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Patient education: Screening for colorectal cancer (Beyond the Basics)

Patient education: Screening for colorectal cancer (Beyond the Basics)
Chyke Doubeni, MD, FRCS, MPH
Section Editors:
Joann G Elmore, MD, MPH
Kenneth K Tanabe, MD
Deputy Editor:
Jane Givens, MD, MSCE
Literature review current through: Nov 2022. | This topic last updated: Oct 22, 2021.

COLORECTAL CANCER SCREENING OVERVIEW — Colorectal cancer is the term for cancer of the colon (large intestine) or rectum (figure 1). (See "Patient education: Colon and rectal cancer (Beyond the Basics)".)

The primary goal of colorectal cancer screening is to prevent deaths from colorectal cancer. Screening tests can help identify cancers at an early and potentially curable stage. Screening can also prevent cancer by identifying and treating precancerous abnormal growths that can be removed before they become malignant.

Adults should undergo colorectal cancer screening beginning at age 45 or earlier, depending upon their risk of developing colorectal cancer. Several tests are available, each of which has advantages and disadvantages. The optimal screening test depends upon your preferences and your risk of developing colorectal cancer.

This article discusses colorectal cancer risks, available screening tests, and recommendations for screening based upon your risks. Additional topics are discussed separately, including the screening tests themselves (see "Patient education: Colonoscopy (Beyond the Basics)" and "Patient education: Flexible sigmoidoscopy (Beyond the Basics)") as well as specific conditions (see "Patient education: Colon polyps (Beyond the Basics)" and "Patient education: Crohn disease (Beyond the Basics)" and "Patient education: Ulcerative colitis (Beyond the Basics)").

WHY COLORECTAL CANCER SCREENING WORKS — Most colorectal cancers develop from precancerous polyps. Polyps are growths that form in the lining of the colon. They can be detected with an endoscopic procedure (colonoscopy or sigmoidoscopy) or CT colonography (see 'Colonoscopy' below and 'Sigmoidoscopy' below and 'CT colonography' below) and, to a lesser extent, by other tests such as the stool test for colorectal cancer. (See 'Stool tests' below.)

The two most commonly detected types of polyps are "adenomatous" and "hyperplastic." Adenomatous polyps (also called adenomas) can become cancerous over time; this progression takes at least 10 years in most people. (See "Patient education: Colon polyps (Beyond the Basics)".)

Colorectal cancer screening tests can detect polyps and cancers. If a polyp is found, it is removed to try to prevent it from becoming more serious. Regular screening for and removal of polyps reduces your risk of developing colorectal cancer (by up to 90 percent with colonoscopy). Similarly, if a cancer is found, it may be treated, hopefully at an earlier stage than it would have been found otherwise. Early detection of cancers that are already present in the colon increases the chance of successful treatment and decreases the chance of dying as a result of the cancer.

COLORECTAL CANCER RISK FACTORS — The risk of colorectal cancer increases as a person gets older. This is why experts recommend screening for people who are age 45 or older, even if the person does not have additional risk factors. (See 'Colorectal cancer screening plans' below.)

Some people have additional factors that increase their risk of colorectal cancer. Some of these impact recommendations for when to begin screening, while others do not.

Risk factors that may affect screening recommendations — Some conditions significantly increase a person's risk of colorectal cancer. Doctors often recommend that people with these conditions begin colorectal cancer screening earlier than people considered to be at average risk. (See 'Increased risk of colorectal cancer' below.)

Genetic familial syndromes — While uncommon, certain syndromes that are passed down in families can increase a person's risk of developing colorectal cancer. They include:

Familial adenomatous polyposis (FAP) – FAP is an uncommon inherited condition in which hundreds of polyps (or more) develop throughout the colon beginning in adolescence. Nearly all people with this condition will develop colorectal cancer during their lifetime, and most of these cancers occur before the age of 45 years.

Lynch syndrome (also known as hereditary nonpolyposis colorectal cancer [HNPCC]) – Lynch syndrome is another inherited condition associated with an increased risk of colorectal cancer. It is slightly more common than FAP but is still uncommon, accounting for less than 1 in 20 cases of colorectal cancer. About 70 percent of people with Lynch syndrome will develop colorectal cancer by the age of 65. Cancer also tends to occur at younger ages. People with Lynch syndrome are also at risk for other types of cancer, including cancer of the uterus, stomach, bladder, kidney, and ovary.

There are other rarer inherited conditions that increase risk of colorectal cancer, including mutY DNA glycosylase gene (MUTYH)-associated polyposis, hamartomatous polyposis, Peutz-Jeghers syndrome, and juvenile polyposis syndrome.

If any of these conditions run in your family, you can get genetic testing to find out whether you have the abnormal gene.

