Colon Cancer

What Is Colon Cancer?

There are four stages of colon cancer.
There are four stages of colon cancer.

The human colon, or large intestine, is a muscular, tube-shaped organ measuring about 4 feet long. It extends from the end of the small bowel to the rectum; some doctors may include the rectum as the end of the colon. The term colorectal describes this area that begins at the colon and ends at the anus. Typically, the first or right portion of the colon which is called the ascending colon moves up from the lower right portion of the abdomen. The next portion, or transverse colon, moves across from the right to the left side of the upper abdomen. Next, the third region or descending colon moves down the left side of your abdomen. Then an S shaped or sigmoid colon portion of the large intestine connects the rest of the colon to the rectum, which ends at the anus. This article will focus on the colon and less on the rectum; however, the terms colon, colorectum, and colorectal are considered interchangeable in this general article.

The colon has three main functions:

  • To digest and absorb nutrients from food
  • To concentrate fecal material by absorbing fluid (and dissolved salts, also called electrolytes) from it
  • To store and control evacuation of fecal material

The right side of your colon plays a major role in absorbing water and electrolytes, while the left side is responsible for storage and evacuation of stool.

Cancer is the transformation of normal cells. The transformed cells grow and multiply abnormally.

  • Left untreated, these colon cancers grow and eventually spread through the colon wall to involve the adjacent lymph nodes and organs. Ultimately, the cancer cells spread (metastasized) to distant organs such as the liver, lungs, brain, and bones.
  • Cancers are dangerous because of their unbridled growth and potential for spread. They overwhelm healthy cells, tissues, and organs by taking their oxygen, nutrients, and space.
  • Most colon cancers are adenocarcinomas -- tumors that develop from the glands lining the colon's inner wall.
  • These cancers, or malignant tumors, are sometimes referred to as colorectal cancer, reflecting the fact that the rectum, the end portion of the colon, can also be affected. Anatomic differences in the rectum as compared to the rest of the colon require that these areas be separately recognized by many investigators.

In the United States, one in 23 men and one in 25 women will develop colorectal cancer.

  • According to reports from the American Cancer Society, colorectal cancer is the third most common cancer in U.S. men and women (2020 report that excluded skin cancers).
  • The overall incidence of colorectal cancer increased until 1985 and then began decreasing at an average rate of about 3.6% per year in people 55 and older from 2007-2016 (available data). However, in people younger than 55, colorectal cancer increased by about 2% each year. Actor Chadwick Boseman, star of Black Panther, recently died from a 4-year battle with colon cancer at age 43. Black individuals have a 20% higher rate than non-Hispanic whites; the causes of these differences are under investigation.
  • Deaths from colorectal cancer rank third after lung and prostate cancer for men and third after lung and breast cancer for women.
  • Death statistics from colon cancer vs. rectal cancer is not clear as an estimated 40% of rectal cancers are misdiagnosed as colon cancer (another reason for lumping them together numerically).

What Are Colon Cancer Risk Factors and Causes?

Most colorectal cancers arise from adenomatous polyps. Such polyps are comprised of excess numbers of both normal and abnormal appearing cells in the glands covering the inner wall of the colon. Over time, these abnormal growths enlarge and ultimately degenerate to become adenocarcinomas.

People with certain genetic abnormalities develop what are known as familial adenomatous polyposis syndromes. Such people have a greater-than-normal risk of colorectal cancer.

  • In these conditions, numerous adenomatous polyps develop in the colon, ultimately leading to colon cancer.
  • There are specific genetic abnormalities found in the two main forms of familial adenomatous polyposis.
  • The cancer usually occurs before age 40 years.
  • Adenomatous polyposis syndromes tend to run in families. Such cases are referred to as familial adenomatous polyposis (FAP). Celecoxib (Celebrex) has been FDA approved for FAP. After 6 months, celecoxib reduced the mean number of rectal and colon polyps by 28% compared to placebo (sugar pill) 5%.

