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Colorectal cancer

Medically reviewed by Last updated on Jul 28, 2023.

What is colorectal cancer?

Harvard Health Publishing

Colorectal cancer is an uncontrolled growth of abnormal cells in the colon and/or rectum.

Together, the colon and rectum make up the large intestine. The large intestine carries waste from the small intestine and eliminates it through the anus.

Colorectal tumors often begin as small growths (polyps) on the inside of the large intestine. Polyps that are not removed eventually can become cancerous.

Risk Factors of colorectal cancer

The major risk factors for colorectal cancer include:

  • personal history of colorectal cancer
  • personal history of colon polyps
  • certain inherited genes linked to colon polyps and cancer
  • inflammatory bowel disease, including persistent ulcerative colitis and Crohn's disease
  • family history of colorectal cancer.

Additional potential risk factors:

  • cigarette smoking
  • sedentary lifestyle
  • low intake of fruits and vegetables
  • high consumption of processed meats
  • low vitamin D levels.

Symptoms of colorectal cancer

Polyps and early colorectal cancer generally don't cause symptoms. As a result, they are usually caught during screening.

More advanced cancer can cause:

  • more or less frequent bowel movements than usual
  • diarrhea or constipation
  • blood in the stool (bright red, black or very dark)
  • narrowed stools (about the thickness of a pencil)
  • bloating, fullness or stomach cramps
  • frequent gas pains
  • a feeling that the bowel does not empty completely
  • weight loss without dieting
  • continuing fatigue.

Diagnosing colorectal cancer

If your doctor suspects colorectal cancer, he or she will perform a colonoscopy. This is done with an instrument called a scope. A scope is a flexible tube with a camera attached at one end. The doctor inserts the scope into your rectum and colon to look for polyps or cancer.

During the procedure, one or more biopsies may be performed. The sample(s) are sent to the laboratory for examination under the microscope.

Your doctor may also order additional tests, such as blood tests and computed tomography (CT) scans.

Expected duration of colorectal cancer

Without treatment, colon cancer will continue to grow.

Preventing colorectal cancer

The best defense against colorectal cancer is regular screening. Screening tests are designed to find polyps so they can be removed before they become cancerous.

The United States Preventive Services Task Force (USPSTF) and the American Cancer Society recommend that all adults at average risk for colorectal cancer begin screening at age 45 because of a rising number of younger people diagnosed with the disease. People at higher risk should begin screening earlier. You are at high risk if you:

  • have been diagnosed with polyps before age 50
  • have inflammatory bowel disease, including ulcerative colitis and Crohn's disease
  • have a genetic disorder that increases your likelihood of developing colorectal cancer
  • have one or more first degree relatives (a parent or sibling) diagnosed with colon cancer before age 50.

Recommended screening methods include:

  • Digital rectal examination. Your doctor inserts a gloved finger into your anus to check for abnormal lumps or masses. This should not be used as the only screening method.
  • Fecal occult blood test. This test detects small amounts of blood in the stool. However, blood in the stool does not necessarily mean you have colon cancer.
  • Stool test for DNA (Cologuard). This test detects abnormal genetic markers in the stool and also detects small amounts of blood.
  • Sigmoidoscopy. The doctor uses a scope to examine the rectum and part of the colon.
  • Colonoscopy. The doctor uses a scope to examine your entire colon and rectum.
  • Virtual colonoscopy. Images of the colon are taken with computed tomography (CT) scans.

Daily exercise and a diet rich in fruits and vegetables may lower your risk of colorectal cancer.

Taking aspirin or folate every day may also reduce your risk. Talk to your doctor to see if this is appropriate for you.

Treatment options

The following list of medications are in some way related to or used in the treatment of this condition.

View more treatment options

Treating colorectal cancer

Surgery is the main treatment for colorectal cancer. You may also have chemotherapy or radiation.

The extent of surgery and whether you need treatment after surgery depends on:

  • whether the cancer is in the colon or rectum
  • the stage of the disease. The cancer's stage depends on how far the cancer has spread.

Following are the stages of colorectal cancer, along with recommendations for treatment in addition to surgery:

  • Stage 0. Cancer remains within the inner layer of the colon or the rectal lining. Your doctor is unlikely to recommend any treatment, except for additional, regular follow up, after surgery to remove polyps or cancer.
  • Stage I. Cancer has grown through the inner rectal wall or the inner lining of the colon and the underlying layers. It has not broken through the colon wall. Usually, no treatment is recommended after surgery.
  • Stage II. Cancer has grown through the colon or rectal wall. It has not spread to nearby lymph nodes. The doctor may recommend chemotherapy after surgery in some cases of colon cancer. For rectal cancer, chemotherapy and radiation can be used before or after surgery.
  • Stage III. Cancer has spread to nearby lymph nodes but not to other parts of the body. For colon cancer, chemotherapy typically is recommended after surgery. For rectal cancer, chemotherapy and radiation usually are given before or after surgery.
  • Stage IV. Cancer has spread to distant organs. Treatment after surgery consists of chemotherapy, radiation therapy or both to relieve the symptoms of advanced cancer and, in rectal cancer, to prevent the blockage of the rectum. Occasionally, surgery is needed to remove cancer from the sites where it has spread.

Colon cancer

Surgery for colon cancer removes the cancerous area of the colon, some surrounding normal tissue and nearby lymph nodes.

Recovery time depends on several factors, including the person's age, general health and the extent of the surgery.

Rectal cancer

Treatment for rectal cancer often combines surgery with chemotherapy and radiation, which can be given before or after surgery.

Early stage rectal cancer may only require removal of polyps. Late stage rectal cancer may require removal of the rectum, anus, and part of the colon.

In some cases of late-stage surgery, the surgeon must reroute the colon through a hole in the abdomen to create a new way for the body to eliminate waste. This is called a colostomy.

When to call a doctor

Visit a doctor for regular colorectal cancer screening. Also, see your doctor if you have any signs or symptoms of colorectal cancer.


The outlook for colorectal cancer depends on the stage of the disease. Nearly everyone with stage 0 cancer will survive 5 years or more. The outlook is less favorable for people with stage IV cancer.

Additional info

American Cancer Society (ACS)

Cancer Research Institute

Centers for Disease Control and Prevention (CDC)

National Cancer Institute (NCI)

Learn more about Colorectal cancer

Treatment options

Care guides guides (external)

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.