Family History of Cancer: When Should You Consider Genetic Testing?

Having several family members with cancer can naturally raise questions about your own risk. However, a family history of cancer does not always mean that cancer is inherited.

Around 5% to 10% of cancers are thought to be linked to harmful genetic changes inherited from a parent. Cancer can also appear to run in families because of shared lifestyle or environmental factors, or simply by chance.

Genetic testing can help identify certain inherited genetic changes that may increase the risk of cancer. However, not everyone with a family history of cancer needs genetic testing. A doctor or genetic counsellor can assess your personal and family history to determine whether genetic testing may be appropriate for you.

What Does a Family History of Cancer Mean for Your Health?

A family history of cancer means that one or more of your biological relatives have had cancer. The type of cancer, age at diagnosis and number of affected relatives can all provide important information. Certain patterns may raise the possibility of hereditary cancer, such as:

• Several close family members have the same or related types of cancer.
• Cancer occurs at a younger age than is typical for that type of cancer.
• One person develops more than one primary cancer.
• A family member has a rare cancer, such as male breast cancer.
• Breast and ovarian cancers occur in the same family.
• Colon and endometrial cancers occur in the same family.
• A known inherited cancer-related gene change has already been identified in the family.

These patterns do not necessarily mean that cancer is hereditary. A doctor or genetic counsellor can review your personal and family history to determine whether genetic counselling or testing may be appropriate.

It is also important to remember that inheriting a cancer-related gene change does not mean you will definitely develop cancer. It means your risk may be higher than that of the general population.

When Should You Consider Genetic Testing for Hereditary Cancer?

Genetic testing may be considered when your personal or family history suggests a possible hereditary cancer syndrome. A doctor or genetic counsellor can assess your history and help determine whether testing may be appropriate.

You may want to discuss genetic testing with a doctor or genetic counsellor if:

• A close blood relative has a known harmful genetic change linked to cancer risk.
• Several close relatives have had cancer, particularly the same or related types of cancer.
• Cancer was diagnosed at a younger age than is typical for that type of cancer.
• The same or related cancers occur in multiple generations of a family.
• You or a relative has had more than one primary cancer.
• You or a family member has a type of cancer that can be associated with inherited genetic changes.
• A family member has had a rare cancer, such as male breast cancer.

When possible, genetic counselling and testing generally begin with a family member who has had the cancer of concern. If a harmful inherited gene change is identified, other blood relatives can then be tested for that specific genetic change. This can provide more useful information than testing an unaffected relative first.

Which Types of Cancer Are Most Commonly Linked to Inherited Gene Mutations?

Certain inherited gene changes are associated with a higher risk of specific cancers. Some commonly discussed examples include:

These are only examples. Many genes can be involved in hereditary cancer risk, and the appropriate test depends on your personal and family history.

How Genetic Testing for Cancer Works: Process, Benefits and Limitations

Genetic testing for cancer usually involves several steps:

1. Review of medical and family history: A doctor or genetic counsellor reviews your personal and family history, including the types of cancer diagnosed and the age at diagnosis. This helps determine whether genetic testing may be appropriate.
2. Genetic counselling: Before testing, a genetic counsellor explains the purpose of the test, possible results and their potential implications for you and your family.
3. Sample collection: Genetic testing usually requires a blood or saliva sample. The sample is sent to a specialised laboratory for analysis.
4. DNA analysis: The laboratory examines specific genes for genetic changes that may be associated with an increased risk of certain cancers. Depending on your history, testing may focus on one gene or several genes.
5. Results and interpretation: Results may identify a harmful genetic change, no harmful genetic change, or a variant of uncertain significance (VUS). A doctor or genetic counsellor helps interpret the result in the context of your personal and family history.

Benefits of Genetic Testing for Cancer

Genetic testing can provide several potential benefits:

• Identifies inherited cancer risk: Testing may identify harmful genetic changes that increase the risk of certain cancers.
• Helps guide screening: If an increased risk is identified, your doctor may recommend specific or earlier cancer screening.
• Supports risk-reduction decisions: Depending on the genetic change, you may have options to reduce your risk of developing certain cancers.
• Provides information for family members: If an inherited genetic change is found, biological relatives can discuss targeted testing to determine whether they have inherited the same change.
• May help guide treatment: For people who have cancer, some inherited genetic findings may provide information that can help guide treatment decisions.

Limitations of Genetic Testing for Cancer

Genetic testing also has some limitations:

• It cannot predict cancer with certainty: Having a harmful genetic change does not mean that you will definitely develop cancer.
• A negative result does not eliminate cancer risk: You may still have an increased risk because of your family history or other genetic and environmental factors.
• Some results may be uncertain: A variant of uncertain significance means that there is not enough evidence to determine whether the genetic change affects cancer risk.
• Not all genetic changes are detectable: A test only identifies genetic changes that it is designed and technically able to detect.
• Results may cause emotional concerns: Learning about an increased inherited cancer risk can cause anxiety or uncertainty for some people.

Can Hereditary Cancer Be Prevented?

An inherited cancer risk cannot always be prevented, but knowing about it can help with risk management and early detection.

Depending on the gene change and the type of cancer involved, your doctor may recommend:

• Starting cancer screening at a younger age.
• Having screening more often.
• Taking medicines that may lower cancer risk in selected situations.
• Considering risk-reducing surgery in certain high-risk cases.
• Making lifestyle changes, such as avoiding tobacco and maintaining a healthy weight.

The right approach depends on the specific gene change and your personal circumstances. A positive genetic test does not mean that cancer is inevitable.

Final Thoughts

A family history of cancer does not mean you will develop cancer. However, repeated cases of cancer, a younger age at diagnosis or certain cancer patterns in a family may point to an inherited cancer risk.

Genetic testing can help identify some inherited genetic changes and inform screening and risk-reduction decisions. If you have a strong family history of cancer, speak with a doctor or genetic counsellor to understand whether testing is right for you.

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