Colon Cancer, The Genetic Factor
Colon cancer is the fourth most common cancer in the United States. In the US an estimated 130,000 men and women will develop colon cancer and more than 50,000 will die from it each year. The life-time risk for individuals to develop colon cancer is approximately 6%, but the risk increases to 18% among individuals who have a first degree relative (parent, sibling or child) with colon cancer.
What causes colon cancer?
When genes that normally control cell multiplication and growth mutate (change), the cells may multiply and grow without restraint. When cells grow without restraint inside the colon, a colon polyp develops. If additional genetic changes occur in that polyp, the polyp can turn cancerous and invade adjacent tissue and spread to distant sites. The sequence of events by which polyps form, become cancerous, invade nearby tissue and spread can and often does take years.
How does one acquire the mutations that cause colon cancer?
Inherited mutations will end up in every cell in the body, whereas acquired mutations will be present only in the original cell in which it occurred and in all the cells descended from that original cell. For example, the mutation may be restricted to the cells of the polyp or cancer.
Generally, acquired mutations tend to cause only one or a few colon polyps that can be removed by colonoscopy. (For further information, please see the article on colonoscopy.) Removing these polyps effectively prevents the progression from colon polyp to colon cancer.
On the other hand, inherited gene mutations present in every cell have a tendency to cause numerous (sometimes thousands) of colon polyps. These polyps may be too numerous or too large to be removed by colonoscopy. In addition, the progression from polyp to invasive cancer may be so rapid that even frequent colonoscopy is not adequate to remove the polyps and prevent colon cancer.
Finally, some cancers may develop directly from cells of the colon lining, without the development of polyps that can be recognized and removed. For this reason, surgical removal of the colon may be necessary to prevent colon cancer in patients with inherited forms of colon cancer.
What are hereditary colon cancer syndromes?
Familial adenomatous polyposis