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Colon
Cancer & Heredity
1. How common is colorectal cancer?
Excluding skin malignancies, colorectal cancer is the third
most common cancer diagnosed among American men and women.
(The leading cancers for men are lung and prostate cancers;
for women, the leading cancers are lung and breast cancers.)
About 130,000 new cases of colorectal cancer are diagnosed
each year. Six percent of all Americans, 1 out of every
17, will develop colorectal cancer.
2. How often is colorectal cancer
hereditary?
Though most cases occur sporadically, it is estimated that
5 to 10 percent of all colorectal cancers are explained
by a specific genetic susceptibility. A person who is diagnosed
with colorectal 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.
3. What is hereditary nonpolyposis
colorectal cancer (HNPCC)?
HNPCC is a syndrome that accounts for approximately 5 percent
of all colorectal cancer diagnoses. The syndrome is caused
by mutations in specific genes, which are described below.
Families with HNPCC typically have:
• Three or more closely related family members diagnosed
with colorectal cancer
• Affected family members in two or more generations
• At least one person with colorectal cancer diagnosed before
the age of 50
The average age of colorectal cancer onset in families with
HNPCC mutations is 45 years. Though colorectal cancer is
the most common malignancy reported in families with HNPCC,
the syndrome is also associated with an increased risk for
cancers of the uterus, ovaries, stomach, small intestine,
biliary system, pancreas, and urinary tract.
There are families with strong histories of colorectal cancer
but in whom HNPCC mutations have not been detected. These
families may carry mutations in genes yet to be identified,
or there may not be a mutation at all, the cancer history
possibly being explained by ill chance.
See About Hereditary Nonpolyposis Colorectal Cancer for
more information.
4. What are familial adenomatous
polyposis (FAP) and MYH gene mutation?
There are other rare forms of hereditary colon cancer. One
of these is called familial adenomatous polyposis. In this
condition, children develop hundreds or thousands of polyps
in the colon at a very early age.
These children will almost always go on to develop colon
cancer by age 40. There are two other, milder hereditary
colorectal syndromes, known as attenuated familial adenomatous
polyposis (AFAP) and MYH-associated polyposis. Less is known
about these two recently discovered syndromes.
For more information about these other hereditary colon
cancer syndromes, see About Familial Adenomatous Polyposis.
5. What are the possible benefits and risks of gene testing?
You should think about the following benefits and risks
before you undergo genetic testing.
Benefits
• Genetic test results may allow for a more accurate assessment
of a person's cancer risk. If the results are positive,
doctors can screen earlier as described above to look for
colorectal cancer and other HNPCC-associated cancers. If
the results are negative, individuals may not have to screen
as aggressively.
• If a mutation is identified, genetic testing and/or early
cancer screening can be offered to other at-risk family
members.
• There is no physical risk involved in genetic testing,
other than that of a routine blood draw.
Risks
• Genetic testing can be emotionally difficult regardless
of the results.
• If a mutation is found, relatives who have not had genetic
testing may make assumptions about their own genetic status.
• The costs associated with cancer screening and prevention
for people with mutations may or may not be covered by their
health insurance provider.
• There is also the possibility of employer discrimination
or insurance provider discrimination based on genetic test
results. Insurers may seek higher premiums or cancel/deny
policies for individuals with pre-existing genetic conditions.
In New York State, a person's genetic test results cannot
be given to anyone else without the written permission of
the person who is tested. Genetic testing at Memorial Hospital
is generally offered within the context of a research study.
Test results are therefore stored in research files that
are kept separate from regular medical records. We have
obtained certificates of confidentiality from the National
Institutes of Health to protect the research information
contained in these files.
Should a person receive genetic counseling for cancer risk
based solely on family history however, that information
will become part of their medical record. Should a person
choose to share their genetic test results with another
healthcare professional, that information may also become
part of their medical record.
At present, we are not aware of any instances of discrimination
against families who have received genetic testing as part
of research studies at Memorial Hospital.
6. What if I have a family history of colorectal
cancer but don't want to undergo genetic testing?
Even if you don't want to take part in a study and/or receive
genetic testing, you should talk to your doctor about your
family history of colorectal cancer. If any one of your
close relatives has had colorectal cancer, you have an increased
chance of developing colorectal cancer as well. Speak with
your doctor about your family history of colorectal cancer
and discuss appropriate screening recommendations to lower
your risk of developing this disease.
Even if you don't wish to have genetic testing, you are
welcome to make an appointment at the Clinical Genetics
Service to discuss your family history and learn about cancer
screening recommendations.
7. What if I have a family history
of colon cancer in older members of my family?
Your family history can serve as a guide to help you determine
your risk for colon cancer. Your gastroenterologist, internist,
or cancer geneticist can provide you with guidelines based
on your family history. For example, in many families we
will recommend that colonoscopy screening begin ten years
before the age of onset of cancer for the youngest affected
person in your family. There are also research studies involving
diet and "chemoprevention" measures that you may
consider.
8. What other forms of screening
are available for colon cancer?
At Memorial Sloan-Kettering, colonoscopy is considered the
"gold standard" for colon cancer screening. During
a colonoscopy, the doctor passes a thin flexible tube through
the anus to look inside the colon.
In other settings, doctors may perform sigmoidoscopy, which
visualizes only the last third of the colon. Newer tests
such as "virtual colonoscopy" are being developed
that allow imaging of the colon.
If someone else in your family has already tested positive
for a gene mutation, you may be tested for the specific
mutation found in their sample. If you have tested negative
for a mutation that's known to run in your family, no further
testing is needed.
For more information on cancer syndromes related to the
APC and MYH genes, see About Familial Adenomatous Polyposis.
http://www.mskcc.org/mskcc/
html/8624.cfm
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