Health Library

Cancer is a disease of the genes. Most cancers develop as a result of genetic damage
or a mutation that happens sometime during a person’s lifetime. These are called sporadic cancers (occurs 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 is called hereditary cancers. These cancers tend to run in families. They cause
hereditary cancer syndromes, but overall are linked to only about 5% to 10% of all
cancer cases. Genetic testing can be used to look for the gene changes that are linked
to these hereditary cancer syndromes in people thought to be at risk for having one
of them.

Cancer and genes

The risk of developing cancer is higher in people who are born with certain genetic
defects that are passed on from their parents and found in every cell in their body.
These defects occur in areas of the DNA that affect cell division, cell death, and
the repair of damaged DNA.

The National Cancer Institute describes genes as “nature’s blueprints for every living
thing.” Genes determine your body’s potential for function and growth. Environmental
factors influence the outcome. For example, a woman might have the genetic potential
to be 6 feet tall. However, if she has poor nutrition as a child, she may not reach
that potential. Similarly, a woman may have a genetic risk of developing breast cancer.
Whether she develops it or not may be influenced by environmental exposures she has
during her lifetime.

Genes come in pairs. One set is passed down (inherited) from your mother and the other
set from your father. Genetic risks and potential can come from either parent.

A number of genetic defects can result in an increased risk for cancer. For instance,
for breast cancer, the most common defects are found on genes named BRCA1 (breast
cancer gene 1) and BRCA2 (breast cancer gene 2). A woman who has inherited a harmful
mutation in BRCA1 or BRCA2 is at higher risk of developing breast cancer and some
other types of cancer than a woman who does not have such a mutation.

Researchers at the National Human Genome Research Institute have developed tests using
DNA microchip technology that can distinguish between hereditary and sporadic forms
of cancer. Today, more than 50 different hereditary cancer syndromes can be identified
with genetic testing. 

Common cancer syndromes that can be identified with genetic testing

These are some of the more common gene mutations that are linked to cancer syndromes and
can be found with genetic testing.

APC gene mutations can cause familial adenomatous polyposis or FAP. This syndrome causes colon
polyps, colon and small intestine cancer, and cancers of the stomach, bone, skin,
brain, and other tissues. 

BRCA 1 and BRCA 2 gene mutations are linked to hereditary breast and ovarian cancer syndrome. These mutations
can put a person at an increased risk for breast (in both men and women), ovarian,
pancreatic, prostate cancer.

MSH2, MLH1, MSH6, PMS2, and EPCAM gene changes can cause hereditary nonpolyposis colorectal cancer, also called Lynch Syndrome.
This is linked to many different kinds of cancer, including those that start in the
colon, rectum, endometrium, ovary, kidney, pancreas, small intestine, liver and biliary
tract, stomach, brain, and breast

PTEN gene changes cause Cowden syndrome, which is linked to breast, thyroid, endometrium, and
other cancers.  

TP53 gene mutations cause Li-Fraumeni syndrome, and are linked to an increased risk of many
cancer types, including breast cancer, sarcoma, leukemia, and brain tumors. 

Deciding on genetic testing for cancer

Genetic testing for cancer should strongly be considered in people with all of the
following:

• A personal or family history that suggests a hereditary cancer syndrome is present,
  such as:

  • 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
    cancer

• 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

It’s strongly recommended that anyone considering genetic testing first talk to a
professional about it. It’s important to understand the limitations of genetic testing
and how the test results might be used before getting tested. You also need to discuss the costs and whether 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
tested positive.

However, 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 always 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 particular test will or will not tell you,
and 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, but 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 actual 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 figure out what
they mean for you and your family.