Colon Cancer: Screening and Early Detection

by Food and Drug Administration (FDA)

Imagine taking a fantastic voyage through the highways and byways of the human body. With a touch of a finger on the controls of your vehicle, you "fly" down strangely scenic routes and dark tunnels. Along the way, you note dangers and relay them back to technicians for future repair. Sound farfetched? Not really.

By using new computer-assisted technology, doctors can visualize a person's colon just as if they were there. Called "virtual colonoscopy," this screening test projects a three-dimensional image of the colon onto a computer screen. The physician "flies" through its length, searching for lumps that might be cancerous. The test is non-invasive and often involves much less discomfort than conventional methods of examining the colon. Sedation is seldom required, and the patient can go home immediately after the procedure.

"Virtual colonoscopy has the potential to revolutionize how we screen for colon cancer," says Brian E. Harvey, M.D., a senior medical officer in the Food and Drug Administration's Center for Devices and Radiological Health. "It's very exciting, and once all the data are in, we may find we can screen the entire population over the age of 50, which can lead to early detection of more colonic polyps and colorectal cancer."

When this technique is perfected, it will be added to the arsenal of tools used for the prevention and early diagnosis of colorectal cancer. Although this cancer remains a very scary disease, such new detection technologies improve the chance of finding the tumor early in its growth when it's most curable. In addition, therapeutic advances offer new hope that, even if the cancer has spread, the diagnosis of colon cancer will not be fatal. A Killer Disease and Its Risk Factors

Colorectal cancer — cancer of the large intestine and rectum — is second only to lung cancer in the number of cancer deaths it causes. The American Cancer Society estimates that more than 130,000 Americans will be diagnosed with colorectal cancer in 2000, and more than 56,000 will die from the disease this year. On average, one in 20 people will develop the disease in the course of a lifetime. Ninety percent of cases occur in patients over age 50, and the majority of cases — 75 percent — occur in people with no known medical risk factors for colorectal cancer. But certain factors can sharply increase risk. They include:

Family history. Having a first-degree relative — mother or father, for example — with colorectal cancer increases the lifetime risk of developing the disease to as high as eight-fold greater than people without a family history.

History of bowel disease. Risk increases 30-fold in patients with a history of inflammatory bowel disorders, such as Crohn's disease or ulcerative colitis.

History of adenomatous polyps. Most colorectal cancers begin as small precancerous growths, called polyps, inside the colon or rectum. Villous adenomatous polyps are the most likely to become cancerous (up to 25 percent). Tubular adenomatous polyps are estimated to become malignant 1 to 5 percent of the time.

Genetic traits. A genetic syndrome known as Familial Cancer Syndrome or Hereditary Non-Polyposis Colon Cancer markedly increases the risk for developing colorectal cancer at an earlier age than those patients at average risk.

Signs and Symptoms

The colon and rectum make up the large intestine, the end of the long tube of the gastrointestinal tract through which food passes during digestion. (This interconnected gastrointestinal organ system also includes the esophagus, stomach and small intestine.) The colon is the upper five or six feet of the large intestine, and the rectum is the last six to eight inches. Cancer begins to develop when cells in the colon multiply uncontrollably. These cell mutations result in precancerous polyps, small protrusions from the intestine's lining.

There are several types of polyps, and they become increasingly common with age. By age 50, 10 percent of the population has polyps, but by age 65 that number grows to 30 percent. If left untreated, 8 to 12 percent of polyps will become cancerous. If allowed to grow, the tumor can invade nearby organs. Once the disease enters the lymph nodes or bloodstream, it most often spreads to the liver.

As with many cancers, there are usually no symptoms in the early stages. Polyps do sometimes bleed, and there may be some noticeable rectal bleeding. However, most of the time, this blood is invisible to the naked eye and is only detectable microscopically.

Patient symptoms begin to appear once the tumor is large enough to cause obstruction of the bowel. They include:

• anemia
• rectal bleeding with bright, red blood
• blood in the stool, characterized by black, "tarry" stools
• a change in bowel habits, such as recurrent diarrhea or worsening constipation
• persistent abdominal pain
• generalized weakness or fatigue
• unexplained weight loss

About the Author

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FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.