Colorectal Cancer

What Is Colorectal Cancer?


Colorectal cancer, sometimes called colon cancer, is the third leading cause of cancer deaths among American men and women. It can start in the lining of your large intestine, also known as your colon. Tumors may also begin in the lining of the last part of your digestive tract, called your rectum.

Most colorectal cancers are "silent" tumors. They grow slowly, and you may not notice any symptoms until they’re large. But you can take some steps to prevent colorectal cancer, and you can cure it if you find it early. It’s important to have regular screening exams to spot cancer or pre-cancerous areas, especially if you have high odds of getting it.

Types of Colorectal Cancer

There are several types of colorectal cancer, based on where it starts.

  • Adenocarcinoma. This is the most common kind, making up 96% of cases. It starts in cells that make mucus for your colon and rectum.
  • Carcinoid tumor. This begins in cells that make hormones.
  • Gastrointestinal stromal tumor. This forms in cells in the wall of your colon that tell your gastrointestinal muscles to move food or liquid along.
  • Lymphoma. This is cancer of your immune system cells.
  • Sarcoma. This starts in connective tissues like blood vessels or muscle layers.

Colorectal Cancer Causes

Nearly all colon and rectal cancers begin as a polyp, a growth on the inner surface of your colon. Polyps themselves usually aren’t cancer.

The most common types of polyps in your colon and rectum include:

  • Hyperplastic and inflammatory polyps. These usually don’t carry a chance of cancer. But large hyperplastic polyps, especially on the right side of your colon, can be a problem. Your doctor will want to remove them.
  • Adenomas or adenomatous polyps. These are pre-cancerous. If you leave them alone, they could turn into colon cancer.

Colorectal cancer may also start in an area of abnormal cells, called dysplasia, in the lining of your colon or rectum.

Colorectal Cancer Risk Factors

Anyone can get colorectal cancer. It’s most common among African Americans and people over age 50. Things that can increase your chances of getting it include:

  • A personal or family history of colorectal cancer or polyps
  • Eating a lot of red and processed meats
  • Inflammatory bowel disease such as Crohn's disease or ulcerative colitis
  • Conditions passed down through your family, such as familial adenomatous polyposis and hereditary nonpolyposis colon cancer
  • Obesity
  • Smoking
  • Lack of activity
  • Heavy alcohol use
  • Type 2 diabetes
  • Breast cancer
  • Ovarian or uterine cancer diagnosed before age 50

Polyps might be more likely to contain cancer or carry a higher chance of cancer if:

  • They’re larger than 1 centimeter
  • You have more than two
  • They show signs of dysplasia


Colorectal Cancer Symptoms

You might not notice any signs of colorectal cancer. When you have symptoms, they can include:

  • A change in your bowel habits that doesn’t go away, such as constipation or diarrhea
  • A feeling that your bowel hasn’t emptied all the way after you poop
  • Bleeding from your rectum
  • Blood on or in your poop
  • Poop that’s narrower or thinner than usual
  • Belly discomfort
  • Stomach cramps
  • Weight loss with no clear cause
  • An unusually low number of red blood cells (anemia)
  • Weakness or fatigue
  • A lump in your belly or rectum

Colorectal Cancer Diagnosis

Your doctor may do one or more of these tests to spot polyps or colorectal cancer:

  • Rectal exam. Your doctor can feel for growths as part of a physical exam.
  • Colonoscopy. This is the standard screening test that experts recommend. Your doctor looks at your entire colon and rectum. They can also take out polyps and send them to a lab for testing.
  • Sigmoidoscopy. Your doctor looks at your rectum and the last part of your colon. They can also take a tissue sample for testing (called a biopsy).
  • Stool DNA. This test looks for certain gene changes that might be a sign of colon cancer.
  • CT colonography. This is a special X-ray (also called a virtual colonoscopy) of your entire colon. It takes less time and is less invasive than other tests. But if it shows a polyp, you’ll still need a colonoscopy.
  • Barium enema X-ray. This is a type of X-ray that involves putting dye in your colon. It can find trouble spots that might mean you need a colonoscopy.
  • Other imaging tests. MRI or ultrasound can give your doctor a better look at your organs.

Tumors may bleed in amounts so small that only special tests can find it. This is called occult bleeding, meaning you probably can’t see it with the naked eye. These tests can look for blood in your poop:

  • Fecal immunochemical test (FIT).  This reacts to part of human hemoglobin, a protein in red blood cells. You can do the test at home and mail a sample of poop to a lab.
  • Guaiac-based fecal occult blood tests (gFOBT). This uses a chemical to look for blood. You can do it at home and mail in a card with a sample of poop on it.

