Colorectal Cancer

August 8, 2011

The lifetime risk of developing colon cancer is about 60% and is slightly higher in men than in women. Half of those affected persons will die of the disease. It is rare before the age of 50 years and the incidence increases thereafter. Death caused by colon cancer has decreased over the last 20 years. Colorectal cancer death rates are rising in African Americans. The overall 5-year survival rate for colorectal cancer is 60%.

Digestive system anatomy

The digestive system consists of the esophagus, stomach, small bowel, colon, and rectum. The colon and the rectum store the waste until it is evacuated from the body. The colon and the rectum form a long muscular tube about 6 ft long also known as the large intestine. The rectum is the specific name for the last 8-10 in. of the colon.

Risk factors for colorectal cancer

Multiple factors can increase the risk for colon cancer. Being born in North America or Western Europe is a risk factor. A diet that is high in fat, red meat, and sucrose may contribute to colorectal cancer. Alcohol consumption, smoking, obesity, and a history of pelvic radiation are also risk factors. Colorectal cancer occurs as people age and those with a longstanding history of ulcerative colitis are at high risk. Persons with firstdegree relatives, that is, parents and siblings with colorectal cancer, are at increased risk to develop it. In general, it is recommended that the latter group start to have colorectal cancer screening 10 years before the age that the relative was diagnosed. On the other hand, those born in Africa or Asia are at lesser risk for colorectal cancer. Diets that are rich in fruits, vegetables, and fiber, along with high intake of calcium appear to decrease the risk for colorectal cancer. There is a suggestion that postmenopausal hormone replacement in women, long-term aspirin, or nonsteroidal antiinflammatories and vigorous activity are also protective against colorectal cancer.

How does cancer develop?

It is felt that colorectal cancers arise from polyps, specifically adenomatous polyps. Of Americans over the age of 50, 30-50% will develop these polyps. One in 20 adenomas will progress to cancer and this occurs over a period of over 10 years. The cancer risk is related to specifics of the adenomas including their size, number, architecture, and abnormalities seen at the cellular level on microscopic examination. It is based on this understanding that screening for colorectal cancer is done.

Definitions

1. A fecal occult blood test (FOBT) is a test used to look for small amounts of blood in the stool that cannot be seen with the naked eye.
3. A sigmoidoscopy is an examination of the rectum and the lower colon, using a lighted instrument called a sigmoidoscope. These scopes are usually 60-70 cm (24-28 in.) in length.
5. A colonoscopy is an examination of the rectum and the entire colon, using a lighted instrument.
7. A double contrast barium enema (DCBE) is a series of x-rays of the colon and rectum. The patient receives an enema with barium, which outlines the colon and rectum. This also defines masses and other abnormalities of the lining of the colon.

SEE ALSO: Cancer, Pain, Preventive care

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Category: C, Colorectal Cancer