What is screening?
General Information About Colorectal Cancer
Colorectal Cancer Screening
Risks of Colorectal Cancer Screening
Get More Information From NCI
Changes to This Summary (07/12/2007)
Questions or Comments About This Summary
About PDQ

What is screening?

Screening is looking for cancer before a person has any symptoms. This can help find cancer at an early stage. When abnormal tissue or cancer is found early, it may be easier to treat. By the time symptoms appear, cancer may have begun to spread.

Scientists are trying to better understand which people are more likely to get certain types of cancer. They also study the things we do and the things around us to see if they cause cancer. This information helps doctors recommend who should be screened for cancer, which screening tests should be used, and how often the tests should be done.

It is important to remember that your doctor does not necessarily think you have cancer if he or she suggests a screening test. Screening tests are given when you have no cancer symptoms. Screening tests may be repeated on a regular basis.

If a screening test result is abnormal, you may need to have more tests done to find out if you have cancer. These are called diagnostic tests.

Refer to the following PDQ summaries for information about prevention, diagnosis, and treatment of colorectal cancer:

• Prevention of Colorectal Cancer ¹
• Colon Cancer Treatment ²
• Rectal Cancer Treatment ³

General Information About Colorectal Cancer

Key Points for This Section

Colorectal cancer is a disease in which malignant (cancer) cells form in the tissues of the colon or the rectum. Colorectal cancer is the second leading cause of death from cancer in the United States. Age and health history can affect the risk of developing colon cancer.

Colorectal cancer is a disease in which malignant (cancer) cells form in the tissues of the colon or the rectum.

The colon and rectum are parts of the body's digestive system. The digestive system removes and processes nutrients (vitamins, minerals, carbohydrates, fats, proteins, and water) from foods and helps pass waste material out of the body. The digestive system is made up of the mouth, throat, esophagus, stomach, and the small and large intestines. The first 6 feet of the large intestine are called the large bowel or colon. The last 6 inches are the rectum and the anal canal. The anal canal ends at the anus (the opening of the large intestine to the outside of the body).

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Anatomy of the lower digestive system, showing the colon and other organs.

Cancer that begins in the colon is called colon cancer, and cancer that begins in the rectum is called rectal cancer. Cancer that begins in either of these organs may also be called colorectal cancer.

Colorectal cancer is the second leading cause of death from cancer in the United States.

In recent years (1995-1999), the number of people diagnosed with colorectal cancer has stayed about the same, but the number of people who die from colorectal cancer has decreased. Colorectal cancer is found more often in men than in women.

Studies show that screening for colorectal cancer decreases the number of deaths from this disease.

Age and health history can affect the risk of developing colon cancer.

Anything that increases a person's chance of getting a disease is called a risk factor. Risk factors for colorectal cancer include the following:

• Being older than 50 years of age.
• Having a personal history of any of the following:
  • Colorectal cancer.
  • Polyps in the colon or rectum.

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    Polyps in the colon. Some polyps have a stalk and others do not. Inset shows a photo of a polyp with a stalk.

  • Cancer of the ovary, endometrium, or breast.
  • Ulcerative colitis or Crohn disease.
• Having a parent, brother, sister, or child with colorectal cancer or polyps.
• Having certain hereditary conditions, such as familial adenomatous polyposis (FAP) and hereditary nonpolyposis colon cancer (HNPCC; Lynch Syndrome).

Refer to the PDQ summary on Genetics of Colorectal Cancer ⁴ for more information about family history and colorectal cancer screening.

Colorectal Cancer Screening

Key Points for This Section

Tests are used to screen for different types of cancer. Five tests are commonly used to screen for colorectal cancer: Fecal occult blood test Sigmoidoscopy Barium enema Colonoscopy Digital rectal exam New screening tests are being studied in clinical trials. Virtual colonoscopy DNA stool test

Tests are used to screen for different types of cancer.

Some screening tests are used because they have been shown to be helpful both in finding cancers early and decreasing the chance of dying from these cancers. Other tests are used because they have been shown to find cancer in some people; however, it has not been proven in clinical trials that use of these tests will decrease the risk of dying from cancer.

Scientists study screening tests to find those with the fewest risks and most benefits. Cancer screening trials also are meant to show whether early detection (finding cancer before it causes symptoms) decreases a person's chance of dying from the disease. For some types of cancer, finding and treating the disease at an early stage may result in a better chance of recovery.

