What is colon cancer?

Colon cancer, also known as colorectal cancer, develops when cells grow out of control in the colon or rectum, sections of the large intestine. The most common kind is adenocarcinoma of the colon, meaning it starts in the colon lining. Cancer may also arise elsewhere in the body and spread to the intestines, a process known as metastasis.

Who gets colon cancer?

Colorectal cancer is the third most common cancer in the United States and the second leading cause of cancer-related death. There are about 95,500 new cases and close to 50,200 deaths annually, according to the American Cancer Society. New colon cancer cases and deaths among older adults have been decreasing in recent years, likely due to more screening, however the rates are increasing among people younger than 50.

Colon cancer affects women and men equally in the United States. African Americans have higher rates of colon cancer occurrence and death. Black men and women are about 25 percent more likely to develop colon cancer than whites. Latinos or Hispanics have the lowest rates of colon cancer occurrence and death.

What are the risk factors for colon cancer?

Being older than 50 is the biggest risk factor for developing colon cancer. This is because colon and rectal tumors can take a long time to form. Sometimes benign (noncancerous) tumors in the colon can take 10 to 20 years to progress to cancer.

Other risk factors include genetic factors, a family history of colon cancer or polyps in the colon or rectum, and long-term inflammatory bowel disease (such as Crohn’s disease or ulcerative colitis). Lifestyle factors are known to increase the risk of colon cancer, including being obesity, lack of physical activity, tobacco use, alcohol consumption and a diet high in fat and red meat. A diet high in fruits and vegetables may protect against colon cancer.

What are the symptoms of colon cancer?

After food is mostly digested by other parts of the stomach and small intestines, the colon absorbs water and salt from and stores what’s left as waste in the rectum before it is excreted as feces.

Colon cancer can cause many symptoms, which include: 

  • Changes in bowel habits such as diarrhea or constipation
  • Blood in the stool
  • Feeling the need to have a bowel movement even after doing so
  • Persistent abdominal pain or cramps
  • Unexplained weight loss
  • Iron deficiency (anemia)

 Many people with colon cancer do not develop symptoms until its late stages, when it is harder to treat. This is why screening is important for prevention.

How is colon cancer diagnosed?

Early detection and treatment of colon cancer increases the likelihood of long-term survival. Doctors primarily use two types of tests to screen for colon and rectal cancer. Colonoscopy uses a flexible lighted tube to view the entire colon, while sigmoidoscopy views only the lower part of the colon and rectum. Another type of test looks for blood or DNA changes in a stool sample.

Because of widespread screening, colon cancer is often detected before symptoms occur. Often polyps (abnormal precancerous growths) and some small tumors can be removed during a colonoscopy. Other imaging such as X-rays or computed tomography (CT) scans may be done to see if cancer has spread.

How is colon cancer treated?

Treatment for colon cancer depends on how advanced the cancer is when it is detected, where it is located, how many tumors there are, how large they are and whether they have spread to nearby lymph nodes and other parts of the body.

Surgery: Some small and localized tumors in the colon and rectum, or precancerous growths that could become cancerous, can be surgically removed.

Radiation: Radiation may be used to shrink tumors, which can help relieve pain and other symptoms. It is often used in conjunction with other forms of treatment.

Chemotherapy: Traditional chemotherapy works by killing fast-growing cells, including cancer cells. It can also destroy rapidly dividing healthy cells, such as those in the gut or hair follicles, leading to side effects including nausea and hair loss.

Targeted therapy: Targeted drugs work against cancers with specific characteristics. For example, they may interfere with signaling pathways that regulate cell growth. Targeted treatment is often better tolerated than chemotherapy, but cancer may develop resistance over time.

Immunotherapy: The newest type of treatment helps the immune system fight cancer. For example, some tumors can turn off immune responses against them, and drugs known as checkpoint inhibitors can restore T cells’ ability to recognize and destroy cancer cells. Current immunotherapy drugs work for only a subset of patients, and it is hard to predict who will benefit.

For more information on colon and rectal cancer, see the following resources:

American Cancer Society

National Cancer Institute

Last Revised: October 20, 2017