Another group of colon cancer syndromes, termed hereditary non-polyposis colorectal cancer (HNPCC) syndromes, also run in families. In these syndromes, colon cancer develops without the precursor polyps.

  • HNPCC syndromes are associated with a genetic abnormality. This abnormality has been identified, and a test is available. People at risk can be identified through genetic screening.
  • Once identified as carriers of the abnormal gene, these people require counseling and regular screening to detect pre-cancerous and cancerous tumors.
  • HNPCC syndromes are sometimes linked to tumors in other parts of the body.

Also at high risk for developing colon cancers are people with any of the following:

The cancer risk increases two to three times for people with a first-degree relative (parent or sibling) with colon cancer. The risk increases more if you have more than one affected family member, especially if the cancer was diagnosed at a young age.

Other factors that may affect your risk of developing a colon cancer:

  • Diet: Whether diet plays a role in developing colon cancer remains under debate. The belief that a high-fiber, low-fat diet could help prevent colon cancer has been questioned. Studies do indicate that exercise and a diet rich in fruits and vegetables can help prevent colon cancer.
  • Obesity: Obesity has been identified as a risk factor for colon cancer.
  • Smoking: Cigarette smoking has been definitely linked to a higher risk for colon cancer.
  • Drug effects: Recent studies have suggested postmenopausal hormone estrogen replacement therapy may reduce colorectal cancer risk by one-third. Patients with a certain gene that codes for high levels of a hormone called 15-PGDH may have their risk of colorectal cancer reduced by one-half with the use of aspirin.

What Are Colon Cancer Symptoms and Signs?

Symptoms of colon cancer may not be present or be minimal and overlooked until it becomes more severe. Colorectal cancer screening tests thus are important in individuals 50 and older. Cancer of the colon and rectum can exhibit itself in several ways. If you have any of these symptoms, seek immediate medical help. You may notice bleeding from your rectum or blood mixed with your stool (poop). It usually, but not always, can be detected through a fecal occult (hidden) blood test, in which samples of stool are submitted to a lab for detection of blood. A home test (screening test) may be available to test for blood in the stool.

  • People commonly attribute all rectal bleeding to hemorrhoids, thus preventing early diagnosis owing to lack of concern over "bleeding hemorrhoids." Bloody stools may be an early sign of colon cancer. New onset of bright red blood in the stool always deserves an evaluation. Blood in the stool may be less evident, and is sometimes invisible, or causes a black or tarry stool.
  • Rectal bleeding may be hidden and chronic and may only show up as an iron deficiency anemia.
  • It may be associated with fatigue and pale skin due to the anemia.
  • Changes in bowel movement frequency
  • It usually, but not always, can be detected through a fecal occult (hidden) blood test, in which samples of stool are submitted to a lab for detection of blood.
  • If the tumor gets large enough, it may completely or partially block your colon. You may notice the following symptoms of bowel obstruction:
    • Abdominal distension: Your belly sticks out more than it did before without weight gain.
    • Abdominal pain: This is rare in colon cancer. One cause is tearing (perforation) of the bowel. Leaking of bowel contents into the pelvis can cause inflammation (peritonitis) and infection. This is usually a late sign of colon cancer.
    • Unexplained, persistent nausea or vomiting
    • Unexplained weight loss
    • Change in frequency or character of stool (bowel movements)
    • Small-caliber (narrow) or ribbon-like stools
    • Constipation
    • Sensation of incomplete evacuation after a bowel movement
    • Rectal pain: Pain rarely occurs with colon cancer and usually indicates a bulky tumor in the rectum that may invade surrounding tissue after moving through the colon's submucosa.

Studies suggest that the average duration of symptoms (from onset to diagnosis) is 14 weeks.

When Should Someone Seek Medical Care for Suspected Colon Cancer?

