Colorectal cancer is unchecked cell growth in the large intestine (colon) or rectum that results in tumors that can spread to other parts of the body. Figure 01 The colon and rectum make up the end of the 30-foot-long digestive tract. The colon is the 5 feet of muscular tubing near the end that receives digested nutrients from the small intestine and passes non-absorbed waste on to the rectum (the last 8 to 10 inches of the tract), where they are held before they are expelled through the anus.
Figure 01. Colorectal cancer
Colorectal cancer can arise anywhere in the colon or rectum. The majority of cases (60%) occur in the lower part of the colon or rectum. A quarter of cancers show up in the rectum. Colorectal cancer tends to develop slowly over many years, and starts out as precancerous lesions or polyps. When detected and treated early enough, colorectal cancer is usually curable. Unfortunately, however, most cases are detected after the cancer has spread, which is why colorectal cancer is the second-leading cancer killer in the U.S.
Colorectal cancer occurs when abnormal cells in the lining the colon or rectum proliferate out of control. The cancer may originate on the surface of the intestinal lining or on a bud on a stalk that protrudes from the intestinal wall (polyp). Colorectal polyps are very common. As many as 40% of Americans have them by age 50. Most polyps remain noncancerous (benign), but about 5 to 10% go on to become cancerous (malignant) if they are not removed. As the cancer grows, it begins to invade the intestinal wall. Without treatment, it can infiltrate nearby tissues and lymph nodes and spread through the blood to the liver and other organs.
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