Personal or family history of colorectal cancer or polyps — People who have previously had colorectal cancer have an increased risk of developing a new colorectal cancer. People who have had adenomatous polyps before the age of 60 years are also at increased risk for developing colorectal cancer.

Having a first-degree relative (a parent, brother or sister, or child) with colorectal cancer increases your risk of developing colorectal cancer. In addition, having a relative who had adenomatous polyps is also believed to increase your risk. Your risk may be further increased depending on how many family members are affected and the age at which their cancer or polyps were detected.

Inflammatory bowel disease — People with Crohn disease or ulcerative colitis have an increased risk of colorectal cancer. The amount of increased risk depends upon the amount of inflamed colon and the duration of disease; pancolitis (inflammation of the entire colon) and colitis of 10 years' duration or longer are associated with the greatest risk for colorectal cancer. (See "Patient education: Crohn disease (Beyond the Basics)" and "Patient education: Ulcerative colitis (Beyond the Basics)".)

Lifestyle risk factors — Certain lifestyle factors also seem to increase a person's risk of developing colorectal cancer. These include:

A diet high in fat and red or processed meat and low in fiber

A sedentary lifestyle

Cigarette smoking

Alcohol use


Modifying these risk factors may help lower your risk of colorectal cancer, in addition to improving your overall health. However, the presence of these risk factors does not generally impact expert recommendations for when to begin colorectal cancer screening.

Factors that may decrease risk — As discussed above, improving your diet, increasing physical activity, cutting back on alcohol, and quitting smoking (if you smoke) can all help lower your risk of developing colorectal cancer.

Using aspirin for prevention of cardiovascular disease may also decrease the risk of developing colorectal cancer, but this should be discussed with your doctor to understand the benefits and risks of taking aspirin. Because taking aspirin regularly comes with risks of its own, it's a good idea to talk with your health care provider before trying this. (See "Patient education: Aspirin in the primary prevention of cardiovascular disease and cancer (Beyond the Basics)", section on 'Colorectal cancer'.)

TESTS USED FOR COLORECTAL CANCER SCREENING — Several tests available for colorectal cancer screening can detect precancerous polyps (adenomas) and can lead to cancer prevention and/or detect cancers at an early, more treatable stage.

Guidelines from expert groups recommend that you and your health care provider discuss the available options and choose a testing strategy that works best for you. Some experts believe that tests that are very good at detecting precancerous polyps are preferable, particularly colonoscopy. Other experts believe that having screening with any of the available tests is more important than which particular test you choose. The recommended frequency of testing varies depending on which test is chosen. (See 'Colorectal cancer screening plans' below.)

Colonoscopy — Colonoscopy allows a clinician to see the lining of the entire colon, including the rectum (figure 1). (See "Patient education: Colonoscopy (Beyond the Basics)".)

Procedure – Colonoscopy requires that you prepare by cleaning out your entire colon so the doctor can see the inside well. This clean out usually involves drinking a laxative liquid preparation that causes temporary diarrhea. During colonoscopy, you may be given a mild sedative drug or some doctors use a stronger anesthetic agent that puts you to sleep. A thin, flexible, lighted tube is inserted through the anus and used to directly inspect the lining of the rectum and the entire colon. Biopsies (samples of tissue) may be taken during the procedure. Polyps and some cancers can be removed during this procedure.

Effectiveness – Colonoscopy is the most sensitive of the available tests; it detects most small polyps and almost all large polyps and cancers and substantially lower the risk of developing and dying from colorectal cancer.

Risks and disadvantages – The risks of colonoscopy, while small, are greater than those of other screening tests. Colonoscopy may lead to serious bleeding or a tear of the intestinal wall in some individuals (about 1 out of every 1000 people). Because the procedure usually requires sedation, you must be accompanied home after the procedure and you should not return to work or other activities on the same day.

Sigmoidoscopy — Sigmoidoscopy allows a clinician to directly view the lining of the rectum and the lower part of the colon (the descending colon) (figure 1). This area accounts for about one-half of the total area of the rectum and colon. Sigmoidoscopy is rarely used in the United States. (See "Patient education: Flexible sigmoidoscopy (Beyond the Basics)".)

Procedure – Sigmoidoscopy requires that you prepare by cleaning out the lower part of your colon. This usually involves consuming a clear liquid diet and using an enema (a solution you insert into your rectum) shortly before the examination. Most people do not need sedative drugs and are able to return to work or other activities the same day. During the procedure, a thin, flexible, lighted tube is inserted into the rectum and into the left side of the colon to check for polyps and cancer; the procedure may cause mild cramping. Biopsies (small samples of tissue) can be taken during sigmoidoscopy. Sigmoidoscopy may be performed in a doctor's office.

Effectiveness – Sigmoidoscopy can identify polyps and cancers in the lower (descending) colon and rectum with a high degree of accuracy. Studies have shown that screening with sigmoidoscopy reduces the chances of getting or dying from colorectal cancer.

