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 Genes are pieces of DNA (deoxyribonucleic acid)
inside our cells that tell the cell how to make the proteins the
body needs to function. DNA is the genetic “blueprint” in each cell.
Genes affect inherited traits passed on from a parent to a child,
such as hair color, eye color, and height. They can also affect
whether a person is likely to develop certain diseases, such as
cancer.
Changes in genes, called mutations, play an important role in the
development of cancer. Mutations can cause a cell to make (or not
make) proteins that affect how the cell grows and divides into new
cells. Certain mutations can cause cells to grow out of control,
which can lead to cancer. Still, only about 5% to 10% of all cancers
are thought to be strongly related to an inherited gene mutation.
Most cancers start because of acquired gene mutations
that happen during a person’s lifetime. Sometimes these gene changes
have an outside cause, such as exposure to sunlight or tobacco. But
gene mutations can also be random events that sometimes happen
inside a cell, without a clear cause.
Acquired mutations only affect the cells that grow from the mutated
cell. They do not affect all the cells in the person’s body. This
means all the cancer cells will have the mutations, but normal cells
in the body will not. Because of this, the mutations are not passed
on to a person’s children. This is very different from inherited
mutations, which are in every cell in the body – even the cells
without cancer.
What is genetic testing?
Genetic testing is the use of medical tests to look
for certain mutations in a person’s genes. Many types of genetic
tests are used today, and more are being developed.
Genetic testing can be used in many ways, but here we’ll focus on
its use in looking for gene changes linked to cancer.
Genetic testing for cancer risk
Predictive genetic testing is the type of testing used to look for
inherited gene mutations that might put a person at higher risk of
getting certain kinds of cancer. This type of testing might be
advised:
For a person with a strong family history of certain types of
cancer, to see if they carry a gene mutation that increases their
risk. If they do have an inherited mutation, they might want to have
tests to look for cancer early, or even take steps to lower their
risk. An example is testing for changes in the BRCA1 and BRCA2 genes
(which are known to increase the risk of breast cancer and some
other cancers) in a woman whose mother and sister had breast cancer.
For a person already diagnosed with cancer,
especially if there are other factors to suggest the cancer might
have been caused by an inherited mutation (such as a strong family
history or if the cancer was diagnosed at a young age). Testing
might show if the person has a higher risk of some other cancers. It
can also help other family members decide if they want to be tested
for the mutation.
For family members of a person known to have an
inherited gene mutation that increases cancer risk. Testing can
help them know if they need tests to look for cancer early, or if
they should take steps to try to lower their risk.
Most people (even people with cancer) do not need
this type of genetic testing. It’s usually done when family history
suggests there’s a cancer that may be inherited (see below).
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 Testing cancer cells for genetic changes
Sometimes after a person has been diagnosed with cancer, the doctor
will do tests on a sample of cancer cells to look for certain gene
changes. These tests can sometimes give information on a person’s
outlook (prognosis) and help tell whether certain types of treatment
might be useful.
These types of tests look for acquired gene changes only in the
cancer cells that are taken from the patient. These tests are not
the same as the tests used to find out about inherited cancer risk.
For more about this kind of testing and its use in cancer treatment,
see our information on specific types of cancer.
Who should have genetic testing?
Genetic counseling and testing may be recommended for people who
have had certain cancers or certain patterns of cancer in their
family. If you have any of the following, you might consider genetic
testing: Several first-degree relatives
(mother, father, sisters, brothers, children) with cancer
Many relatives on one side of the family who have had the
same type of cancer
A cluster of cancers in your family that are known to be
linked to a single gene mutation ( such as breast, ovarian, and
pancreatic cancers in your family).
A family member with more than 1 type of cancer
Family members who had cancer at a younger age than normal
for that type of cancer
Close relatives with cancers that are linked to rare
hereditary cancer syndromes
A family member with a rare cancer, such as breast cancer in
a male or retinoblastoma
Ethnicity (for example, Jewish ancestry is linked to ovarian
and breast cancers)
A physical finding that’s linked to an inherited cancer (such
as having many colon polyps)
A known genetic mutation in one or more family members who
have already had genetic testing
If you are concerned about a pattern of cancer in
your family, cancer you’ve had in the past, or other cancer risk
factors, you may want to talk to a health care provider about
whether genetic counseling and testing might be a good option for
you.
You need to know your family history and what kinds of tests are
available. For some types of cancer, no known mutations have been
linked to an increased risk. Other cancer types may have known
mutations, but there’s no way to test for them yet.
Family Cancer Syndromes gives you more information on the types
of cancers that may be linked to inherited genes.
Next steps
It’s important to find out how useful testing may be for you before
you do it. Talk to your health care provider and plan to meet with a
genetic counselor before the actual test. This will help you know
what to expect. The counselor can tell you about the pros and cons
of the test, what the results might mean, and what your options are.
[Taken from American Cancer Society
website] |
