Colon Cancer

What is colon cancer?

Colon cancer is a disease in which abnormal cells in the colon or rectum divide uncontrollably, ultimately forming a malignant tumor. Most colon cancers begin as a polyp, a growth in the tissue that lines the inner surface of the colon or rectum. Polyps may be flat, or they may be raised. Raised polyps may grow on the inner surface of the colon or rectum like mushrooms without a stalk (sessile polyps), or they may grow like a mushroom with a stalk (pedunculated polyps). Polyps are common in people older than 50 years of age, and most are not cancer. However, a certain type of polyp known as an adenoma may have a higher risk of becoming a cancer.

What are the causes and risks of colon cancer?

The major risk factors for colon cancer are a family history of the disease and older age, but several other factors have been associated with increased risk, including:

• Excessive alcohol use.
• Obesity.
• Being physically inactive.
• Cigarette smoking.
• Poor diet.

In addition, people with a history of inflammatory bowel disease (such as ulcerative colitis or Crohn’s disease) have a higher risk of colorectal cancer than people without such conditions. And people who have certain inherited conditions (such as Lynch syndrome and familial adenomatous polyposis) also have an increased risk of colorectal cancer.

What are the signs and symptoms of colon cancer?

Many of the symptoms of colon cancer can also be caused by something that isn’t cancer, such as an infection, hemorrhoids, irritable bowel syndrome or inflammatory bowel disease.

In most cases, people who have these symptoms do not have cancer. Still, if you have any of these symptoms you should talk to your provider:

• A change in bowel habits, such as diarrhea, constipation, or narrowing of the stool, that lasts for more than a few days.
• A feeling that you need to have a bowel movement that is not relieved by doing so.
• Rectal bleeding.
• Dark stools, or blood in the stool.
• Cramping or abdominal (belly) pain.
• Weakness and fatigue.
• Unintended weight loss.

What do I need to know about colon cancer screening?

Expert medical groups, including the U.S. Preventive Services Task Force (USPSTF), strongly recommend screening for colon cancer. Although minor details of the recommendations may vary, these groups generally recommend that people at average risk of colon cancer get screened at regular intervals beginning at age 50 years.

The USPSTF recommends that screening continue to age 75 years; after age 75, the decision to screen is based on patient’s life expectancy, health status, comorbid conditions, and prior screening results. Routine screening of people aged 86 years or older is not recommended by the USPSTF.

People at increased risk because of a family history of colorectal cancer or polyps or because they have inflammatory bowel disease or certain inherited conditions may be advised to start screening before age 50 and/or have more frequent screening.

The USPSTF considers the following methods to be acceptable screening tests for colorectal cancer:

• High-sensitivity fecal occult blood tests (FOBT). Both polyps and colorectal cancers can bleed, and FOBT checks for tiny amounts of blood in feces (stool) that cannot be seen visually. (Blood in stool may also indicate the presence of conditions that are not cancer, such as hemorrhoids.) Currently, two types of FOBT are approved by the Food and Drug Administration (FDA) to screen for colorectal cancer: guaiac FOBT (gFOBT) and the fecal immunochemical (or immunohistochemical) test (FIT, also known as iFOBT). With both types of FOBT, stool samples are collected by the patient using a kit, and the samples are returned to the doctor.
  • Guaiac FOBT uses a chemical to detect heme, a component of the blood protein hemoglobin. Because the guaiac FOBT can also detect heme in some foods (for example, red meat), people have to avoid certain foods before having this test.
  • FIT uses antibodies to detect human hemoglobin protein specifically. Dietary restrictions are typically not required for FIT.

  Studies have shown that guaiac FOBT, when performed every one to two years in people aged 50 to 80 years, can help reduce the number of deaths due to colorectal cancer by 15 to 33 percent. If FOBT is the only type of colorectal cancer screening test performed, experts generally recommend yearly testing.

