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What is colorectal cancer?

Colorectal cancer is cancer that starts in the colon or the rectum. These cancers can also be named colon cancer or rectal cancer, depending specifically on where they start. They are often grouped together because they have many features in common.

How does colorectal cancer start?

Most colorectal cancers begin as a growth on the inner lining of the colon or rectum called a polyp. Some types of polyps can change into cancer over the course of several years, but not all polyps become cancer. The chance of changing into cancer depends on the kind of polyp.

The 2 main types of polyps are:

  • Adenomatous polyps (adenomas): These polyps sometimes change into cancer. Because of this, adenomas are called a pre-cancerous condition.
  • Hyperplastic polyps and inflammatory polyps: These polyps are more common, but in general they are not pre-cancerous.

Dysplasia, another pre-cancerous condition, is an area in a polyp or in the lining of the colon or rectum where the cells look abnormal (but not like true cancer cells).

If cancer forms in a polyp, it can eventually begin to grow into the wall of the colon or rectum.

The wall of the colon and rectum is made up of several layers. Colorectal cancer starts in the innermost layer (the mucosa) and can grow through some or all of the other layers. When cancer cells are in the wall, they can then grow into blood vessels or lymph vessels (tiny channels that carry away waste and fluid). From there, they can travel to nearby lymph nodes or to distant parts of the body.

The stage (extent of spread) of colorectal cancer depends on how deeply it grows into the wall and if it has spread outside the colon or rectum.

Types of cancer in the colon and rectum

Adenocarcinomas make up more than 95% of colorectal cancers. These cancers start in cells that form glands that make mucus which lubricates the inside of the colon and rectum. When doctors talk about colorectal cancer, they are almost always talking about this type.

Other, less common types of tumors can also start in the colon and rectum. These includes:

  • Carcinoid tumors
  • Gastrointestinal stromal tumors (GISTs)
  • Lymphomas
  • Sarcomas

Colorectal cancer risks factors

Researchers have found several risk factors that might increase a person’s chance of developing colorectal polyps or colorectal cancer.

  • Being overweight or obese
  • Physical inactivity
  • Diets high in red and processed meats
  • Cooking meats at very high temperatures (frying, broiling, or grilling) create chemicals that might raise your cancer risk, but it’s not clear how much this might increase your colorectal cancer risk.
  • Diets high in vegetables, fruits, and whole grains have been linked with a lower risk of colorectal cancer, but fiber supplements have not been shown to help.
  • Smoking
  • Heavy alcohol use
  • Age 50+
  • A personal history of colorectal polyps or colorectal cancer
  • A personal history of inflammatory bowel disease (IBD)
  • A family history of colorectal cancer or adenomatous polyps
  • Having an inherited gene mutations
  • Your racial and ethnic background (Higher in African Americans and Jews of Eastern European descent)
  • Having type 2 diabetes

Can colorectal polyps and cancer be found early?

In many people, screening can also prevent colorectal cancer by finding and removing polyps before they have the chance to turn into cancer.

Tests used to screen for colorectal cancer include:

  • Guaiac-based fecal occult blood test (gFOBT) and fecal immunochemical test (FIT): Samples of stool (feces) are checked for blood, which might be a sign of a polyp or cancer.
  • Stool DNA test: A sample of stool is checked for certain abnormal sections of DNA (genetic material) from cancer or polyp cells.
  • Sigmoidoscopy: A flexible, lighted tube is put into the rectum and lower colon to check for polyps and cancer.
  • Colonoscopy: A longer, flexible tube is used to look at the entire colon and rectum.
  • Double-contrast barium enema: This is an x-ray test of the colon and rectum.
  • CT colonography (virtual colonoscopy): This is a type of CT scan of the colon and rectum.
  • gFOBT, FIT, and stool DNA testing mainly find cancer, but can find some polyps.

Sigmoidoscopy, colonoscopy, double-contrast barium enema, and CT colonography are good at finding both cancer and polyps. These tests are preferred if they are available and you are willing to have them.

For most adults, the American Cancer Society recommends starting screening with one of these tests at age 50. Some people at higher risk for colorectal cancer might need to start screening earlier.

Colorectal cancer treatment

If you’ve been diagnosed with colorectal cancer, your cancer care team will discuss your treatment options with you. It’s important that you think carefully about each of your choices. You will want to weigh the benefits of each treatment option against the possible risks and side effects.

Which treatments are used for colorectal cancer?

There are several ways to treat colorectal cancer, depending on its type and stage.

  • Surgery (the type of surgery will depend on whether it is for colon or rectal cancer)
  • Radiation therapy
  • Chemotherapy
  • Targeted therapy
  • For advanced colon and rectal cancer, ablation or embolization may also be used.

Depending on the stage of cancer and other factors, different types of treatment may be combined at the same time or used after one another.

Which doctors treat colorectal cancer?

Based on your treatment options, you might have different types of doctors on your treatment team. These doctors could include:

  • A gastroenterologist: a doctor who treats disorders of the gastrointestinal (digestive) tract
  • A surgical oncologist (oncologic surgeon): a doctor who uses surgery to treat cancer
  • A colorectal surgeon: a doctor who uses surgery to treat diseases of the colon and rectum
  • A radiation oncologist: a doctor who treats cancer with radiation therapy
  • A medical oncologist: a doctor who treats cancer with medicines such as chemotherapy or targeted therapy

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Some of the content contained in this section has been adapted from the following sources:
“What is colorectal cancer.” Learn About Cancer. American Cancer Society, Inc. 15 Oct. 2015. Web. 6 June 2016.
“Colon Cancer.” Cancer Facts and Information. The University of Texas MD Anderson Cancer Center. 2016. Web. 6 June 2016.
“Colon Cancer.” Diseases and Conditions – Colon Cancer. Mayo Foundation for Medical Education and Research. 2016. Web. 6 June 2016.