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Gastrointestinal Complications



In cancer patients, the most common cause of diarrhea is cancer treatment (chemotherapy, radiation therapy, bone marrow transplantation, or surgery). Other causes of diarrhea include antibiotic therapy, stress and anxiety related to being diagnosed with cancer and undergoing cancer treatment; and infection. Infection may be caused by viruses, bacteria, fungi, or other harmful microorganisms. Antibiotic therapy can cause inflammation of the lining of the bowel, resulting in diarrhea that often does not respond to treatment. Other causes of diarrhea in cancer patients include:

Undergoing surgery to the stomach and/or intestines can affect normal bowel function and cause diarrhea. Some chemotherapy drugs cause diarrhea by affecting how nutrients are broken down and absorbed in the small bowel. Radiation therapy to the abdomen and pelvis can cause inflammation of the bowel. Patients may have problems digesting food, and experience gas, bloating, cramping, and diarrhea. These symptoms may last up to 8 to 12 weeks after therapy or may not develop for months or years. Treatment may include diet changes, medications, or surgery. Patients who are undergoing radiation therapy while receiving chemotherapy often experience severe diarrhea. Hospitalization may not be required, since an outpatient clinic or special home care nursing may give the care and support needed. Each patient's symptoms should be evaluated to determine if intravenous fluids or special medication should be prescribed.

Patients who undergo donor bone marrow transplantation may develop graft-versus-host disease (GVHD). Stomach and intestinal symptoms of GVHD include nausea and vomiting, severe abdominal pain and cramping, and watery, green diarrhea. Symptoms may occur 1 week to 3 months after transplantation. Some patients may require long-term treatment and diet management.


Because diarrhea can be life-threatening, it is important to identify the cause so treatment can begin as soon as possible. The doctor may ask the following questions:

The doctor will also do a physical examination that should include checking blood pressure, pulse, and respirations; evaluation of the skin and tissue lining the inside of the mouth to check for blood circulation and amount of fluid in the tissue; examination of the abdomen for pain, tenderness, and bowel sounds; and a rectal exam to check for stool impaction and collect stool to test for blood.

Stool may be tested in the laboratory to check for bacterial, fungal, or viral infections. Blood and urine tests may be done to detect fluid and blood chemistry imbalances or infection.

In some cases, abdominal x-rays may also be done to identify bowel obstruction or other abnormalities. In rare cases, a thorough examination of the rectum and colon may be done with a lighted tube inserted through the anus and into the colon.


Diarrhea is treated by identifying and treating the problems causing diarrhea. For example, diarrhea may be caused by stool impaction and medications to prevent constipation. The doctor may make changes in medications, diet, and fluids. Diet changes that may help decrease diarrhea include eating small frequent meals and avoiding some of the following foods:

For mild diarrhea, a diet of bananas, rice, apples, and toast (the BRAT diet) may decrease the frequency of stools. Patients should be encouraged to drink up to 3 quarts of clear fluids per day including water, sports drinks, broth, weak decaffeinated tea, caffeine-free soft drinks, clear juices, and gelatin. For severe diarrhea, the patient may need intravenous fluids or other forms of intravenous nutrition. (See the Diarrhea section in the PDQ summary on Nutrition in Cancer Care for more information.)

To manage diarrhea caused by graft-versus-host disease (GVHD), the doctor may recommend a special 5-phase diet. During phase 1, the patient receives intravenous fluids and nothing by mouth to rest the bowel until the diarrhea slows down. In phase 2, the patient may begin drinking fluids. If the patient is able to drink fluids and the diarrhea improves, he or she may begin phase 3, eating solid foods that are low-fiber, low-fat, low-acid, and do not irritate the stomach. In phase 4, the patient is gradually allowed to eat regular foods. If the patient is able to eat regular foods without any episodes of diarrhea, he or she may begin phase 5, eating their regular diet. Many patients may continue to have problems digesting milk and dairy products.

Depending on the cause of the diarrhea, the doctor may change the laxative therapy regimen or may prescribe medications that slow down bowel activity, decrease bowel fluid secretions, and allow nutrients to be absorbed by the bowel.


Probiotics are live microorganisms taken as nutritional supplements or added to foods to improve digestion and bowel function. There are many types of probiotics, such as Lactobacillus. Probiotics help support the normal balance of bacteria in the colon. They may be used to:

In a clinical trial of patients with cancer who received radiation therapy to the pelvis, those who took a probiotic product had less severe and less frequent diarrhea with no side effects, compared to those who took a placebo. Probiotics are being studied in patients with familial adenomatous polyposis and in adults, children, and adolescents who are undergoing stem cell transplantation.

Current Clinical Trials

Check NCI’s list of cancer clinical trials for U.S. supportive and palliative care trials about diarrhea that are now accepting participants. The list of trials can be further narrowed by location, drug, intervention, and other criteria.

General information about clinical trials is also available from the NCI Web site.