Any of the following symptoms warrants an immediate visit to your health care provider:

  • Bright red blood on the toilet paper, in the toilet bowl, or in your stool when you have a bowel movement
  • Change in the character or frequency of your bowel movements
  • Sensation of incomplete evacuation after a bowel movement
  • Unexplained or persistent abdominal pain or distension
  • Unexplained weight loss
  • Unexplained, persistent nausea or vomiting

Any of the following symptoms warrants a visit to the nearest hospital emergency department:

  • Large amounts of bleeding from your rectum, especially if associated with sudden weakness or dizziness
  • Unexplained severe pain in your belly or pelvis (groin area)
  • Vomiting and inability to keep fluids down

What Exams and Tests Diagnose Colon Cancer?

If you are having rectal bleeding or changes in your bowel movements, you will undergo tests to determine the cause of the symptoms and signs. If you are not sure you have blood in the stools, you may have a fecal occult blood test (FOBT) where a doctor puts a small sample of your stool on a special card and tests it for the presence of blood.

  • Your health care provider may insert a gloved finger into your rectum through your anus.
  • This test, called a digital rectal exam, is a quick cancer screening to make sure that any bleeding is actually coming from your rectum.
  • This is not painful, but it is mildly uncomfortable for some people. The cancer screening takes only a few seconds.

You may have a test called a colonoscopy.

  • This is a test that allows a specialist in digestive diseases (a gastroenterologist) to look at the inside of your colon.
  • This test looks for polyps, tumors, or other abnormalities.
  • Colonoscopy is an endoscopic test. This means that a thin, flexible plastic tube with a tiny camera on the end will be inserted into your colon via your anus. As the tube is advanced further into your colon, the camera sends images of the inside of your colon to a video monitor.
  • Colonoscopy is usually done with sedation and is not an uncomfortable test for most people. You will first be given a laxative solution to drink that will clear most of the fecal matter from your bowel. You will be allowed nothing to eat for a short period before the test and a liquid diet only for a day before the test.
  • Flexible sigmoidoscopy is similar to colonoscopy but does not go as far into the colon. It uses a shorter endoscope to examine the rectum, sigmoid (lower) colon, and most of the left colon.
  • CT colonography is another way to examine the colon. Again, the stool must be cleared from the colon before the examination. Colonoscopy allows sample to be taken (biopsies) if an abnormality is found. Colonography does not allow that, as there is no direct visualization of the interior of the colon.

Air-contrast barium enema is a type of X-ray that can show tumors.

  • Before the X-ray is taken, a liquid is introduced into your colon and rectum through your anus. The liquid contains barium, which shows up solid on X-rays.
  • This test highlights tumors and certain other abnormalities in the colon and rectum.
  • Other types of contrast enemas are available.
  • Air-contrast barium enema frequently detects malignant tumors, but it is not as effective in detecting small tumors or those far up in your colon.

If a tumor is identified in the colon or rectum by a biopsy performed during a sigmoid or colonoscopy, you will probably undergo CT scan of your abdomen and a chest X-ray to make sure the disease has not spread to other parts of the body.

How Do Doctors Determine the Stage of Colon Cancer?

Tumor spread determines the staging. However, there are other staging methods that doctors use, and those systems are similar to the 0-4 staging system described below:

  1. Stage 0: abnormal colon cells on the mucosa
  2. Stage 1: cancer cells invaded the mucosa and submucosa
  3. Stage 2: cancer cells spread past the colon wall but not affecting the lymph nodes (can be subdivided into stages A, B, C, with C as most advanced)
  4. Stage 3: cancer cells spread past the colon lining and into the lymph nodes (can be subdivided into stages A, B, C, with C as most advanced)
  5. Stage 4: cancer cells have spread to other organs

What Are Medical and/or Surgical Treatments for Colon Cancer?

Polyps, if suggestive of being either cancer-related or cancer-specific in appearance and if few in number, may be removed during colonoscopy (polypectomy) as initial colon cancer treatment.