Risks and disadvantages – The risks of sigmoidoscopy causing a serious problem are low. The procedure could create a small tear in the intestinal wall in about 2 per every 10,000 people; death from this complication is rare. A major disadvantage of sigmoidoscopy is that it cannot detect polyps or cancers that are located only in the right side (for example, in the cecum or ascending colon to the hepatic flexure) or in the transverse colon, which are more common in older women.

Having polyps or cancers in the lower colon increases the likelihood that there are polyps or cancer in the remaining part of the colon. Thus, if sigmoidoscopy reveals polyps or cancer, colonoscopy is recommended to view the entire length of the colon.

CT colonography — Computed tomography colonography (CTC, sometimes called "virtual colonoscopy") is a test that uses a CT scanner to take images of the entire colon. These images are two- and three-dimensional and are reconstructed to allow a radiologist to determine if polyps or cancers are present (picture 1). The major advantages of CTC are that it does not require sedation, it is noninvasive, the entire bowel can be examined, and abnormal areas (adenomas) can be detected about as well as with traditional (optical) colonoscopy.

There are some disadvantages of CTC. Like traditional colonoscopy, CTC usually requires a "bowel prep" to clean out the colon. If an abnormal area is found with CTC, a traditional colonoscopy will be needed to see the area and take a tissue sample (biopsy). CTC may detect abnormalities other than polyps or cancer in the colon/rectum. Many of these incidental findings will require further testing that could lead to harm. CTC may not be covered by health insurance plans in the United States. CTC, like many other imaging tests, exposes patients to radiation which may have long-term risks.

Stool tests — Colorectal cancers often release microscopic amounts of blood and abnormal DNA into the stool. Stool tests can detect blood or abnormal DNA markers. Although these tests involve collecting stool samples at home, they require a prescription from a doctor.

Two types of tests, fecal occult blood testing (also called guaiac testing, or gFOBT) and fecal immunochemical testing (FIT), evaluate the stool for blood, which may be present if there is bleeding from a colorectal cancer (or other source).

With guaiac testing, you collect two samples of stool from three consecutive bowel movements, which you apply to home collection cards. You mail the cards back according to the instructions. You should avoid drugs that irritate the stomach, such as aspirin and nonsteroidal antiinflammatory drugs (NSAIDs), before collecting the stool.

With fecal immunochemical testing, you use a long-handled tool to collect the specimen according to the manufacturer's instructions. You apply the brush to a kit and then mail the kit back according to instructions. You do not have to change your diet or stop any medications with this test. Immunochemical testing is more convenient and somewhat better able to find cancer than guaiac testing, but the test kit is a bit more expensive.

If a stool test is positive, your entire colon should be examined with colonoscopy.

Stool testing reduces the risk of dying from colorectal cancer. However, because polyps seldom bleed, stool testing for blood is less likely than other screening tests to detect polyps. In addition, "false positives" are common, meaning that many people with a positive stool test will not turn out to have colorectal cancer.

A FIT-DNA test is another option and is done every three years. This test looks for specific DNA markers that may signify the presence of a colorectal cancer, and it also looks for blood in the stool. For this test, you get a special kit in order to collect a whole bowel movement. Then you follow the instructions about how and where to ship it. An abnormal test result should be followed up by colonoscopy.

COLORECTAL CANCER SCREENING PLANS — The screening plan that is right for you depends upon your risk of colorectal cancer. You can talk with your health care provider about when to begin screening, which tests are available, and how often you should be screened. (See 'Colorectal cancer risk factors' above.)

Average risk of colorectal cancer — People with an average risk of colorectal cancer should begin screening at age 45. Any one of the following screening strategies is recommended:

Colonoscopy every 10 years

Stool testing every year (using guaiac or fecal immunochemical occult blood tests)

Computed tomographic colonography (CTC) every five years

Flexible sigmoidoscopy every five years, with or without a fecal immunochemical (FIT) stool test

Stool testing using FIT and DNA testing every one to three years

You and your provider should work together to decide which approach makes the most sense for you based on test availability as well as your preferences and values. For most people, screening should continue until at least age 75, assuming a life expectancy of 10 years or more.

Increased risk of colorectal cancer — Screening for people with an increased risk may entail starting screening at a younger age, more frequent screening, and/or the use of more sensitive screening tests (usually colonoscopy). The optimal screening plan depends upon the reason for increased risk.

Personal history of colorectal cancer — If you have been treated for colorectal cancer in the past, your doctor will talk to you about how often to have screening (as well as other tests and physical exams) to check for recurrence. This typically includes frequent colonoscopies. The exact timing for follow-up visits, including colonoscopies, will depend on your situation and past treatments.

Family history of colorectal cancer — Screening recommendations depend on your family history, including how many relatives were affected, their ages at diagnosis, and whether they had colorectal cancer or advanced polyps such as adenomatous polyps or serrated lesions (a term that refers to the appearance under a microscope).