Clinical trials that study cancer screening methods are taking place in many parts of the country. Information about ongoing clinical trials is available from the NCI Web site ⁵.

Five tests are commonly used to screen for colorectal cancer:

Fecal occult blood test

A fecal occult blood test is a test to check stool (solid waste) for blood that can only be seen with a microscope. Small samples of stool are placed on special cards and returned to the doctor or laboratory for testing. Blood in the stool may be a sign of polyps or cancer.

Fecal Occult Blood Test (FOBT) kit to check for blood in stool.

Sigmoidoscopy

Sigmoidoscopy is a procedure to look inside the rectum and sigmoid (lower) colon for polyps, abnormal areas, or cancer. A sigmoidoscope is inserted through the rectum into the sigmoid colon. A sigmoidoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove polyps or tissue samples, which are checked under a microscope for signs of cancer. A sigmoidoscopy and a digital rectal exam (DRE) may be used together to screen for colorectal cancer.

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Sigmoidoscopy. A thin, lighted tube is inserted through the anus and rectum and into the lower part of the colon to look for abnormal areas.

Barium enema

A barium enema is a series of x-rays of the lower gastrointestinal tract. A liquid that contains barium (a silver-white metallic compound) is put into the rectum. The barium coats the lower gastrointestinal tract and x-rays are taken. This procedure is also called a lower GI series.

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Barium enema procedure. The patient lies on an x-ray table. Barium liquid is put into the rectum and flows through the colon. X-rays are taken to look for abnormal areas.

Colonoscopy

Colonoscopy is a procedure to look inside the rectum and colon for polyps, abnormal areas, or cancer. A colonoscope is inserted through the rectum into the colon. A colonoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove polyps or tissue samples, which are checked under a microscope for signs of cancer.

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Colonoscopy. A thin, lighted tube is inserted through the anus and rectum and into the colon to look for abnormal areas.

Digital rectal exam

A digital rectal exam (DRE) is an exam of the rectum. The doctor or nurse inserts a lubricated, gloved finger into the lower part of the rectum to feel for lumps or anything else that seems unusual.

New screening tests are being studied in clinical trials.

Virtual colonoscopy

Virtual colonoscopy is a procedure that uses a series of x-rays called computed tomography to make a series of pictures of the colon. A computer puts the pictures together to create detailed images that may show polyps and anything else that seems unusual on the inside surface of the colon. This test is also called colonography or CT colonography. Clinical trials are comparing virtual colonoscopy with commonly used colorectal cancer screening tests. Other clinical trials are testing whether drinking a contrast material that coats the stool, instead of using laxatives to clear the colon, shows polyps clearly.

DNA stool test

This test checks DNA in stool cells for genetic changes that may be a sign of colorectal cancer.

Screening clinical trials are taking place in many parts of the country. Information about ongoing clinical trials is available from the NCI Web site ⁵.

Risks of Colorectal Cancer Screening

Key Points for This Section

Screening tests have risks. The risks of colorectal cancer screening tests include the following: Damage to the colon can occur. False-negative test results can occur. False-positive test results can occur.

Screening tests have risks.

Decisions about screening tests can be difficult. Not all screening tests are helpful and most have risks. Before having any screening test, you may want to discuss the test with your doctor. It is important to know the risks of the test and whether it has been proven to reduce the risk of dying from cancer.

The risks of colorectal cancer screening tests include the following:

Damage to the colon can occur.

Infection or tears in the lining of the colon can result from sigmoidoscopy, colonoscopy, or the removal of polyps found by screening.

False-negative test results can occur.

Screening test results may appear to be normal even though colorectal cancer is present. A person who receives a false-negative test result (one that shows there is no cancer when there really is) may delay seeking medical care even if there are symptoms.

False-positive test results can occur.

Screening test results may appear to be abnormal even though no cancer is present. A false-positive test result (one that shows there is cancer when there really isn't) can cause anxiety and is usually followed by more tests (such as biopsy), which also have risks.

Your doctor can advise you about your risk for colorectal cancer and your need for screening tests.