• Stool DNA test (FIT-DNA). The only stool DNA test approved by the FDA to date, Cologuard®, is a multitarget test that detects tiny amounts of blood in stool (with an immunochemical test similar to FIT) as well as nine DNA biomarkers in three genes that have been found in colorectal cancer and precancerous advanced adenomas. The DNA comes from cells in the lining of the colon and rectum that are shed and collect in stool as it passes through the large intestine and rectum. As with both types of FOBT, the stool sample for the FIT-DNA test is collected by the patient using a kit; the sample is mailed to a laboratory for testing. A computer program analyzes the results of the two tests (blood and DNA biomarkers) and provides a finding of negative or positive. People who have a positive finding with this test are advised to have a colonoscopy. In one study of people who were at average risk of developing colon cancer and had no symptoms of colon problems, this test detected more cancers and adenomas than the FIT test (that is, it was more sensitive). However, the FIT-DNA test also was more likely to identify an abnormality when none was actually present (that is, it had more false-positive results).

• Sigmoidoscopy. In this test, the rectum and sigmoid colon are examined using a sigmoidoscope, a flexible lighted tube with a lens for viewing and a tool for removing tissue. This instrument is inserted through the anus into the rectum and sigmoid colon as air (or carbon dioxide) is pumped into the colon to expand it so the doctor can see the colon lining more clearly. During sigmoidoscopy, abnormal growths in the rectum and sigmoid colon can be removed for analysis (biopsied). The lower colon must be cleared of stool before sigmoidoscopy, but the preparation is less extensive than that required for colonoscopy. People are usually not sedated for this test. Studies have shown that people who have regular screening with sigmoidoscopy after age 50 years have a 60 to 70 percent lower risk of death due to cancer of the rectum and lower colon than people who do not have screening. One randomized controlled clinical trial found that even just one sigmoidoscopy screening between 55 and 64 years of age can substantially reduce colorectal cancer incidence and mortality. Experts generally recommend sigmoidoscopy every five years with or without gFOBT or FIT every three years for people at average risk who have had negative test results.

• Standard (or optical) colonoscopy. In this test, the rectum and entire colon are examined using a colonoscope, a flexible lighted tube with a lens for viewing and a tool for removing tissue. Like the shorter sigmoidoscope, the colonoscope is inserted through the anus into the rectum and the colon as air (or carbon dioxide) is pumped into the colon to expand it so the doctor can see the colon lining more clearly. During colonoscopy, any abnormal growths in the colon and the rectum can be removed, including growths in the upper parts of the colon that are not reached by sigmoidoscopy. A thorough cleansing of the entire colon is necessary before this test. Most patients receive some form of sedation during the test. Studies suggest that colonoscopy reduces deaths from colorectal cancer by about 60 to 70 percent. Additional studies are currently being done to better evaluate how effective colonoscopy screening methods are. Experts recommend colonoscopy every 10 years for people at average risk as long as their test results are negative.

• Virtual colonoscopy. This screening method, also called computed tomographic (CT) colonography, uses special X-ray equipment (a CT scanner) to produce a series of pictures of the colon and the rectum from outside the body. A computer then assembles these pictures into detailed images that can show polyps and other abnormalities. Virtual colonoscopy is less invasive than standard colonoscopy and does not require sedation. As with standard colonoscopy, a thorough cleansing of the colon is necessary before this test, and air (or carbon dioxide) is pumped into the colon to expand it for better viewing of the colon’s lining. The accuracy of virtual colonoscopy is similar to that of standard colonoscopy, and virtual colonoscopy has a lower risk of complications. However, if polyps or other abnormal growths are found during a virtual colonoscopy, a standard colonoscopy is usually performed to remove them.Whether virtual colonoscopy can help reduce deaths from colorectal cancer is not yet known, and Medicare and some insurance companies currently do not pay for the costs of this procedure. Studies are ongoing to compare virtual colonoscopy with other screening methods.

When should I should I begin colon cancer screening?

