By Shelley Kennedy, MS, CGC
Genetic testing has become an important tool in understanding breast cancer risk. Whether you’ve heard about BRCA1 and BRCA2 or are just beginning to learn about hereditary cancer, knowing the basics can help you and your family make informed choices. In this first part, we’ll explore what genetic testing is, how it works, and why it matters for breast cancer.
What is genetic testing?
To answer this, we need to review a bit of biology you may not have thought about since high school. Inside each cell of your body is your DNA – half inherited from your mother, the other half from your father. Genes are pieces of DNA that tell your body how to work. Each gene has a specific job. Some are responsible for things like hair colour or eye colour. Other genes play an important role in preventing cancer. If there is a change (called a mutation or pathogenic variant) in one of these cancer genes, resulting in the gene not working properly anymore, it can raise your risk of developing certain cancers.
Genetic testing can look at specific genes in your DNA for mutations. The two most common genes in cases of breast cancer are BRCA1 (BReast CAncer 1 Gene) and BRCA2 (BReast CAncer 2 Gene). In short, genetic testing can check to see if you were born with a change in a cancer-related gene that might affect your health or your family’s health.
How is it done?
The actual process is fairly straightforward: usually a blood test or sometimes a saliva (spit) sample is taken.
What exactly is hereditary breast cancer?
Hereditary (or ‘inherited’) breast cancer occurs when a gene with a mutation in it causing an increased risk for cancer is passed from one generation to the next within a family. Individuals who inherit this non-working gene have a higher chance of developing breast cancer and certain other cancers than the general population does.
How common is hereditary breast cancer?
It is currently estimated that about 1 in 10 cases of breast cancer is linked to inherited gene changes. This also means that most breast cancer, about 90%, is not inherited. These cases of breast cancer are often referred to as ‘sporadic’ – meaning they are the result of a combination of events including lifestyle, environment, genetics, and chance.
Unfortunately, breast cancer is a common cancer in women, with 1 in 8 women developing breast cancer in their lifetime. The biggest risk factors for developing breast cancer are being born female and aging. Did you know? About 85% of women diagnosed with breast cancer have no family history of the condition, meaning they are the first person in their family to be diagnosed.
What factors make breast cancer more likely to be a hereditary form?
Both personal factors and family history play a role.
Personal factors:
- Diagnosis of breast cancer at a young age
- Diagnosis of certain types of breast cancer (for example: triple negative breast cancer, which is more likely to be caused by an inherited mutation)
Family history – occurrences in a family that are considered a ‘red flag’ for hereditary breast cancer include:
- Many relatives with breast or ovarian cancer on the same side of the family (either the mother’s or the father’s side)
- A family member diagnosed with breast cancer at a younger age, usually before the age of 40
- Relatives who have both breast and ovarian cancer
- A person with breast cancer in both breasts
- Breast cancer in a male relative
- A breast cancer which is said to be ‘triple negative’.
- An ovarian cancer diagnosed before the age of 70 years
- Ashkenazi Jewish ancestry as mutations in the BRCA1 and BRCA2 breast cancer genes are more common in this population
How can genetic testing impact treatment for breast cancer?
If you have already been diagnosed with breast cancer, the results of genetic testing may change your treatment plan. For example, certain gene changes, like BRCA1 or BRCA2, can make some chemotherapy or targeted medicines work better.
The results can also guide surgery choices — for example, some people may choose to remove both breasts (not just the one with cancer) and/or their ovaries and fallopian tubes, if testing shows a high inherited risk.
Others opt to have enhanced screening for cancer. If you don’t have breast cancer, genetic testing can guide your prevention and screening options, like starting mammograms earlier, adding breast MRI scans, ultrasound or even considering risk-reducing surgery in advance of a cancer diagnosis.
What are some additional benefits of genetic testing?
If a mutation is found it can:
- Explain why you (or a family member) developed cancer
- Help identify which relatives may also be at risk — and which ones can be reassured they are not
- Sometimes provide information on risks for other types of cancer
- Understanding the basics of genetic testing is the first step in deciding if it is right for you.
But knowing what to expect before testing, how results are reported, and how to access testing can be just as important. In Part 2, we’ll walk through the practical side of genetic testing: what the results mean, how to get testing in Canada, and how genetic counsellors can help guide you through the process.
Important Note: This information is for general knowledge and does not constitute medical advice. If you have concerns about your risk of breast or ovarian cancer, consult with a healthcare professional for personalized guidance.
Shelley Kennedy is a Board-Certified Genetic Counsellor with over 21 years of clinical experience. Over the course of her career, she has worked in Canada, Australia, Saudi Arabia, and Qatar. She is a strong advocate for patient health and believes that knowledge is essential for making informed decisions that are right for each individual.
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