Although the primary treatment of colon cancer is to surgically remove part of your colon or all of it (colectomy) in some patients, chemotherapy after surgery can improve your likelihood of being cured if your colon cancer has spread to nearby lymph nodes (metastatic colon cancer).

Radiation treatment or radiation therapy after surgery does not improve cure rates in people with colon cancer, but it is important for people with rectal cancer.

  • Given before surgery, radiation therapy may reduce tumor size. This can improve the chances that the tumor will be removed successfully.
  • Radiation before surgery also appears to reduce the risk of the cancer coming back after treatment.
  • Radiation plus chemotherapy before or after surgery for rectal cancer can improve the likelihood that the treatment will be curative.

Surgery for Colon Cancer

Surgery is the cornerstone of treatment for bowel cancer.

  • Sometimes only a polyp is found to be cancerous, and removal (polypectomy) of the polyp may be all that is necessary.
  • You will usually only need to have a portion of your colon removed for colon cancer. In rare circumstances such as in longstanding ulcerative colitis or in cases where large numbers of polyps are found, then the entire colon may need to be removed. Most colon cancer surgery will not result in a colostomy (piece of colon is diverted and opens through portion of the abdominal wall) being necessary as the bowel having been cleaned out prior to surgery can then safely be reconnected (resection) after a portion is removed. In rectal cancer sometimes, a colostomy is necessary if it is not safe or feasible to reconnect the portions of the rectum and anus that remain after the cancer involved area is removed.
  • Surgery may also be done to relieve symptoms in advanced cancer such as when the cancer has caused a bowel obstruction. The usual procedure is bypass for obstructions that cannot be cured. Rarely a colon cancer presents with such severe blockage (obstruction) or is so massive that a resection cannot be done. Usually then a colostomy is formed after which other treatment is planned.

Sometimes a colorectal tumor can be surgically removed only by creation of a permanent colostomy.

  • This is a small, neatly constructed opening in your belly. As part of the surgery, the colon that is left in your body is attached to this opening.
  • Fecal matter will exit your body through this hole instead of through your anus.
  • You will wear a small appliance or bag, which attaches to your skin around the opening and collects fecal matter. The bag is changed regularly to prevent skin irritation and odor.
  • Your surgeon will attempt to preserve your rectum and anus whenever possible. Several surgical procedures have been developed that can preserve evacuation of fecal material through the anus whenever possible.

Whether you need a colostomy depends on individual circumstances.

  • In general, tumors on the right side of your colon or on the left side above the level of the rectum may not call for colostomy.
  • Tumors in the rectum may require removal of the rectum and anal sphincter and construction of a permanent colostomy to divert your bowel.

In addition, some patients with metastatic colorectal cancer may undergo either radiofrequency or cryoablation procedures. These procedures are designed to remove or kill most of or all of the tumor and save the function of most of the remaining organ tissue (for example, liver or lung tissue).

Targeted Therapy

Targeted therapy is a treatment that uses drugs or other substances to attack specific cancer cells. Monoclonal antibodies can be used alone or carry drugs to damage or kill specific cancer cells. Other compounds like bevacizumab and ramucirumab harm cancer cells by inhibiting the cancer's formation of blood vessels. Substances like cetuximab and panitumumab inhibit or stop cancer cell growth. Ziv-aflibercept and regorafenib are angiogenesis inhibitors that stop the growth of new blood vessels needed for tumor growth. Side effects may include diarrhea and liver, skin, and lung problems.


Immunotherapy is treatment that uses the person's immune system to disable or kill cancer cells. For example, a protein termed PD-L1 on tumor cells binds with PD-1 on a patient's normal T killer cells to inhibit the killing of tumor cells. An immune checkpoint inhibitor like pembrolizumab can bind to the PD-L1 tumor protein and allow a person's T killer cells to attack the tumor cancer cells. Side effects may include diarrhea, skin changes, breathing problems and pain.

What Follow-up Is Needed After Colon Cancer Treatment?