Get More Information From NCI

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The NCI has booklets and other materials for patients, health professionals, and the public. These publications discuss types of cancer, methods of cancer treatment, coping with cancer, and clinical trials. Some publications provide information on tests for cancer, cancer causes and prevention, cancer statistics, and NCI research activities. NCI materials on these and other topics may be ordered online or printed directly from the NCI Publications Locator ⁸. These materials can also be ordered by telephone from the Cancer Information Service toll-free at 1-800-4-CANCER (1-800-422-6237), TTY at 1-800-332-8615.

Changes to This Summary (07/12/2007)

The PDQ cancer information summaries are reviewed regularly and updated as new information becomes available. This section describes the latest changes made to this summary as of the date above.

Editorial changes were made to this summary.

Questions or Comments About This Summary

If you have questions or comments about this summary, please send them to Cancer.gov through the Web site’s Contact Form ⁹. We can respond only to email messages written in English.

About PDQ

PDQ is a comprehensive cancer database available on NCI's Web site.

PDQ is the National Cancer Institute's (NCI's) comprehensive cancer information database. Most of the information contained in PDQ is available online at NCI's Web site ⁷. PDQ is provided as a service of the NCI. The NCI is part of the National Institutes of Health, the federal government's focal point for biomedical research.

PDQ contains cancer information summaries.

The PDQ database contains summaries of the latest published information on cancer prevention, detection, genetics, treatment, supportive care, and complementary and alternative medicine. Most summaries are available in two versions. The health professional versions provide detailed information written in technical language. The patient versions are written in easy-to-understand, nontechnical language. Both versions provide current and accurate cancer information.

The PDQ cancer information summaries are developed by cancer experts and reviewed regularly.

Editorial Boards made up of experts in oncology and related specialties are responsible for writing and maintaining the cancer information summaries. The summaries are reviewed regularly and changes are made as new information becomes available. The date on each summary ("Date Last Modified") indicates the time of the most recent change.

PDQ also contains information on clinical trials.

A clinical trial is a study to answer a scientific question, such as whether a method of finding cancer earlier can help people to live longer. Trials are based on past studies and what has been learned in the laboratory. Each trial answers certain scientific questions in order to find new and better ways to help cancer patients and those who are at risk for cancer. During screening clinical trials, information is collected about the effects of a new screening method and how well it works. If a clinical trial shows that a new method is better than one currently being used, the new method may become "standard." People who are at high risk for a certain type of cancer may want to think about taking part in a clinical trial.

Listings of clinical trials are included in PDQ and are available online at NCI's Web site ¹⁰. Descriptions of the trials are available in health professional and patient versions. Many cancer doctors who take part in clinical trials are also listed in PDQ. For more information, call the Cancer Information Service 1-800-4-CANCER (1-800-422-6237); TTY at 1-800-332-8615.

Glossary Terms

Not normal. An abnormal lesion or growth may be cancerous, premalignant (likely to become cancer), or benign.

Having to do with the anus. The anus is the opening of the rectum (last part of the large intestine) to the outside of the body.

The opening of the rectum to the outside of the body.

A procedure in which a liquid with barium in it is put into the rectum and colon by way of the anus. Barium is a silver-white metallic compound that helps to show the image of the lower gastrointestinal tract on an x-ray.

The removal of cells or tissues for examination by a pathologist. The pathologist may study the tissue under a microscope or perform other tests on the cells or tissue. There are many different types of biopsy procedures. The most common types include: (1) incisional biopsy, in which only a sample of tissue is removed; (2) excisional biopsy, in which an entire lump or suspicious area is removed; and (3) needle biopsy, in which a sample of tissue or fluid is removed with a needle. When a wide needle is used, the procedure is called a core biopsy. When a thin needle is used, the procedure is called a fine-needle aspiration biopsy.

A tissue with red blood cells, white blood cells, platelets, and other substances suspended in fluid called plasma. Blood takes oxygen and nutrients to the tissues, and carries away wastes.

The long, tube-shaped organ in the abdomen that completes the process of digestion. The bowel has two parts, the small bowel and the large bowel. Also called the intestine.

A term for diseases in which abnormal cells divide without control. Cancer cells can invade nearby tissues and can spread to other parts of the body through the blood and lymph systems. There are several main types of cancer. Carcinoma is cancer that begins in the skin or in tissues that line or cover internal organs. Sarcoma is cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Leukemia is cancer that starts in blood-forming tissue such as the bone marrow, and causes large numbers of abnormal blood cells to be produced and enter the blood. Lymphoma and multiple myeloma are cancers that begin in the cells of the immune system. Central nervous system cancers are cancers that begin in the tissues of the brain and spinal cord.

