Frequently Asked Questions

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Frequently Asked Questions

Digestive-Tract Cancer
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Frequently Asked Questions
Frequently Asked Questions
Answers to common questions about colorectal cancer prevention and screening.
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Reviewed by the Faculty of Harvard Medical School

Frequently Asked Questions About Colorectal Cancer

What Is Colorectal Cancer?

Like all cancers, colorectal cancer occurs when cells grow out of control. The cancer cells form a tumor, which invades and destroys nearby tissue. The cells also can break off and move to other parts of the body, where they can start a new tumor.

Colorectal cancer occurs in the lower intestine, which includes the colon and rectum. The colon, a 5- to 6-foot-long muscular tube, is the final part of the intestinal tract that ends in the rectum. The rectum comprises the intestinal tract's final few inches.

How Common Is Colorectal Cancer?

According to the American Cancer Society, not counting skin cancers, colorectal cancer is the third most common cancer found in men and women in this country. Overall, the lifetime risk of developing colorectal cancer is about 1 in 20. The American Cancer Society 2011 estimates for colorectal cancer in the United States are about:
  • 97,000 new cases of colon cancer
  • About 40,000 new cases of rectal cancer
  • About 50,000 deaths from colorectal cancer

Who Gets Colorectal Cancer?

Anyone can get the disease. Men and women are equally susceptible. Chances of developing colorectal cancer increase with age; the disease is more common after age 50. Among ethnic groups in the United States, African-Americans have the highest incidence and highest rate of death from colorectal cancer.

Who is at greatest risk? Individuals with personal or family history of colorectal cancer or with chronic inflammatory bowel disease (Crohn's disease or ulcerative colitis).

Can Colorectal Cancer Be Prevented?

Currently, no sure-fire method exists for preventing colorectal cancer. This makes early detection by having a screening test extremely important, especially if you're over age 50.

How Does It Start?

Colorectal cancer is thought to develop slowly over several years. Almost all colorectal cancers begin as a small growth or polyp, also known as an adenoma.

What Is A Polyp?

A polyp is a growth of tissue that erupts from the lining of the large intestine. A small number of polyps will grow into cancer; most won't. The larger the polyp, the greater the chance it contains cancerous cells. To prevent cancer, your doctor will remove polyps during screening.

What Causes Colorectal Cancer?

Researchers don't know the exact cause of colorectal cancer. However, scientists have been able to identify factors that increase your chance of getting the disease. These risk factors include:

  • Aging. Chances of developing colorectal cancer increase after age 50. The American Cancer Society notes that about 90 percent of people diagnosed with colorectal cancer are older than age 50.
  • Smoking. Studies show that smokers are up to 40 percent more likely than nonsmokers to die of colorectal cancer.
  • Family history. Your risk of developing colorectal cancer is higher than average if you have a parent or sibling who developed the disease before age 60. Some families share genes that make members much more susceptible to the disease; the rate of colorectal cancer in these families is very high.
  • Personal history. Your risk of getting colorectal cancer increases if you have had intestinal polyps (though not all types of polyps increase the risk) or chronic inflammatory bowel disease. Some women with a history of cancer of the ovary, uterus or breast may have a somewhat greater chance of developing colorectal cancer. 
  • Obesity. Excess fat, especially in the waist area, increases your risk.
  • Physical inactivity. People who exercise regularly and generally engage in more physical activity during the day appear to have a lower risk of colorectal cancer. 
  • Diet. Eating more fruits, vegetables and whole grains may reduce your risk.

What Are The Symptoms Of Colorectal Cancer?

Unfortunately, the early stages of the disease, when it's most curable, usually don't produce any symptoms. By the time symptoms show up, the cancer may be far advanced. Still, you should watch for the following: a marked change in bowel habits, rectal bleeding, marked thinning of the stools, and unexplained weight loss.


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Last updated September 10, 2014

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