What Do We Know About Heredity And Colon
Cancer?
Colon cancer, a malignant tumor of the large intestine,
affects both men and women. In the year 2000, there were an
estimated 130,200 cases diagnosed.
The vast majority of colon cancer cases are not hereditary.
However, approximately 5 percent of individuals with colon
cancer have a hereditary form. In those families, the chances
of developing colon cancer is significantly higher than in the
average person.
Scientists have discovered several genes contributing to a
susceptibility to two types of colon cancer:
- FAP (familial adenomatous
polyposis)
So far, only one FAP gene has been discovered - the APC
gene on chromosome 5. But over 300 different mutations of
that gene have been identified. Individuals with this
syndrome develop many polyps in their colon. People who
inherit mutations in this gene have a nearly 100 percent
chance of developing colon cancer by age 40.
- HNPCC (hereditary nonpolyposis colorectal
cancer)
Individuals with an HNPCC gene mutation have an estimated
80 percent lifetime risk of developing colon or rectal
cancer. However, these cancers account for only three to
five percent of all colorectal cancers. So far, four HNPCC
genes have been discovered:
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