If either of these tests finds blood, your doctor will probably recommend a colonoscopy.


Colorectal Polyps

If a test finds a polyp, your doctor will take it out and send it to a laboratory. A specialist will look at it under a microscope. Your doctor will discuss the results with you. They will recommend next steps, including when to have another colonoscopy.

Colorectal Cancer Stages

If you have colorectal cancer, your doctor will do tests to find out whether it has grown or spread. This process is called staging. The stages of colorectal cancer are:

  • Stage 0. The cancer hasn’t gone past the inner layer of your colon or rectum. This is also called cancer in situ.
  • Stage I. The cancer has grown into the muscles of your colon or rectum.
  • Stage IIA. It’s spread through the colon or rectum wall.
  • Stage IIB. It’s grown into the lining of your abdomen (peritoneum).
  • Stage IIC. The cancer has spread through your colon or rectum wall and into nearby tissues.
  • Stage IIIA. It’s spread to three or fewer lymph nodes or to tissues around your colon or rectum.
  • Stage IIIB. It’s grown through the wall of your bowel or into nearby organs. It’s also spread to three or fewer lymph nodes or to tissues around your colon or rectum.
  • Stage IIIC. The cancer has spread to four or more lymph nodes.
  • Stage IVA. Cancer has spread to one part of your body that’s farther away, like your liver or lungs.
  • Stage IVB. It’s spread to more than one part of your body.
  • Stage IVC. Cancer has grown in the lining of your abdomen and possibly to lymph nodes or organs that are farther away.

Colorectal Cancer Treatment

Treatment will depend on several things, mainly the cancer’s stage and what parts of your body are involved. You might have one or more of these treatments:

  • Surgery. Your doctor can take out polyps and small tumors that haven’t spread during a colonoscopy or through a laparoscopy, in which they put special tools and cameras into your belly through small cuts. If the cancer has spread, you might have surgery to remove part of your colon (partial colectomy).
  • Radiation therapy. Strong X-rays or radioactive “seeds” can kill cancer cells.
  • Chemotherapy. Your doctor may also use medication to destroy cancer cells or keep them from growing.
  • Targeted therapy. This uses drugs that focus on specific things in cancer cells, like genes or proteins, to kill them or keep them from growing.
  • Immunotherapy. This is also called biologic therapy. Certain drugs can boost your immune system to help it fight cancer. 


Colorectal Cancer Prevention

A healthy lifestyle is the first step in preventing cancer of any kind. Don’t use tobacco, exercise regularly, and keep a healthy weight. Eat a diet low in red meat and high in fruits and vegetables.

Screening is crucial. The American Cancer Society recommends that people get regular screening exams from ages 45 to 75 if they have an average chance of getting colorectal cancer. This means that you don’t have symptoms and that neither you nor a close family member has had colorectal polyps, cancer, or inflammatory bowel disease.

The guidelines include at least one of these tests:

  • Tests for blood in your poop once a year
  • Stool DNA tests every 3 years
  • Flexible sigmoidoscopy every 5 years
  • CT colonography (virtual colonoscopy) every 5 years
  • Colonoscopy every 10 years

Talk to your doctor if you have one or more of the colorectal cancer risk factors. You might need to start screenings at a younger age, get tested more often, or have specific kinds of tests.

If you’re 76 through 85, talk to your doctor about whether you should be tested. The American Cancer Society doesn’t recommend testing for people older than 85.

Some studies have shown that aspirin and nonsteroidal anti-inflammatory drugs, or NSAIDs, may help prevent colorectal cancer. NSAIDs may also raise your odds of serious complications, such as stomach bleeding, heart attacks, and strokes. Some doctors recommend low-dose aspirin for adults ages 50 to 69. Talk with your doctor about whether it might help you.

WebMD Medical Reference Reviewed by Laura J. Martin, MD on March 01, 2020



Cleveland Clinic Department of Gastroenterology and Hepatology.


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National Institutes of Health.

U.S. Preventive Services Task Force.

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American College of Gastroenterology: “Colorectal Cancer.”

American Academy of Family Physicians: “Colorectal Cancer.”

Cancer Research UK: “Bowel cancer.”

National Cancer Institute: “Colorectal Cancer – Patient Version.”

Mayo Clinic: “Colon cancer.”

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