Colon and Rectal Cancers

Colon cancer is a cancer that forms in the tissues of the colon (the longest part of the large intestine). Rectal cancer is a cancer that forms in the tissues of the rectum (the last several inches of the large intestine closes to the anus. Colorectal cancer affects the digestive system. This includes the large and small intestines. The large intestine is also called the colon.

Colorectal cancer is the third leading cause of cancer-related deaths in the United States among both men and women. For men, only lung and prostate cancers show higher numbers. In women, only lung and breast cancers outrank colorectal cancer.

The intestines break down and absorb food and water. They also carry away the body's digestive waste products. Genetic screening can help determine if patients may be at risk for getting the disease.


Adenocarcinoma of the colon and rectum grows slowly. A long time may pass before it becomes large enough to cause symptoms.

Routine exams are important for early diagnosis.

When symptoms do occur, they vary depending on the location of the tumor, its type, how far it has spread and complications it may have caused.

On the right-hand side of the colon, blockage usually doesn't occur until later stages. This is because the space inside the colon is large, the colon wall is fairly thin and the material passing through is mostly liquid. Some tumors may grow big enough to be felt from the outside of the body. If there is bleeding inside, it usually isn't obvious. However, a person may feel weak or tired because of severe anemia caused by loss of blood.

On the left-hand side of the colon, the space inside the colon is smaller and the material that passes through it is semi-solid. Colon cancer can cause both constipation and diarrhea. A person may feel cramp-like pain in the stomach. The stool may be streaked or mixed with blood.

In rectal cancer, the most common symptom is usually bleeding when going to the bathroom.

Cancer of the rectum should be considered whenever there is rectal bleeding, even if other causes such as hemorrhoids are present. A person may feel as if there is incomplete evacuation. There usually is no pain until later stages of the condition.

Symptoms of advanced disease include:

  • A feeling of being full very quickly while eating
  • Weakness and pain in the abdominal area


Causes and Risk Factors

There is no single cause of intestinal cancer. Several risk factors may play a role in its development.

Persons between the ages of 40 and 75 are at greater risk of getting colorectal cancer than younger people. More women get colon cancer. More men get rectal cancer.

Conditions such as familial polyposis, Lynch syndrome, Crohn's disease or ulcerative colitis (ulcers in the lining of the large intestines) tend to increase the risk for the disease. Brothers, sisters and children of those already diagnosed with colorectal cancer have a greater chance of getting the disease later in life.

Population groups who have a high rate of colorectal cancer tend to eat low-fiber diets high in animal protein, fat and refined carbohydrates. The exact way the condition occurs is not yet known.


Screening is very effective for detecting early stages of colorectal cancer. Starting at age 40, even people who have no risk factors and no symptoms should have a digital rectal exam and a test for blood in the stool every year. At age 50, everyone should have a sigmoidoscopy or a similar test.

Screening tests include:

  • Digital rectal exam - The doctor inserts a gloved finger into the rectum to feel for lumps and to check for blood in the stool.
  • Sigmoidoscopy - An instrument called a sigmoidoscope is inserted to look inside the rectum and part of the colon.
  • Colonoscopy - An instrument called colonoscope is used to examine the rectum and the entire colon.
  • Computed tomography scan - A special X-ray creates a computerized picture of the colon and rectum.
  • Barium enema - A liquid is inserted into the rectum, and a series of X-rays are taken. This allows doctors to look for abnormal growths in the colon and rectum.
  • Biopsy - If test results are abnormal, the doctor may examine a small piece of the tumor under the microscope.
  • Genetic risk assessment - This is a method of identifying genes that may increase the chance of getting certain diseases.


The main treatment for colon cancer is surgery. The part of the large bowel with cancer is removed, along with surrounding lymph nodes. The remaining bowel is joined together. Surgery is a cure for 70% of patients with colon cancer. Persons who have cancer that is limited to the mucous lining of the colon have the best chance of survival. Persons who have cancer in the lymph nodes have a less optimistic outlook.

Treatment of rectal cancer depends on how far the tumor has spread and how close it is to the rectum.

If there is not enough healthy colon to reconnect after the tumor is removed, the person may need a colostomy. This is rarely permanent. For this procedure, a surgical opening is made in the abdomen and the end of the bowel is placed through the hole. A bag is placed over the opening to collect the stool.

A combination of radiation therapy and chemotherapy may be helpful for rectal cancer patients, especially if one to four lymph nodes are affected. Careful planning and attention is given to avoid injury to the small intestine.

Follow-up care with the surgeon, gastroenterologist and oncologist is important. The most common time a cancer recurs is within the first two years following diagnosis and treatment. Periodic checkups may include a physical exam, blood tests, colonoscopy, CT scan or PET scan.

The frequency of follow-up after surgery varies. Most experts recommend two annual inspections of the remaining bowel with colonoscopy or X-rays. If results are negative, repeat evaluations may be done at two- to three-year intervals.

When it is not possible to remove the cancer entirely, surgery may be helpful in managing symptoms. Chemotherapy can be used for advanced colon cancer to slow progression of the disease.