People should talk with their health care provider about when to begin screening for colon cancer, what test(s) to have, the advantages and disadvantages of each test, how often to undergo screening, and when to stop.

The decision about which test to have usually takes into account several factors, including:

• Your age, medical history, family history, and general health.
• The potential risks of the test.
• The preparation required for the test.
• Whether sedation may be needed for the test.
• The follow-up care needed after the test.
• The convenience of the test.
• The cost of the test and the availability of insurance coverage.

What are the advantages and disadvantages of colon cancer screening?

Colorectal cancer screening tests all have advantages and disadvantages. You should talk through the screening options with your healthcare provider:

Fecal Occult Blood Test (guaiac FOBT or fecal immunochemical test [FIT])

Advantages:

• No cleansing of the colon is necessary.
• No dietary restrictions are needed before FIT.
• Samples can be collected at home.
• Cost is low compared with other colorectal cancer screening tests.
• There is no risk of damage to the lining of the colon.
• No sedation is needed.

Disadvantages:

• The test does not detect some polyps and cancers.
• False-positive test results are possible (that is, the test may suggest an abnormality when none is present).
• Dietary restrictions are needed before guaiac FOBT.
• Additional procedures, such as colonoscopy, may be needed if the test result shows blood in the stool.

Stool DNA Test (FIT-DNA)

Advantages:

• No cleansing of the colon is necessary.
• No dietary restrictions are needed before the test.
• Samples can be collected at home.
• There is no risk of damage to the lining of the colon.
• No sedation is needed.

Disadvantages:

• Cost may be higher than that of gFOBT or FIT.
• Test sensitivity for adenomas is low.
• False-positive test results are possible (that is, the test may suggest an abnormality when none is present).
• Additional procedures, such as colonoscopy, may be needed if the test result is positive for blood or abnormal DNA.

Sigmoidoscopy

Advantages:

• For most patients, discomfort is minimal, and complications are rare.
• The doctor can perform a biopsy or polypectomy (removal of a polyp or adenoma) during the test, if necessary.
• Less extensive cleansing of the colon is necessary for this test than for a colonoscopy.
  Sedation is often not required.

Disadvantages:

• Abnormal growths in the upper part of the colon will be missed because the test allows the doctor to view only the rectum and the lower part of the colon.
• Bowel cleansing is needed before the test.
• Medication and diet changes may be needed before the test.
• There is a very small risk of bleeding or of tearing or perforation of the lining of the colon.
• Additional procedures, such as colonoscopy, may be needed if the test finds an abnormality.
• The availability of sigmoidoscopy has decreased substantially in the United States in recent years.

Standard Colonoscopy

Advantages:

• This test is one of the most sensitive currently available.
• It allows the doctor to view the rectum and the entire colon.
• The doctor can perform a biopsy or polypectomy during the test if necessary.

Disadvantages:

• Even though this test is highly sensitive, it still may not detect all small polyps, flat or depressed (nonpolypoid) lesions, or cancers.
• A thorough cleansing of the colon is required before the test.
• Diet changes are needed before the test, and medications may need to be adjusted.
• Some form of sedation is almost always used. As a result, the patient must have someone accompany them to the procedure and drive them home afterward, and they may not be able to work the day of the procedure.
• There is a small risk of bleeding or of tearing or perforation of the lining of the colon; this risk increases with age, with the presence of other health problems, and when polyps are removed.

Virtual Colonoscopy

Advantages:

• With this minimally invasive procedure there is little risk of damage to the lining of the colon.
• No sedation is needed.

Disadvantages:

• A thorough cleansing of the colon is required before the test.
• Can miss small polyps.
• Additional procedures, such as colonoscopy, may be needed if the test finds an abnormality.
• Patient is exposed to small amounts of ionizing radiation.
• Not covered by all health insurance plans or Medicare.
• Can unintentionally discover medical results outside the colon that may trigger unnecessary procedures or follow-up.