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The Genetics of Hereditary Cancer


Genetic testing looks for specific inherited changes (mutations) in a person’s chromosomesgenes, or proteins. Genetic mutations can have harmful, beneficial, neutral (no effect), or uncertain effects on health. Mutations that are harmful may increase a person’s chance, or risk, of developing a disease such as cancer. Overall, inherited mutations are thought to play a role in about 5 to 10 percent of all cancers.

With only 5-10% of cancers being hereditary, is genetic testing relevant to me?

A person with hereditary cancer is born with a genetic mutation that makes them more likely to develop cancer in their lifetime. A genetic mutation could be inherited from your mother, father, or both.

How do I understand if cancer runs in my family?

Cancer can sometimes appear to “run in families” even if it is not caused by an inherited mutation. For example, a shared environment or lifestyle, such as tobacco use, can cause similar cancers to develop among family members. However, certain patterns—such as the types of cancer that develop, other non-cancer conditions that are seen, and the ages at which cancer typically develops—may suggest the presence of a hereditary cancer syndrome. 

What information is helpful?

The features of a person’s personal or family medical history that, particularly in combination, may suggest a hereditary cancer syndrome include:

  • Cancer that was diagnosed at an unusually young age
  • Several different types of cancer that have occurred independently in the same person
  • Cancer that has developed in both organs in a set of paired organs, such as both kidneys or both breasts
  • Several close blood relatives that have the same type of cancer (for example, a mother, daughter, and sisters with breast cancer)
  • Unusual cases of a specific cancer type (for example, breast cancer in a man)
  • The presence of birth defects, such as certain noncancerous (benign) skin growths or skeletal abnormalities, that are known to be associated with inherited cancer syndromes
  • Being a member of a racial/ethnic group that is known to have an increased chance of having a certain hereditary cancer syndrome and having one or more of the above features as well

Why is it important for ME to understand my cancer family history?

Certain people with a significant family history of cancer may want to consider genetic counseling and testing. Sometimes the result of genetic testing could affect your treatment plan and/or follow-up care. If an inherited genetic mutation is found, family members should have the option to consider testing in order to individualize cancer screening methods or cancer prevention strategies. 

Does someone who inherits a cancer-predisposing genetic change always get cancer?

No. Even if a cancer-predisposing mutation is present in a family, it does not necessarily mean that everyone who inherits the mutation will develop cancer. Once the genetic mutations that cause many of the known hereditary cancer syndromes have been identified, genetic testing can confirm whether a condition is, indeed, the result of an inherited syndrome. Genetic testing is also done to determine whether family members without obvious illness have inherited the same mutation as a family member who is known to carry a cancer-associated mutation.

What can I do to learn if my immediate family and I have a cancer predisposing genetic change?

The first step is understanding your family history. Please complete the following Family History Questionnaire following this page. Include detail of your family history of cancers and other significant medical illnesses. 

How is genetic testing done?

Testing is done on a small sample of body fluid or tissue—usually blood, but sometimes saliva, cells from inside the cheek, or skin cells. The sample is then sent to a laboratory that specializes in genetic testing. The laboratory returns the test results to the doctor or genetic counselor who requested the test. It usually takes several weeks or longer to get the test results.

Will my results apply to myself AND my family, my children?

Identifying at-risk family members is one of the most important benefits of genetic testing. If you have a genetic alteration, your immediate family members could have a 50% chance of having the same alteration. Other relatives may also be at risk. 

Additional Information

Knowledge is Power! It is our goal to provide the most current, complete care options for you. It is also our goal to help families understand what options are available for cancer risk assessment and risk reduction strategies. 

You can find additional helpful information and watch videos regarding genetic testing on the following websites: