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Colorectal cancer is a disease in which cancer cells grow in either the colon or the rectum. The colon and rectum are part of the large intestine, which is located in the abdomen between the small intestine and the anus. The large intestine is part of the body’s digestive system. It removes nutrients from food and stores waste until it passes out of the body. The large intestine, also called large bowel or colon, runs from the small intestine to the anus. The large intestine is divided into several parts, including the ascending, transverse, descending, and sigmoid colon, along with the rectum.
Normally, the cells in the colon and rectum divide in a regulated manner. If cells keep dividing when new cells are not needed, a mass of tissue called a tumor forms. A tumor can be benign or malignant.
A benign tumor is not cancer. It does not spread to other parts of the body. A malignant tumor is cancer. Cancer cells divide and damage tissue around them. They can enter the bloodstream and spread to other parts of the body.
The colon is divided into four sections:
As we eat, bile acids from the liver and gallbladder and powerful digestive enzymes from the pancreas are secreted into the small intestine, where they break down the nutrient portions of food into forms that can be carried by the bloodstream to the liver. Here they are metabolized. What remains after these acids and enzymes do their work—water, minerals, and a watery form of digested food (called chyme)—is transported through the colon to the rectum, where it is stored as feces and eventually expelled.
Colon cancer may occur anywhere in the large intestine, but most colon cancers occur in the upper rectum and adjoining sigmoid colon.
Colon cancer tends to be a slow-growing form of cancer. Before colon cancer develops, there are often changes that occur in the lining of the colon or rectum. One type of change is the development of polyps—growths that project from the lining of the colon or rectum.
Some types of polyps, such as inflammatory polyps, are benign. However, other types—such as adenomatous polyps and hyperplastic polyps—may be precancerous. The risk of polyps turning into cancer is increased if the polyps are flat, large, numerous in quantity, or have a slender, fingerlike structure, as opposed to a tubular structure.
Polyps are painless. A sign that may indicate the presence of polyps is rectal bleeding. If you notice blood in the stool or rectal bleeding, you should contact your doctor to have a colonoscopy, a test that will check for the presence of polyps. If polyps are found, your doctor will remove the polyps (polypectomy) and have them analyzed at a lab to determine if they are cancerous. (See “ Screening for Colon Cancer ” for more detailed information on these tests.) Removing polyps before they become malignant is an effective way to reduce your risk of developing colon cancer.
Most types (nearly 95%) of colon cancers are adenocarcinomas, cancers of the cells that line the interior of the colon and rectum. Adenocarcinomas are derived from the glandular components of the lining of the bowel. Other types of colon cancer, which are more rare, include:
Some colon cancers are caused by genetics and run in families. The two most common forms of inherited colon cancer are:
Colon cancer is the second leading cause of cancer-related death in men and women in the United States, with an estimated 56,600 deaths occurring in 2002. Approximately 148,300 people will be diagnosed with colon or rectal cancer this year; 107,300 will have colon cancer and 41,000 people will develop rectal cancer.
Colorectal cancer is one of the more treatable forms of cancer, and the rate of successful treatment is quite high, especially when the cancer is treated early.
The exact cause of colon cancer is not known. Since colon cancer is more prevalent in industrialized countries, there has been speculation that colon cancer may be associated with diets that are high in fat and calories and low in fiber. However, studies have yielded conflicting results, and further research is necessary. Genetics are also believed to play a role.
Sources:
National Cancer Institute
http://www.nci.nih.gov/
American Gastroenterological Association
http://www.gastro.org/
American Cancer Society
http://www.acs.org
Colorectal Cancer: Mayo Foundation for Medical Education and Research
http://www.mayoclinic.com/invoke.cfm?id=DS00035
Last reviewed February 2003 by Jondavid Pollock, MD, PhD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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