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Assessing Your Risk for Hereditary Breast & Ovarian Cancers

A Change in a Gene

Hereditary cancers are caused by gene mutations that are passed down through a family. A
mutation is an alteration, or change, in a gene that causes the gene not to work correctly.

A genetic test can show whether you carry a gene mutation that puts you at a higher risk for
certain cancers including breast cancer or ovarian cancer.

Read this information to learn more about hereditary breast and ovarian cancers. It explains things
to think about before having genetic testing and what test results may mean for you and your
family. Use this information to help you decide whether you may benefit from a genetic test.

If you have questions about this information, talk with your health care provider.

Causes of Breast or Ovarian Cancer

Researchers do not know exactly what causes most cases of breast or ovarian cancer. It happens
when cells collect genetic changes and begin to divide and grow faster than healthy cells do. The
cells then build up and form a tumor.

In the general population, around 12 out of 100 women (12 percent) get breast cancer and about 1
to 2 out of 100 women (1 to 2 percent) get ovarian cancer. These cancers usually develop after
age 50. Although it is rare, men can get breast cancer too.

Most breast and ovarian cancers are sporadic. This means they happen by chance. Sporadic
cancers are due mostly to aging, the environment and lifestyle choices. See Figures 1 and 2.

Of those who get breast cancer, only about 5 to 10 percent are hereditary, or inherited. Of those
who get ovarian cancer, only about 15 to 20 percent are hereditary, or inherited. Gene mutations that are passed from parents to children can cause hereditary cancers. If you have a gene
mutation, your risk for certain cancers may be higher. However, having a mutation does not
guarantee that you will get cancer.

Even when several family members have the same kind of cancer, a mutation is not always the
cause. More often, the cancer is familial. Familial means something that happens more often in a
family than would be due to chance alone. However, it is not caused by a mutation in a single

Genetic factors may play a role in familial cancers. However, families share many things besides
their genes, including environmental factors. For example, family members may eat the same
kinds of foods. They may live in the same kind of environment. They may have similar jobs. These
things, in combination with multiple genetic factors rather than a single gene mutation, might
cause cancer in a family.

Click here to view a graphic of genetics and its connection with breast cancer.