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Cancer begins when normal cells begin to change and grow uncontrollably, forming a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body).
Colorectal cancer is a disease in which normal cells in the lining of the colon or rectum begin to change, start to grow uncontrollably, and no longer die. These changes usually take years to develop; however, in some cases of hereditary disease, changes can occur within months to years. Both genetic and environmental factors can cause the changes. Initially, the cell growth appears as a benign polyp that can, over time, become a cancerous tumor. If not treated or removed, a polyp can become a potentially life-threatening cancer. Recognizing and removing precancerous polyps before they become cancer can prevent colorectal cancer.
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Anatomy of the colon and rectum
The colon and rectum make up the large intestine, which plays an important role in the body's ability to process waste. The colon makes up the first five to six feet of the large intestine, and the rectum makes up the last six inches, ending at the anus.
The colon has four sections. The ascending colon is the portion of the colon that extends from a pouch called the cecum (the start of the large intestine into which the small intestine empties) on the right side of the abdomen. The transverse colon crosses the top of the abdomen. The descending colon takes waste down the left side. Finally, the sigmoid colon at the bottom takes waste a few more inches downward to the rectum.
Colorectal cancer can begin in either the colon or the rectum. Cancer that begins in the colon is called colon cancer, and cancer that begins in the rectum is called rectal cancer.
Colorectal cancer often begins in polyps, noncancerous growths that may develop on the inner wall of the colon and rectum, as people get older. There are several forms of polyps. Adenomatous polyps, or adenomas, are growths that may become cancerous and can be detected with a colonoscopy (see Risk Factors and Prevention). One way to prevent colorectal cancer is to detect and remove polyps before they become cancerous. About 10% of colon polyps are flat and hard to detect through colonoscopy, unless a dye is used to highlight them. These flat polyps have a high risk of becoming cancerous, regardless of their size.
Most colon and rectal cancers are a type of tumor called adenocarcinoma, which is cancer of the cells that line the inside tissue of the colon and rectum. This section covers specifically adenocarcinoma. Other types of cancer that occur far less frequently but can begin in the colon or rectum include carcinoid tumor, gastrointestinal stromal tumor (GIST), and lymphoma.
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When colorectal cancer is detected early, it can often be cured. The death rate from this type of cancer has been declining for the past 20 years, possibly because more cases are now detected early and treatments have improved. Colorectal cancer is the third most common cancer among both men and women in the United States. It is also the third most common cause of cancer death among men and women separately (and the second most common cause of cancer death total if men and women are combined) in the United States.
In 2009, an estimated 146,970 adults (75,590 men and 71,380 women) in the United States will be diagnosed with colorectal cancer. These numbers include 106,100 new cases of colon cancer and 40,870 new cases of rectal cancer. It is estimated that 49,920 deaths (25,240 men and 24,680 women) will occur.
If the cancer is detected at an early, localized stage, the five-year relative survival rate (the percentage of people who survive at least five years after the cancer is detected, excluding those who die from other diseases) for people with colorectal cancer is 90%. If the cancer has spread to adjacent lymph nodes or organs, the five-year relative survival rate is 68%. If the cancer has spread to distant parts of the body, the five-year relative survival rate is 11%. However, for patients who have just one or a few tumors that have spread from the colon to the lung or liver, surgical removal can lead to cure, which greatly improves the five-year survival rate for these patients.
Cancer survival statistics should be interpreted with caution. These estimates are based on data from thousands of cases of this type of cancer in the United States each year, but the actual risk for a particular individual may differ. It is not possible to tell a single individual how long he or she will live with colorectal cancer. Because the survival statistics are measured in five-year intervals, they may not represent advances made in the treatment or diagnosis of this cancer.
Statistics adapted from the American Cancer Society's publication, Cancer Facts & Figures 2009.
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