Colon cancer is characterized by malignant tumors on the colon, the rectum, and/or the appendix. It is the third most common form of cancer and a leading cause of death by cancer, second only to lung cancer. In the United States, there is a seven percent chance that any given person will develop cancer of the colon during his or her lifetime. Colon cancer develops from adenomatous, or glandular, polyps in the colon and rectum.
People with a personal or hereditary history of cancer or intestinal polyps are at greater risk for the disease, and the likelihood of developing colon cancer increases with age. In addition, behavioral factors can increase one's risk of cancer of the colon. Smoking cigarettes, heavy drinking, and lack of physical exercise are all risk factors, along with a diet high in red meat and low in fruit, vegetables, fish, and poultry.
Early symptoms of colon cancer are often not very noticeable; they can include blood in the stool, anemia, fatigue, and weight loss. Local symptoms such as changes in bowel habits or, in extreme cases, obstruction of the bowels, are typically not present until large tumors have formed. A large tumor can sometimes be felt through the abdomen, and it can affect the bladder or vagina as well, leading to blood in the urine or unusual vaginal discharge. In advanced cases of colon cancer, the cancer metastasizes to the liver, causing enlargement of the liver, jaundice, and abdominal pain. Blood clots are another late-stage symptom.
Early detection is crucial for surviving this cancer. The disease can take years to develop, and if caught early enough, it can be surgically cured fairly simply. If the cancer has metastasized, extensive surgical treatment and chemotherapy are typically required and recovery is much less likely. Because colon cancer does not present with obvious symptoms until it is somewhat advanced, regular screening is recommended for people at risk.
The most common screening methods in the United States are the fecal occult blood test (FOBT), which checks for blood in the stool that is not visible, and endoscopy, in which a lighted probe is inserted into the rectum and colon to check for abnormalities. There are two types of endoscopy; sigmoidoscopy looks at the colon and lower rectum and is usually performed in conjunction with FOBT, while colonoscopy looks at the entire colon and rectum. If polyps are detected during a colonoscopy, they can be removed immediately.
There are two methods for describing the stages of colon cancer. The older version, known as the Dukes system, was developed in 1932 and divides the disease into four stages, A through D. In A, the tumor is confined to the intestinal wall. In B, it has grown past the intestinal wall. In C, the lymph nodes are affected, and D is characterized by distant metathesis. The TNM system describes the severity of the disease by assigning a different number to tumors (0-4), nodes (0-2), and metastases (0-1), where the higher number indicates a more advanced stage of cancer.