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What Is Colon and Rectal Cancer (Colorectal Cancer)?

Outline of adult abdomen showing arteries and lymph nodes of colon.Cancer happens when cells in the body begin changing and multiplying out of control. These cells can form lumps of tissue called tumors. Cancer that forms in the colon is called colon cancer. Cancer that forms in the rectum is called rectal cancer. These cancers are similar, so they are sometimes just called colorectal cancer.

Understanding the colon and rectum

The colon and rectum make up the large intestine (or large bowel), which is last part of the digestive tract. The colon is a muscular tube that forms the last part of the digestive tract. It absorbs water and stores food waste. The colon is about 5 feet long. The rectum is the last 6 inches of the large intestine. The colon and rectum have a smooth inner lining composed of millions of cells. Changes in these cells can lead to growths in the colon that can become cancerous and should be removed.

When the colon lining changes

Changes that happen in the cells that line the colon or rectum can lead to growths called polyps. Over a period of years, polyps can turn cancerous. Removing polyps early may prevent cancer from ever forming.

  • Polyps are fleshy clumps of tissue that form on the inner lining of the colon or rectum. Small polyps are usually benign (not cancerous). However, over time, cells in a type of polyp known as an adenomatous polyp (also called an adenoma) can change and become cancerous. The longer a polyp is there and the larger a polyp grows, the more likely this is to happen. 

  • Colorectal cancers usually start when polyp cells begin growing abnormally. As a cancerous tumor grows, it can invade into the deeper layers of the colon or rectal wall. In time, cancer can grow beyond the colon or rectum and into nearby organs or it can spread to nearby lymph nodes. The cancer cells can also travel to other parts of the body. This is known as metastasis. The earlier a cancerous tumor is removed, the better the chance of preventing its spread.

Treatment choices for colon and rectal cancer

You and your healthcare provider will discuss a treatment plan that’s best for your needs.

  • Surgery is often done to remove the cancerous parts of the colon and rectum. Some surrounding tissue is removed as well, possibly including nearby lymph nodes.

  • Chemotherapy may be done in addition to surgery, or instead of surgery if the cancer is advanced. This therapy uses medicines to attack cancer cells. It is considered systemic therapy because it works throughout the body. It's usually done as an outpatient procedure in a healthcare provider's office, clinic, or hospital. You may receive the medicine in pill form or through an IV line or infusion pump (a device that slowly releases medicine into your bloodstream).

  • Radiation therapy may be done, especially for rectal cancer. This treatment uses high-energy X-rays to kill cancer cells. It’s considered localized therapy because it targets the specific area of the body affected by the cancer. It is usually performed on an outpatient basis in a hospital or radiation clinic.

  • Targeted therapy uses drugs that target proteins or cell functions that help cancer cells grow. Some of these drugs are given along with chemotherapy drugs, while others are used by themselves. 

Online Medical Reviewer: Alteri, Rick, MD
Online Medical Reviewer: Image reviewed by StayWell medical illustration team.
Online Medical Reviewer: MMI board-certified, academically affiliated clinician
Last Review Date: 11/1/2015
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