is often used in conjunction with surgery and chemotherapy to treat cancers of the colon, rectum and anus. Treatment involves focused radiation to the bowel and pelvis to treat cancer cells in the area.

Surrounding healthy tissue can be affected, but normal cells are often better able to heal from radiation injury, compared to cancer cells, because normal cells have maintained the ability to repair radiation-induced damage.

  • For colon cancer, depending on the location and stage of your cancer, radiation can lower the chance of recurrence.
  • For some rectal cancers, radiation therapy is given with chemotherapy to make the tumor smaller so it can be removed more easily during surgery. In some cases, radiation can allow an organ-sparing surgery to be possible. It is also common for radiation and chemotherapy to be given before surgery for rectal cancer.
  • Anal cancer can often be treated with radiation therapy and chemotherapy, as an organ-preserving approach that avoids the need for surgery.

Surgery often plays a key role in treatment. For colorectal cancers, it is the main curative treatment. The surgeon will determine how much of the large bowel needs to be removed, but often it involves removal of a section of the colon. Because the tumor can spread to lymph nodes nearby, often some lymph nodes are removed at the time of surgery. Depending upon the location of the tumor, surgery may or may not allow normal bowel function afterwards.

For anal cancers, surgery is less frequently used at the time of diagnosis because effective organ-preserving approaches are available. If bowel function is poor, sometimes surgery is used at first, but often it is reserved as a second chance for cure where organ-preserving treatment does not succeed. Because surgery for the anal canal involves removing the area responsible for how you go to the bathroom, a surgery called a colostomy to re-route bowel movements is usually necessary as well.

Medical Therapy
While surgery and radiation focus directly on treating the bowel or pelvic area, medication is often recommended to improve cure rates. A medical oncologist will evaluate you and determine what medications may be most helpful.


External beam radiation therapy involves a series of daily outpatient treatments that accurately deliver radiation to the area needing therapy. The radiation beam usually comes from a machine called a linear accelerator or linac.

Before beginning treatment, you will be scheduled for a simulation to map out the area to be treated. This will involve having X-rays and/or a CT scan. Landmarks placed on your skin (often tiny tattoos) allow the radiation therapists delivering your treatments to precisely position you each day.

To minimize side effects, the treatments are usually given over about five or six weeks, five days a week (Monday through Friday). This allows your doctors to get enough radiation into your body to kill the tumor cells while giving healthy cells time to recover each day.

Technical terms that may be mentioned for colorectal and anal cancer treatments include 3-dimensional conformal radiation therapy (3-D CRT) and intensity modulated radiation therapy (IMRT). Your radiation oncologist can provide more information about these different techniques.


It is important to care for yourself as well as possible during radiation therapy.

  • A balanced diet, a mild amount of physical activity, and taking time to rest are all important parts of your cancer treatment.
  • Nutrition is important. Eat a balanced diet. Let your doctor know if you have trouble swallowing, food tastes funny or you have trouble eating.
  • Follow your doctor’s orders, and if you are unsure of anything, ask your nurse or doctor any question you may have about your treatment.
  • Be sure to tell your radiation oncologist about any vitamins or dietary supplements that you are currently taking to make sure they are safe to take during radiation therapy.
  • Treat the skin exposed to radiation with special care. Stay out of the sun, avoid hot or cold packs, and only use lotions and ointments after checking with your nurse or doctor.
  • You should also be sure to clean the skin over the areas receiving radiation therapy with warm water and mild soap.

Completing treatment and recovery can be challenging. Seek out help from support groups and friends ahead of time. If you have a support network in place before and during treatment, it will be easier to get through side effects since people you can count on will be around to help you. If you need additional support, let your doctor and nurse know.


  • Radiation therapy to the abdomen and pelvis may cause more frequent bowel movements, occasionally with diarrhea, abdominal cramping or rectal discomfort. It may also cause more frequent urination, sometimes with a burning feeling or cause a small amount of blood to appear in the urine or stool. These should resolve after treatment ends.
  • Some patients may also feel tired or lose their appetite. This is temporary as well.
  • Possible skin irritation problems depend on your tumor and the areas needing treatment. For anal cancer patients, a pronounced but temporary skin irritation is usually the major side effect from the treatment. Talk with your doctor and treatment team about any new symptoms you experience during treatment.
  • Side effects that occur are not the same for all patients. Ask your doctor what you might expect from your specific treatment program.
  • It is likely you will receive chemotherapy in addition to radiation therapy. The side effects from the chemotherapy will depend on the drugs being prescribed and how often you are to receive them. Ask your medical oncologist about chemotherapy side effects you may experience. Side effects often can be controlled with medications or changes in your diet. Tell your nurse or doctor if you experience any of them, so they can work to help you feel better.

© American Society for Radiation Oncology, 2019.