Once your cancerous colon has been removed and you receive any other treatment recommended by your cancer care team, you will see your gastroenterologist or cancer specialist (oncologist) regularly for follow-up visits. These visits will allow your team to see if the cancer has spread and to detect newly formed cancers.

These follow-up visits should include, at minimum, the following:

  • Colonoscopy within 3 months after your surgery
  • Colonoscopy 1 year after surgery and every 3 years after that.
  • Test for occult (hidden) blood in your stool every year, followed by colonoscopy if the test result is positive

An immunochemical screening tool-measurement of carcinoembryonic antigen (CEA) level-is available to test for cancer recurrence following cancer surgery.

  • CEA is a protein normally found in trace amounts in your bloodstream but is present in increased amounts in people with colon cancer. It is referred to as a tumor marker.
  • Blood CEA levels should be measured before colon cancer surgery and then, if elevated prior to surgery, it is appropriate to test it at intervals of 2-3 months for a time after surgery.
  • Increasing levels of serum CEA may indicate that colon cancer has come back and that you should seek further evaluation.
  • Once you have had several blood tests with negative results, you probably don't need to continue the tests indefinitely. However, no one is sure how long you should continue to have the tests.
  • You should discontinue screening tests if you develop new severe health problems that would make you unfit to undergo treatment for a recurrence of your colon cancer.

Is It Possible to Prevent Colon Cancer?

Your best prevention is to detect bowel cancer early and treat it early in its formation. People who have regular screening for colon cancer, including fecal occult blood tests, a sigmoidoscopy or colonoscopy, and polyp removal, greatly reduce their risk of having a colorectal cancer.

Other things you can do to lower your risk include the following:

  • Quit smoking. Smoking cigarettes has been clearly linked with higher risk of colon cancer (as well as many other conditions).
  • Take an aspirin or baby aspirin every day. Because of potential side effects, this is not recommended for everyone. Talk to your health care professional first.
  • Take a safe dose of folic acid (for example, 1 mg) every day.
  • Engage in physical activity every day.
  • Eat a variety of fruits and vegetables every day.

The U.S. Agency for Health Care Policy and Research recommends screening for colon cancer in people older than 50 years who have an average risk for the disease and in people aged 40 years and older who have a family history of colorectal cancer. The agency recommends that one of the following screening techniques be used:

  • Fecal occult blood testing (a screening test) every year combined with flexible sigmoidoscopy every 5 years
  • Double-contrast barium enema every 5-10 years
  • Colonoscopy every 10 years: Colonoscopy remains the most sensitive test for detecting colon polyps and tumors.

Once polyps have been identified, they should be removed. After you have had polyps, even one polyp, you should begin to have more frequent colonoscopies.

Appropriate preventive screening for people with ulcerative colitis includes the following:

  • Colonoscopy every 1-2 years in the following cases:
    • If you have known you have the disease for 7-8 years
    • If the cancer involves the entire colon
    • Beginning 12-15 years after the diagnosis of left-sided colitis
  • Random colon biopsies taken during colonoscopy

In people with ulcerative colitis in whom biopsies show premalignant changes, it is recommended they undergo surgical removal of their colons.

What Are Colon Cancer Survival Rates by Stage?

The following are estimated colon cancer survival rates (percentage of patients who survive at least for at least 5 years after diagnosis) by stage:

  • Stage 1: 92%
  • Stage 2: 80%
  • Stage 3: 65%
  • Stage 4: 14%

These survival rates are based on past history of patients. However, each patient is unique and survival rates are estimates and do not include the most recent data.

What Is the Prognosis of Colon Cancer?

Recovery from colon cancer depends on the extent of your disease before your surgery.

Colon Cancer Survival Rates?

A survivability rate estimates the likelihood of surviving the cancer over time.