Doctors recommend early screening (starting at age 40, or 10 years younger than the earliest diagnosis in the family, whichever comes first) for people who have:

One first-degree relative (parent, brother, sister, or child) with colorectal cancer, an advanced adenomatous polyp, or advanced serrated lesion before the age of 60 years – Screening should be repeated with a colonoscopy every five years.

Two or more first-degree relatives with colorectal cancer, an advanced adenomatous polyp, or advanced serrated lesion at any age – Screening should be repeated with a colonoscopy every five years.

One first-degree relative (ie, parent, brother, sister, or child) with colorectal cancer, an advanced adenomatous polyp, or an advanced serrated lesion at the age of 60 years or older – After the initial test, screening should be repeated on the same schedule as for people at average risk (eg, with a colonoscopy every 10 years).

As noted, screening in the above situations usually involves colonoscopy, although annual fecal immunochemical testing may also be an option if you are not willing to start with a colonoscopy. (See 'Colonoscopy' above and 'Stool tests' above.)

People with only a second-degree relative (eg, grandparent, aunt, or uncle) or third-degree relative (eg, great-grandparent or cousin) with colorectal cancer do not have a large enough increase in risk to warrant more screening than is recommended for those at average risk. People with relatives who have had only non-advanced adenomatous polyps are also screened according to recommendations for people at average risk. (See 'Average risk of colorectal cancer' above.)

Genetic familial syndromes — Some people have known genetic syndromes in their family that increase the risk of colorectal cancer, such as familial adenomatous polyposis (FAP) or Lynch syndrome (also known as hereditary nonpolyposis colorectal cancer [HNPCC]) (see 'Genetic familial syndromes' above). These less common conditions require aggressive screening and preventive treatments. If any of these syndromes run in your family, it's important to see an experienced clinician regularly for monitoring and testing.

Inflammatory bowel disease — If you have ulcerative colitis or Crohn disease, you have an increased risk of colorectal cancer. The best screening plan will depend on how long you have had the disease and how much of your colon is affected. (See "Patient education: Crohn disease (Beyond the Basics)" and "Patient education: Ulcerative colitis (Beyond the Basics)".)

WHERE TO GET MORE INFORMATION — Your health care provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our web site ( Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient education: Colon and rectal cancer screening (The Basics)
Patient education: Colonoscopy (The Basics)
Patient education: Cancer screening (The Basics)
Patient education: Colon polyps (The Basics)
Patient education: Familial adenomatous polyposis (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

Patient education: Flexible sigmoidoscopy (Beyond the Basics)
Patient education: Colonoscopy (Beyond the Basics)
Patient education: Colon polyps (Beyond the Basics)
Patient education: Crohn disease (Beyond the Basics)
Patient education: Ulcerative colitis (Beyond the Basics)
Patient education: Colon and rectal cancer (Beyond the Basics)

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

Screening for colorectal cancer: Strategies in patients at average risk
Screening for colorectal cancer in patients with a family history of colorectal cancer or advanced polyp
Tests for screening for colorectal cancer
Surveillance and management of dysplasia in patients with inflammatory bowel disease
Lynch syndrome (hereditary nonpolyposis colorectal cancer): Cancer screening and management
Familial adenomatous polyposis: Screening and management of patients and families
Juvenile polyposis syndrome

The following organizations also provide reliable health information.

National Cancer Institute



The American Society of Clinical Oncology


American Cancer Society



National Library of Medicine


The American Gastroenterological Association


The American College of Gastroenterology


ACKNOWLEDGMENT — The editorial staff at UpToDate would like to acknowledge Robert H Fletcher, MD, MSc, who contributed to an earlier version of this topic review.

The author, Dr. Chyke Doubeni, is a member of the US Preventive Services Task Force (USPSTF). This topic review does not necessarily represent the views and policies of the USPSTF.

This generalized information is a limited summary of diagnosis, treatment, and/or medication information. It is not meant to be comprehensive and should be used as a tool to help the user understand and/or assess potential diagnostic and treatment options. It does NOT include all information about conditions, treatments, medications, side effects, or risks that may apply to a specific patient. It is not intended to be medical advice or a substitute for the medical advice, diagnosis, or treatment of a health care provider based on the health care provider's examination and assessment of a patient's specific and unique circumstances. Patients must speak with a health care provider for complete information about their health, medical questions, and treatment options, including any risks or benefits regarding use of medications. This information does not endorse any treatments or medications as safe, effective, or approved for treating a specific patient. UpToDate, Inc. and its affiliates disclaim any warranty or liability relating to this information or the use thereof. The use of this information is governed by the Terms of Use, available at ©2023 UpToDate, Inc. and its affiliates and/or licensors. All rights reserved.
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