Colon cancer starts in the cells lining your large intestine

Colon cancer is a disease in which malignant (cancerous) cells form in the lining of your colon, which is the last part of your large intestine. The cancer usually develops slowly over several years, often starting as a small growth called a polyp. Most polyps never become cancer, but some do. If a polyp is found and removed before it turns cancerous, colon cancer can be prevented.

Your colon's job is to absorb water and nutrients from food and to store waste until it leaves your body. When cancer develops there, the cancer cells can grow into the wall of the colon or spread to nearby lymph nodes and other organs. Colon cancer is one of the most common cancers in the United States, but it is also one of the most preventable when caught early.

Key Takeaways

  • Colon cancer develops from polyps in the lining of your colon and usually grows slowly over years.
  • Most people with early colon cancer have no symptoms, which is why screening is important.
  • Screening tests like colonoscopy can find polyps and remove them before they become cancer.
  • Risk factors include age over 45, family history, inflammatory bowel disease, and certain lifestyle factors like smoking and heavy alcohol use.
  • Treatment depends on the stage of cancer and may include surgery, chemotherapy, radiation, or a combination of these.

Who is at higher risk for colon cancer

Your risk of colon cancer increases with age. Most cases occur in people over 50, though colon cancer can happen at any age. If you have a parent, sibling, or child who had colon cancer, your risk is higher. The risk is even greater if that relative was diagnosed before age 50 or if multiple family members had it.

Other risk factors include having inflammatory bowel disease (such as Crohn's disease or ulcerative colitis), a personal history of polyps or colon cancer, smoking, heavy alcohol use, obesity, and a diet high in red or processed meat. People of African American descent have higher rates of colon cancer and tend to be diagnosed at later stages. Having one or more risk factors does not mean you will definitely get colon cancer, but it means screening is especially important.

Early signs and symptoms

Many people with early colon cancer have no symptoms at all. This is why screening is so important—it can find cancer before you feel sick. When symptoms do appear, they may include a change in bowel habits (such as diarrhea, constipation, or narrower stools lasting more than a few weeks), blood in or on your stool, persistent abdominal discomfort (such as cramps, gas, or pain), a feeling that your bowel does not empty completely, or unexplained weight loss.

These symptoms can also be caused by other conditions, such as hemorrhoids, irritable bowel syndrome, or infections. Having symptoms does not mean you have cancer, but you should see a doctor if any of these changes last more than a few weeks. The sooner colon cancer is found, the easier it is to treat.

How doctors screen for and diagnose colon cancer

Screening means looking for cancer in people who have no symptoms. The most common screening test is a colonoscopy, in which a doctor uses a long, thin tube with a camera to look inside your entire colon. If the doctor sees a polyp, they can remove it right away. Other screening options include a fecal immunochemical test (FIT), which checks a stool sample for blood, or a CT colonography (virtual colonoscopy), which uses imaging to look at your colon.

If screening finds something abnormal, or if you have symptoms, your doctor may order a biopsy—removing a small piece of tissue to examine under a microscope. Blood tests and imaging tests like CT scans or MRI may also be used to see if cancer has spread. Once cancer is diagnosed, more tests determine the stage of the cancer (how far it has spread), which guides treatment decisions.

Stages of colon cancer and what they mean

Colon cancer is staged from 0 to 4. Stage 0 means cancer is found only in the innermost lining of the colon. Stage 1 means cancer has grown through the lining into the muscle layer but has not spread to lymph nodes. Stage 2 means cancer has grown through the muscle layer or into nearby tissue but still has not reached lymph nodes. Stage 3 means cancer has spread to nearby lymph nodes but not to distant organs. Stage 4 means cancer has spread to distant organs such as the liver or lungs.

The stage determines treatment options and prognosis (the likely outcome). Earlier stages generally have better outcomes, especially if the cancer is caught before it spreads. Your doctor will explain your stage and what it means for your treatment plan.

Treatment options for colon cancer

Treatment depends on the stage of cancer and your overall health. Surgery is the main treatment for most colon cancers. The surgeon removes the part of the colon containing the cancer and nearby lymph nodes, then reconnects the healthy parts. For early-stage cancers found during screening, sometimes removing the polyp during colonoscopy is enough.

Chemotherapy uses drugs to kill cancer cells and may be given before surgery (to shrink the tumor), after surgery (to kill any remaining cells), or for advanced cancer. Radiation therapy uses high-energy beams to kill cancer cells and is less commonly used for colon cancer than for some other cancers. Newer treatments called targeted therapy and immunotherapy work in different ways and may be used for certain types of colon cancer. Your doctor will discuss which treatments are right for you based on your specific situation.

Life after colon cancer treatment

After treatment ends, you will need follow-up care to watch for signs that cancer has returned. This usually includes regular office visits, blood tests, and imaging tests on a schedule your doctor recommends. The schedule is more frequent at first and may space out over time. You may also need colonoscopy to check for new polyps or cancer.

Many people live for years after colon cancer treatment, and some are cured. Lifestyle changes can help reduce the risk of cancer returning or developing again. These include eating a diet rich in vegetables and whole grains, limiting red and processed meat, staying physically active, maintaining a healthy weight, not smoking, and limiting alcohol. Your doctor or a counselor can help you make these changes.

Frequently Asked Questions

Can colon cancer be prevented?

Colon cancer cannot always be prevented, but the risk can be reduced. Regular screening starting at age 45 (or earlier if you have risk factors) can find and remove polyps before they become cancer. Eating a healthy diet, exercising, maintaining a healthy weight, not smoking, and limiting alcohol also lower your risk.

What is the difference between a polyp and colon cancer?

A polyp is a small growth in the lining of your colon. Most polyps are not cancer and never become cancer. However, some types of polyps can develop into cancer over time. This is why removing polyps during screening is important—it prevents cancer from developing.

Does colon cancer run in families?

Colon cancer can run in families, especially if a family member was diagnosed before age 50 or if multiple relatives had it. If you have a family history of colon cancer, talk to your doctor about when to start screening and whether genetic testing might be right for you.

What should I do if I have symptoms like blood in my stool?

See your doctor. Blood in your stool can have many causes, including hemorrhoids or polyps, but it should always be checked out. Your doctor can examine you and order tests to find out what is causing the symptom.

How long does colon cancer treatment take?

Treatment length varies depending on the stage and type of cancer and the treatments used. Surgery may take a few hours, but recovery takes weeks. Chemotherapy is often given in cycles over several months. Your doctor will explain the timeline for your specific treatment plan.