Colon Cancer Information, Facts and Resources

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Cancer can begin in either the colon or the rectum. It may be called colon cancer or rectal cancer, based on where it started. Sometimes physicians refer to these cancers together as colorectal cancer.

This is how your colon and rectum work:

  • As you eat, your stomach secretes gastric juices that break down your food. The food and gastric juices mix into a thick fluid that empties into your small intestine.
  • Your small intestine breaks down the food further. It absorbs most of the nutrients and joins your colon.
  • Your colon absorbs water and nutrients from your food. It also stores waste before the waste exits through your rectum and anus.
  • Together your colon and rectum form your large intestine. The upper 5 to 6 feet of the large intestine are the colon, and the lower 6 inches or so are the rectum.

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Cancer Development

In most cases, colon cancers develop slowly over many years. Most of these cancers begin as a growth of tissue called a polyp in the inner lining of the colon. Usually, polyps bulge into the colon; some are flat, also called sessile. 

  • Polyps are common in people over 45.  
  • Most polyps are benign (noncancerous). But some may turn into cancer.  
  • Removing a polyp early may prevent it from turning into cancer. 
  • Certain kinds of polyps are more likely to become cancerous, especially adenomatous polyps (also called adenomas) and larger polyps. Adenomas have a high chance of turning into cancers called adenocarcinomas.

Types of Colon Cancer

There’s more than one type of colon cancer, but most people with colon cancer have a single type: adenocarcinoma. At Fred Hutch Cancer Center, our colon cancer care team treats all types of the disease.

Adenocarcinomas

More than 95% of colorectal cancers are adenocarcinomas. Adenocarcinomas can form in many parts of the body. They start in tissue that contains glands. Glands are small organs that make and release substances, like hormones, digestive juices or mucus. The colon has glands that make mucus to protect the inner lining of the colon and lubricate it so stool can move through.

Other Rarer Types of Colon Cancer 

Rare types of colorectal cancers include: 

  • Gastrointestinal carcinoid tumors: These tumors start in neuroendocrine cells, which are in many digestive organs. Neuroendocrine cells are similar to both nerve cells and cells that make hormones.
  • Gastrointestinal stromal tumors: These tumors start in a special type of cell that signals your gastrointestinal tract to move food or waste forward in the system.
  • Lymphomas: These cancers start in white blood cells called lymphocytes.

Understanding Colon Cancer

Stages

The treatment that your Fred Hutch care team will recommend for colorectal cancer will be based in part on the stage of your cancer. The stage depends on: 

  • How deep the cancer has spread through the wall of your colon 
  • Whether the cancer has spread to lymph nodes around your colon 
  • Whether the cancer has spread to other parts of your body, such as your liver or lungs 

Colon cancers are grouped into stages I (1) through IV (4), with stage I being the least advanced and stage IV being the most advanced.

Learn About Stages of Colon Cancer

Symptoms

The symptoms of colon cancer, like a change in bowel habits or blood in the stool, are not specific to this disease. Other conditions (that aren’t cancer at all) may cause the same symptoms. If you have any concerns about your bowel health, or your health in general, start by letting your primary care provider know. They can ask you questions, do an exam and order any tests needed to tell what’s happening in your body and why. 

It’s possible to have colon cancer without any symptoms, especially in the early stages. In fact, colon cancer can be growing for years before symptoms appear. That’s why screening tests, like colonoscopy, are important — to check for signs of disease even in people who feel fine.

Read About Colon Cancer Symptoms

Prevention and Risk Factors

The best way to prevent colon cancer is to have a colonoscopy. This lets a physician find and remove polyps before they have a chance to turn into cancer. 

It’s also helpful to know about the many factors that might raise your risk for colon cancer. Some are things you can’t control. But they may help your health care team decide how early you should start being screened and how often. Others are things you do have some control over, like your diet and exercise choices. 

Learn About Prevention and Risk Factors

Screening and Diagnosis

Colonoscopy is the gold standard for screening for colon cancer, and it’s a key tool in diagnosis. But there are several other screening methods, like stool tests that you can do at home. Each screening option has pros and cons. The most important thing is to choose one of the recommended methods and do it. Your primary care provider can help you figure out which method is best for you.

The typical age to start screening is 45 years old. But, if you have a family history of colon cancer, your provider may recommend you start screening at a younger age or get screened more often. If anyone in your family had colorectal cancer or adenoma-type polyps, you should get a colonoscopy rather than use one of the other methods.

Read About Screening Options

Colon Cancer FAQ

There are many similarities between colon cancer and rectal cancer. For example, most of these cancers are of the same type, called adenocarcinoma. Many of the risk factors, signs and symptoms, and diagnostic tests for the two diseases are the same. But there are some differences in the ways that early-stage colon and rectal cancers are usually treated. Learn more about rectal cancer.

If you have any signs or symptoms that you worry might be from colon cancer, talk with your primary care provider. Usually, these symptoms are caused by something else, like an infection, hemorrhoids or inflammatory bowel disease. If you are due for colorectal cancer screening and have symptoms, it is very important that you have a colonoscopy to see if there is a cancer in your colon. Whatever the cause, it’s important to find out so you can get treatment to help. If it is cancer, finding it earlier may mean it’s easier to treat.

Ask your primary care provider to help you understand the best colon cancer screening plan for you.

  • Are any colon cancer screening tests recommended for me? 
  • Do I have more than one screening option? If so, which type of screening should I have?  
  • How often should I have the test? 
  • At what age should I stop having it?
  • What is the purpose of the test? What will the results tell us?

Your provider can also explain details like how to prepare for your screening, what happens during the screening, how you’ll get the results and what to do next. (Adapted from the National Cancer Institute.)

Colon cancer starts when cells in the colon grow out of control. Normally, cells in the body grow and multiply to form new cells as the body needs them. When cells get old or damaged, they die and are replaced. Sometimes, this normal process breaks down. Abnormal or damaged cells grow and multiply when they shouldn’t, forming tumors. Some tumors are cancer, and others are benign (noncancerous).

Colon cancer spreads by growing into, or invading, nearby tissues. If the cancer cells invade nearby lymph nodes or blood vessels, they can travel through the lymph or blood to distant parts in the body. Then they can form new tumors in these places. (Adapted from the National Cancer Institute.)

When physicians and scientists talk about cancer survival rates, they typically mean the percentage of people expected to survive their cancer for at least five years after being diagnosed. (The rate doesn’t include the risk of dying during that time for some other reason.) Overall, the relative five-year survival rate for colon cancer in the U.S. is 65%, according to the National Cancer Institute. 

This rate comes from looking at a large, diverse group of people. The chance of surviving cancer at least five years can vary greatly from one person to another. It depends on many factors, like how far the cancer has spread. Your Fred Hutch care team can explain how statistics like survival rates might apply to you. 

Learn more about colon cancer survival rates.