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 Other 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 Cancer.gov Web site ¹.

Five tests are commonly used to screen for colorectal cancer:

Fecal occult blood test

A fecal occult blood test (FOBT) checks 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.

Sigmoidoscopy

Sigmoidoscopy is a procedure to look inside the rectum and sigmoid (lower) colon for polyps, abnormal areas, or cancer. A sigmoidoscope (a thin, lighted tube) is inserted through the rectum into the sigmoid colon. Polyps or tissue samples may be taken for biopsy. A sigmoidoscopy and a digital rectal exam (DRE) may be used together to screen for colorectal cancer.

Barium enema

A barium enema (BE) 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.

Colonoscopy

Colonoscopy is a procedure to look inside the rectum and colon for polyps, abnormal areas, or cancer. A colonoscope (a thin, lighted tube) is inserted through the rectum into the colon. Polyps or tissue samples may be taken for biopsy.

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.

Other 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.

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 Cancer.gov Web site ¹.

Glossary Terms

Not normal. In referring to a lesion or growth, may be cancerous or premalignant (likely to become cancer).

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 under a microscope. When only a sample of tissue is removed, the procedure is called an incisional biopsy or core biopsy. When an entire lump or suspicious area is removed, the procedure is called an excisional biopsy. When a sample of tissue or fluid is removed with a needle, the procedure is called a needle biopsy or fine-needle aspiration.

A term for diseases in which abnormal cells divide without control. Cancer cells can invade nearby tissues and can spread through the bloodstream and lymphatic system to other parts of the body. 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 bloodstream. Lymphoma is cancer that begins in the cells of the immune system.

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

A type of research study that uses volunteers to test new methods of screening, prevention, diagnosis, or treatment of a disease. The trial may be carried out in a clinic or other medical facility. 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.

A thin, lighted tube used to examine the inside of the colon.

An examination of the inside of the colon using a thin, lighted tube (called a colonoscope) inserted into the rectum. If abnormal areas are seen, tissue can be removed and examined under a microscope to determine whether disease is present.

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 computerized tomography and computerized axial tomography (CAT) scan.

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

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

FOBT. A test to check for blood in stool. (Fecal refers to stool; occult means hidden.)

The stomach and intestines.

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

A growth that protrudes from a mucous membrane.

The last several inches of the large intestine. The rectum ends at the anus.

Checking for disease when there are no symptoms.

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

A thin, lighted tube used to view the inside of the colon.

Inspection of the lower colon using a thin, lighted tube called a sigmoidoscope. Samples of tissue or cells may be collected for examination under a microscope. Also called proctosigmoidoscopy.

The extent of a cancer within the body. If the cancer has spread, the stage describes how far it has spread from the original site to other parts of the body.

The waste matter discharged in a bowel movement; feces.

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

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

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 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.