  • If your tumor is limited to the inner layers of your colon, you can expect to live free of cancer recurrence 5 years or more 80%-95% of the time depending on how deeply the cancer was found to invade into the wall.
  • If cancer has spread to your lymph nodes adjacent to the colon, the chance of living cancer free for 5 years is 30%-65% depending upon the depth of invasion of the primary tumor and the numbers of nodes found to have been invaded by colon cancer cells.
  • If the cancer has already spread to other organs, the 5-year survival rate drops to 10%-15%.
  • If the cancer has reached your liver but no other organs, removing part of your liver may prolong your life with as many as 20%-40% of patients living cancer free for 5 years after such surgery.
  • The use of non-steroidal anti-inflammatory drugs in long-term colorectal survivors is associated with an approximate 25% reduction in mortality, thus increasing life expectancy.

Colon Cancer Support Groups and Counseling

Living with cancer presents many new challenges, both for you and for your family and friends.

  • You will probably have many worries about how the cancer will affect you and your ability to "live a normal life," that is, to care for your family and home, to hold your job, and to continue the friendships and activities you enjoy.
  • Many people feel anxious and depressed. Some people feel angry and resentful; others feel helpless and defeated.

For most people with cancer, talking about their feelings and concerns helps.

  • Your friends and family members can be very supportive. They may be hesitant to offer support until they see how you are coping. Don't wait for them to bring it up. If you want to talk about your concerns, let them know.
  • Some people don't want to "burden" their loved ones, or prefer talking about their concerns with a more neutral professional. A social worker, counselor, or member of the clergy can be helpful if you want to discuss your feelings and concerns about having cancer. Your primary care doctor or oncologist should be able to recommend someone.
  • Many people with cancer are profoundly helped by talking to other people who have cancer. Sharing your concerns with others who have been through the same thing can be remarkably reassuring. Support groups of people with cancer may be available through the medical center where you are receiving your treatment. The American Cancer Society also has information about support groups all over the United States.

Are There Clinical Trials for Colon Cancer?

There are ongoing clinical trials for therapeutic efficacy and other components related to metastatic colorectal cancer. You and your medical team should discuss if you could qualify for such clinical trials and if such a trial would be of benefit to treating your bowel cancer.

Where Can People Find More Information on Colon Cancer?

For more information about support groups, contact the following agencies:

  • American Cancer Society - (800) ACS-2345
  • National Cancer Institute, Cancer Information Service - (800) 4-CANCER [(800) 422-6237)]; TTY (for deaf and hard of hearing callers) (800) 332-8615

American Cancer Society

American Gastroenterological Association

National Institutes of Health, National Cancer Institute

Pictures of Colon Cancer

Media file 1: Photograph taken through a colonoscope of a tumor in the sigmoid colon. The central area of the tumor is ulcerated and was chronically bleeding, which resulted in a severe anemia. Biopsies confirmed that the tumor was an adenocarcinoma.

Photograph taken through a colonoscope of a tumor in the sigmoid colon.
Photograph taken through a colonoscope of a tumor in the sigmoid colon.

This air contrast barium enema demonstrates two colon cancers occurring in the same patient. Both tumors demonstrate a typical apple core appearance. One can be seen on the right side of the colon in the ascending colon while the second tumor can be seen in the left upper abdomen in an area defined as the splenic flexure. Reproduced with permission from Dr. Isaac Hassan from Colon, Adenocarcinoma, Section of Gastroenterology, Textbook of Radiology, eMedicine.

This air contrast barium enema demonstrates 2 colon cancers occurring in 
the same patient
This air contrast barium enema demonstrates two colon cancers occurring in the same patient

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Colon Cancer Causes

Colon Polyps

Colon polyps usually are benign, slow-growing tumors that arise from the epithelial cells in the large intestine. Some colon polyps contain and/or become cancerous tumors (malignant <1%). Benign colon polyps do not invade nearby tissue or spread to other parts of the body. They are commonly present in many individuals and increase in numbers with increasing age.

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United States. National Cancer Institute. "Colon Cancer Treatment (PDQ®) -- Patient Version." Aug. 21, 2020. <>.