A sugar molecule. Carbohydrates can be small and simple (for example, glucose) or they can be large and complex (for example, polysaccharides such as starch, chitin or cellulose).

The individual unit that makes up the tissues of the body. All living things are made up of one or more cells.

A type of research study that tests how well new medical approaches work in people. These studies test new methods of screening, prevention, diagnosis, or treatment of a disease. Also called a clinical study.

The longest part of the large intestine, which is a tube-like organ connected to the small intestine at one end and the anus at the other. The colon removes water and some nutrients and electrolytes from partially digested food. The remaining material, solid waste called stool, moves through the colon to the rectum and leaves the body through the anus.

Cancer that forms in the tissues of the colon (the longest part of the large intestine). Most colon cancers are adenocarcinomas (cancers that begin in cells that make and release mucus and other fluids).

A thin, tube-like instrument used to examine the inside of the colon. A colonoscope has a light and a lens for viewing and may have a tool to remove tissue.

Examination of the inside of the colon using a colonoscope, inserted into the rectum. A colonoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove tissue to be checked under a microscope for signs of disease.

Having to do with the colon or the rectum.

CT scan. A series of detailed pictures of areas inside the body taken from different angles; the pictures are created by a computer linked to an x-ray machine. Also called CT scan, computerized tomography, computerized axial tomography scan, and CAT scan.

A dye or other substance that helps show abnormal areas inside the body. It is given by injection into a vein, by enema, or by mouth. Contrast material may be used with x-rays, CT scans, MRI, or other imaging tests.

Chronic inflammation of the gastrointestinal tract, most commonly the small intestine and colon. Crohn disease increases the risk for colorectal cancer and small intestine cancer. Also called regional enteritis.

The process of identifying a disease, such as cancer, from its signs and symptoms.

A method used to identify a disease.

The organs that take in food and turn it into products that the body can use to stay healthy. Waste products the body cannot use leave the body through bowel movements. The digestive system includes the salivary glands, mouth, esophagus, stomach, liver, pancreas, gallbladder, small and large intestines, and rectum.

DRE. An examination in which a doctor inserts a lubricated, gloved finger into the rectum to feel for abnormalities. Also called DRE.

Deoxyribonucleic acid. The molecules inside cells that carry genetic information and pass it from one generation to the next. Also called deoxyribonucleic acid.

The layer of tissue that lines the uterus.

The muscular tube through which food passes from the throat to the stomach.

A test result that indicates that a person does not have a specific disease or condition when the person actually does have the disease or condition.

A test result that indicates that a person has a specific disease or condition when the person actually does not have the disease or condition.

An inherited condition in which numerous polyps (growths that protrude from mucous membranes) form on the inside walls of the colon and rectum. It increases the risk of colorectal cancer. Also called familial adenomatous polyposis and FAP.

FOBT. A test to check for blood in the stool. Small samples of stool are placed on special cards and sent to a doctor or laboratory for testing. Blood in the stool may be a sign of colorectal cancer. Also called FOBT.

The stomach and intestines. The gastrointestinal tract is part of the digestive system, which also includes the salivary glands, mouth, esophagus, liver, pancreas, gallbladder, and rectum.

Inherited; having to do with information that is passed from parents to offspring through genes in sperm and egg cells.

Transmitted from parent to child by information contained in the genes.

HNPCC. An inherited disorder in which affected individuals have a higher-than-normal chance of developing colorectal cancer and certain other types of cancer, often before the age of 50. Also called HNPCC and Lynch syndrome.

Invasion and multiplication of germs in the body. Infections can occur in any part of the body and can spread throughout the body. The germs may be bacteria, viruses, yeast, or fungi. They can cause a fever and other problems, depending on where the infection occurs. When the body’s natural defense system is strong, it can often fight the germs and prevent infection. Some cancer treatments can weaken the natural defense system.

The long, tube-like organ that is connected to the small intestine at one end and the anus at the other. The large intestine has four parts: cecum, colon, rectum, and anal canal. Partly digested food moves through the cecum into the colon, where water and some nutrients and electrolytes are removed. The remaining material, solid waste called stool, moves through the colon, is stored in the rectum, and leaves the body through the anal canal and anus.

