Types of Cancer in the Lower Gastrointestinal Tract

Anal Cancer

The anal canal connects the anus (the opening at the lowest end of the intestines) with the rectum (the last part of the large intestine). Most cancers of the anal canal can be cured using radiation therapy and chemotherapy alone. This approach is preferred because surgical removal generally requires a permanent colostomy bag, a pouch worn on the outside of the body to collect stool from the colon when part of the colon has been surgically removed. Radiotherapy and chemotherapy are given at the same time, to kill cancer cells more effectively. This means that after treatment you are likely to retain control of your bowel movements through the anus.

Radiation therapy is typically given over a period of five to six weeks. A small dose is given each day to the anal canal and other areas around the pelvis and groin to kill cancer cells that may have traveled to nearby lymph nodes.

Rectal Cancer

Cancers of the rectum are typically treated with a combination of chemotherapy, radiation and/or surgery depending on the location and extent of disease; however, very small tumors can sometimes be treated with surgery or immunotherapy alone. For more advanced tumors, this combination of treatment offers the highest likelihood of destroying cancer cells. Radiation therapy is usually delivered prior to surgery, although occasionally it will follow surgery. Chemotherapy may be used in conjunction with radiation therapy. This combination makes the cancer cells more sensitive to radiation therapy and more likely to respond to the treatment. New studies in rectal cancer treatments are looking at whether certain patients can skip radiation therapy to the pelvis (and still go to surgery), or not require surgery after being given chemotherapy and radiation together.

The benefits of radiation therapy for rectal cancer are:

• It lowers the risk of cancer returning in the pelvic area.
• It makes the tumor smaller and easier to remove completely during surgery or may allow some patients to avoid surgery.
• It may eliminate the need for a permanent colostomy after surgery.

Radiation therapy is typically given over a period of five to six weeks. A small dose is given each day to the rectum and other areas in the pelvis to kill cancer cells that may have spread to nearby lymph nodes. In some instances, the radiation may be given over the course of one week with higher daily doses.

Colon Cancer

Cancers of the colon are typically treated with chemotherapy, targeted therapy (such as bevacizumab), and surgery (that does not involve a permanent colostomy bag, but you may be given a temporary one). Some earlier stage colon cancers can be treated with surgery alone. Radiation therapy is not usually involved in most stage I, II or III colon cancers. For some stage IV cancers (cancers that have spread to other places of the body at diagnosis), a lower dose of radiotherapy is sometimes used to help reduce pain and bowel obstruction caused by the cancer (for comfort and to relieve suffering).

Cancer That Has Spread

Sometimes colorectal and anal cancers can spread, or metastasize to, other areas of the body. In these instances, delivering radiation therapy to these areas can shrink or destroy these tumors to improve outcomes or alleviate symptoms as palliation (for comfort and to relieve suffering).

For each treatment, you will be placed on the treatment table by radiation therapists who are operating the radiation machine, known as a linear accelerator or linac. They will ensure that you are correctly aligned by performing scans while you are on the treatment table. Once you are in the correct position, the beam is switched on.

You will not feel anything while radiation is going into the tumor. Radiation is confined to the pelvis. Parts of the linear accelerator will move around you but will not touch you. You will not be radioactive after your treatments, and you may come in contact with friends and family.

Cancer That Has Returned

If cancer has returned in the same area that was previously treated, radiation therapy to the pelvis for a second time may be necessary. This repeat course may be necessary to destroy the new tumor, to shrink it so that it can be removed or to stop it from growing further. Talk to your doctors about whether this approach is the best for you since treating an area that has already been treated with radiation therapy can be challenging. In some cases, intraoperative radiotherapy (IORT) can be used as part of the treatments for cancer cases that have returned.