Genetics and colon and rectal cancer
Colon and rectal cancers are sometimes hereditary.
Though most cases of colon and rectal cancer occur sporadically, it is estimated
that 5% to 6% of all cases can be explained by a specific genetic susceptibility.
A person who is diagnosed with colon or rectal cancer and who has a family history
of the disease is more likely to have inherited a cancer gene than a person with
no family history of colorectal cancer.
About 5% to 10% of people who develop colorectal cancer do so because they have
inherited gene changes. The 2 most common inherited syndromes are familial
adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC).
FAP is caused by changes in the APC gene that a person inherits from his or her
parents. FAP accounts for about 1% of all colorectal cancers.
People with FAP often develop hundreds or thousands of polyps in their colon and
rectum, usually in their teens or early adulthood.
Cancer usually develops in 1 or more of these polyps as early as age 20.
By 40, almost all people with this disorder will have developed cancer if the colon
is not removed.
Slightly more common than FAP is HNPCC, also known as Lynch syndrome. HNPCC accounts
for about 3% to 5% of all colorectal cancers. It can be caused by inherited changes
in a number of different genes that normally help repair DNA damage.
HNPCC tends to affect people when they are relatively young. Those with the syndrome
develop polyps, but only a few— unlike those with FAP, who may have hundreds.
The lifetime risk of colorectal cancer in people with this condition may be as high
as 80%.
Although genetic testing for colon and rectal cancer is possible and available,
it is only an adjunct to the clinical management of persons at risk for colon cancer
and patients with colon cancer.
Learn about the
signs and symptoms of colon and rectal cancer