A substance that promotes bowel movements.

A nutrient required to maintain health.

A chemical compound (such as protein, fat, carbohydrate, vitamin, or mineral) contained in foods. These compounds are used by the body to function and grow.

A part of the body that performs a specific function. For example, the heart is an organ.

One of a pair of female reproductive glands in which the ova, or eggs, are formed. The ovaries are located in the pelvis, one on each side of the uterus.

PDQ is an online database developed and maintained by the National Cancer Institute. Designed to make the most current, credible, and accurate cancer information available to health professionals and the public, PDQ contains peer-reviewed summaries on cancer treatment, screening, prevention, genetics, complementary and alternative medicine, and supportive care; a registry of cancer clinical trials from around the world; and directories of physicians, professionals who provide genetics services, and organizations that provide cancer care. Most of this information, and more specific information about PDQ, can be found on the NCI's Web site at http://www.cancer.gov/cancertopics/pdq. Also called Physician Data Query.

A growth that protrudes from a mucous membrane.

In medicine, action taken to decrease the chance of getting a disease or condition. For example, cancer prevention includes avoiding risk factors (such as smoking, obesity, lack of exercise, and radiation exposure) and increasing protective factors (such as getting regular physical activity, staying at a healthy weight, and having a healthy diet).

A molecule made up of amino acids that are needed for the body to function properly. Proteins are the basis of body structures such as skin and hair and of substances such as enzymes, cytokines, and antibodies.

By or having to do with the rectum. The rectum is the last several inches of the large intestine closest to the anus.

The last several inches of the large intestine closest to the anus.

Something that may increase the chance of developing a disease. Some examples of risk factors for cancer include age, a family history of certain cancers, use of tobacco products, certain eating habits, obesity, lack of exercise, exposure to radiation or other cancer-causing agents, and certain genetic changes.

Checking for disease when there are no symptoms. Since screening may find diseases at an early stage, there may be a better chance of curing the disease. Examples of cancer screening tests are the mammogram (breast), colonoscopy (colon), Pap smear (cervix), and PSA blood level and digital rectal exam (prostate). Screening can also include checking for a person’s risk of developing an inherited disease by doing a genetic test.

The S-shaped section of the colon that connects to the rectum.

A thin, tube-like instrument used to examine the inside of the colon. A sigmoidoscope has a light and a lens for viewing and may have a tool to remove tissue.

Examination of the lower colon using a sigmoidoscope, inserted into the rectum. A sigmoidoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove tissue to be checked under a microscope for signs of disease. Also called proctosigmoidoscopy.

The part of the digestive tract that is located between the stomach and the large intestine.

The extent of a cancer in the body. Staging is usually based on the size of the tumor, whether lymph nodes contain cancer, and whether the cancer has spread from the original site to other parts of the body.

An organ that is part of the digestive system. The stomach helps digest food by mixing it with digestive juices and churning it into a thin liquid.

The material in a bowel movement. Stool is made up of food that was not digested, bacteria, mucus, and cells from the intestines. Also called feces.

An indication that a person has a condition or disease. Some examples of symptoms are headache, fever, fatigue, nausea, vomiting, and pain.

The hollow tube inside the neck that starts behind the nose and ends at the top of the trachea (windpipe) and esophagus (the tube that goes to the stomach). The throat is about 5 inches long, depending on body size. Also called the pharynx.

A group or layer of cells that work together to perform a specific function.

Chronic inflammation of the colon that produces ulcers in its lining. This condition is marked by abdominal pain, cramps, and loose discharges of pus, blood, and mucus from the bowel.

A method under study to examine the colon by taking a series of x-rays (called a CT scan) and using a high-powered computer to reconstruct 2-D and 3-D pictures of the interior surfaces of the colon from these x-rays. The pictures can be saved, manipulated to better viewing angles, and reviewed after the procedure, even years later. Also called computed tomography colography.

A key nutrient that the body needs in small amounts to grow and stay strong. Examples are vitamins A, C, and E.

A type of high-energy radiation. In low doses, x-rays are used to diagnose diseases by making pictures of the inside of the body. In high doses, x-rays are used to treat cancer.