Breast Cancer: Genetic Testing
Cancer is a disease of the genes. Most cancers develop because of genetic damage or
a change (mutation) that happens sometime during a person's lifetime. These are called
sporadic cancers. This means they occur by chance. These types of mutations only affect
the cells that grow from the original mutated cell.
Cancers that result from DNA damage that is passed on are called hereditary cancers.
These cancers tend to run in families. They cause hereditary cancer syndromes. But
only about 1 in 20 to 1 in 10 breast cancers are hereditary. If you may be at risk
for a hereditary cancer syndrome, genetic testing can be helpful. It can be used to
look for the gene changes linked to these syndromes.
Cancer and genes
The risk of developing cancer is higher in people who are born with certain gene changes
(mutations) that are passed on from their parents. These gene changes are in every
cell in their body. These changes are in areas of the DNA that affect cell division,
cell death, and the repair of damaged DNA.
Genes are pieces of DNA. They determine how your body looks, grows, and works. But
environmental factors affect the true outcome. For example, a person might have the
genetic potential to be 6 feet tall. But if they had poor nutrition as a child, they
may not reach that height. Or a person may have a genetic risk of developing breast
cancer. But whether they develop it may be affected by things they have contact with
during their lifetime.
Genes come in pairs. One pair is passed down (inherited) from your mother. The other
pair comes from your father. Genetic risks and outcomes can come from either parent.
Several genetic defects can cause an increased risk for breast cancer. The most common
defects are found on genes named BRCA1 (breast cancer gene 1) and BRCA2 (breast cancer
gene 2). A person who has inherited a harmful mutation in BRCA1 or BRCA2 is at higher
risk for breast cancer and some other types of cancer. But not all people with BRCA
1 or 2 mutations develop breast cancer. And not all people with breast cancer have
these mutations. Environmental factors can affect a person’s cancer risk, just as
they affect things such as height.
Common cancer syndromes that can be found with genetic testing
These are common gene mutations linked to cancer syndromes that can be found with
APC genemutations. These can cause familial adenomatous polyposis (FAP). This syndrome causes colon polyps,
colon and small intestine cancer, and cancers of the stomach, bone, skin, brain, and
BRCA 1 and BRCA 2 gene mutations. These are linked to hereditary breast and ovarian cancer syndrome. These mutations
can put a person at an increased risk for breast cancer. They also raise the risk
for ovarian, pancreatic, and prostate cancer.
MSH2, MLH1, MSH6, PMS1, and PMS2 gene changes. These can cause Lynch Syndrome (hereditary nonpolyposis colorectal cancer). This is
linked to many kinds of cancer. These include cancers that start in the colon, rectum,
endometrium, ovary, kidney, ureters, pancreas, small intestine, liver and biliary
tract, stomach, brain, and possibly breast.
PTEN gene changes. These cause Cowden syndrome. This is linked to breast, thyroid, endometrium, ovarian,
and other cancers.
TP53 and CHEK2 gene mutations. These cause Li-Fraumeni syndrome. They are also linked to an increased risk for many
cancer types, including breast cancer, sarcoma, leukemia, adrenal cancer, and brain
There are other rare gene mutations that can cause inherited breast cancer, too.
Deciding on genetic testing for cancer
Genetic testing for cancer should strongly be considered for a person if:
They have personal or family history that suggests a hereditary cancer syndrome, such
Cancers have been found at unusually young ages
Several close relatives who have had the same kind of cancer
One person has had multiple types of cancer
Cancer has been diagnosed in both organs when organs are found in pairs, such as both
breasts or both kidneys
There's evidence of other birth defects that are linked to certain cancer syndromes
Other family members have been tested and have genetic mutations that are linked to
A genetic test is available and has been proven to be accurate.
The results of testing can help the person make decisions about medical care.
Anyone considering genetic testing should first talk with a healthcare provider about
it. It's important to understand the limits of genetic testing and how the test results
might be used. You also need to discuss the costs and find out if your health insurance
will help pay for testing.
If you are considering genetic testing for cancer risks, you face many complex issues.
If you test positive, you may face difficult decisions about treatments to prevent
cancer. You may have increased fear and anxiety about developing cancer. You may have
concerns about losing your health insurance coverage. If you test negative, you may
also face difficult challenges, such as survivor guilt, if other family members have
But if you are anxious or considering treatments, such as preventive surgery based
on your family history, having the results may be very helpful. Because of these issues,
you should seek genetic counseling before, during, and after any genetic testing.
Remember, genetic testing cannot tell you everything about inherited cancers. A positive
result does not mean you will develop cancer. In most cases, other factors are involved.
In the same way, a negative result does not mean you won't get cancer. Genetic counselors
can talk to you about what a test will or will not tell you. They can help you decide
whether to get tested.
How is genetic testing done?
In most cases, a blood sample is needed to do genetic testing. Sometimes saliva, skin
cells, or cells swabbed from the inside of the cheek can be used. The sample is sent
to a lab where the testing is done. It usually takes a few weeks to get the results.
You will meet with the genetic counselor to go over the results and talk about what
they mean for you and your family.