Types of genetic testing available for breast cancer

Types of genetic testing available for breast cancer
Breast cancer is the most common form of cancer diagnosed in women in the US. Like many types of cancer, the risk for breast cancer is heavily influenced by a person’s genetics. Whether you have a family member with breast cancer or you want to know more about its causes, let’s understand what science has to say about the genetics behind the disease.
Written by Dave Gennert, PhD candidate
Orchid offers advanced genetic testing for couples who want their child to have the best shot of a healthy life. “Genetics for Humans” is where we unpack how genetics impacts our everyday lives and the latest tools to help you build a healthier family.

What is breast cancer, and how does it impact individuals?

The breast is made up of several types of tissue that can become cancerous– lobes produce milk and ducts carry the milk to the nipple.Breast cancers can vary in their aggressiveness, from non-invasive types like ductal carcinoma in-situ (DCIS), which is restricted to the duct tissue and is generally non-life threatening, to highly invasive carcinomas that spread quickly to neighboring tissues, the lymph nodes, and other organs.

The good news is that, even though the number of new cases has remained steady since 2007, the number of deaths in the US due to breast cancer has decreased 40% since 1989. Improved screening, preventative surgery, and medications have helped reduce the mortality rate. In 62% of cases, breast cancer is detected early (while the cancer has not spread to other tissues), which has a 99% survival rate. All invasive breast cancers together have a 5-year survival rate of 91%.

How common is breast cancer?

In the US, breast cancer is the most common form of cancer in women, affecting about 1 in 8 women during their lifetime. In 2020 alone, 276,480 American women were estimated to be diagnosed with breast cancer.

Ethnicity also plays a role in the prevalence of breast cancer. Although white Americans have the highest incidence rate of breast cancer, Black Americans have the highest mortality rate. Aside from the socioeconomic factors that affect lifestyle and the healthcare Black individuals receive, they are also more likely to develop more aggressive forms of breast cancer.

Men can also be diagnosed with breast cancer. Approximately 1% of breast cancer diagnoses are in men. Male breasts have the same types of tissues as in female breasts, meaning they are susceptible to cancer as well, but have much lower risks than women.

Does breast cancer run in families?

Yes, breast cancer has a large contribution from genetics and is known to run in families. An estimated 31% of a person’s risk for breast cancer is believed to be determined by genetics. A family history of breast cancer is actually one of the major risk factors for developing breast cancer. A first-degree relative diagnosed with breast cancer doubles one’s own risk; having two affected first-degree relatives triples the risk. “Hereditary” breast cancer – that is, cases often occurring in multiple generations of a family– makes up around 5-10% of all breast cancer cases.

What are the genetic causes of breast cancer?

The genetic causes of breast cancer can largely be broken down into two categories: high-risk single gene mutations and a combination of many genetic variants.

Single-gene mutations

The genetic mutations that lead to families with high incidences of breast cancer are typically high-risk mutations that often lead to more aggressive and earlier-onset forms. Mutations in theBRCA1 and BRCA2 genes are most commonly known to increase the risk of developing breast cancer.

Individuals with a harmful mutation in BRCA1 have between a 44-79% chance of developing breast cancer; those with a harmful mutation in BRCA2 have between a 31-77% chance of developing breast cancer. Though that represents a very high added risk, mutations in those genes are relatively uncommon, only appearing in 1 in 400 individuals in the population.

Certain populations, though, are more likely to have BRCA1/2 mutations. 1 in 40 Ashkenazi Jewish people, for example, have a harmful mutation in one of these genes.

Harmful mutations can also appear in other genes that increase the risk of breast cancer. A variety of mutations in genes such as CHEK2, ATM, and PALB2, among others, have been each shown to increase overall risk.

Families with a strong history of breast, ovarian, prostate, or pancreatic cancer may benefit from genetic testing to find potential high-risk mutations in these high-risk genes. Talking to a cancer genetic counselor may help determine if single-gene testing is appropriate for you and your family.

Combination of many genetic variants

Most cases of breast cancer, though, aren’t caused by single high-risk mutations. Instead, genetic risk is a combination of many genes and genetic markers across the genome.

Throughout the genome, the DNA sequence variants that make each person unique also work together to increase or decrease each person’s risk for developing a number of conditions, including breast cancer.

Is there a genetic test for breast cancer?

Yes, there are tests available to measure the genetic predisposition to breast cancer. Testing can be broken down into two types, depending on which genetic factors are measured:

  • Testing for specific high-risk single-gene mutations
  • Advanced genetic predisposition screening for increased risk
High-risk single-gene testing

A strong family history of breast or other cancers may indicate a high-risk single-gene mutation as a cause. As inherited breast cancer is often more aggressive with earlier onset, those with inherited cancer risk may wish to seek out genetic counseling to see if single-gene testing is appropriate.

Testing for breast cancer single-gene mutations can help determine if one of these genes is contributing to a family’s high risk for cancer. The results from these tests may affect the monitoring plan for breast cancer, lifestyle changes to prevent disease, and other preventative measures that you and your doctor want to pursue.

Advanced genetic screening

If you are concerned about cancer predisposition but don’t have strong indicators for single-gene cancer mutations, such as family history or ethnicity, genetic screening may help assess the risk of developing cancer. Even if single-gene genetic screening does not reveal a high-risk mutation, the cumulative genetic risk for cancer caused by other variants in the genome may confer increased overall risk. Genetic screening can tell you if you are more or less likely to develop breast cancer than the average person based on your genetic background.

This is done by factoring in all the variants across the genome that we know increase the risk for breast cancer. Individually, each of these variants has a low impact on risk, but when combined, they can lead to significant risk for disease.

Taken together, these risk variants can provide a genetic risk score, unique for each person. An individual’s risk score will tell them their relative risk compared to the general population.A recent study on over 140,000 people found that 1.5% of the population is three times more likely to develop breast cancer based on screening for these genetic markers. The researchers also found that such a screen identified 0.1% of women to be over five times as likely to develop breast cancer compared to the general population.

With Orchid’s advanced genetic testing, you can get a sense of your genetic predisposition to breast cancer and remove some of the guesswork on what you can pass on to your future children.

What actions can I take based on the information from a genetic test for breast cancer?

If you or your future child has an elevated genetic risk for breast cancer, the risk of developing breast cancer at some point in life can be over five times higher than in the general population.

The useful thing about your results is that if you identify certain genetic vulnerabilities that can impact you or your future children, you can potentially do something about it and mitigate these risks. Ways you can act on your results include:

  • Seek cancer genetic counseling early.  If you have a personal or strong family history of early-onset or more aggressive forms of breast cancer, a genetic counselor can help you understand the risks for you and your family. Your health care team can integrate your family history of cancer, ethnic background, and breast cancer genetic risk score to better assess your overall risk.
  • Consider increased cancer screening and prevention strategies.  If detected in an early stage, while the cancer has not spread, breast cancer has a 99% survival rate.  An elevated genetic risk may call for increased screening in order to catch breast cancer early, which may include imaging tests such as mammography or breast MRI and doctor’s breast exams.
  • Offset genetic risks with healthy lifestyle choices.  Although genetics plays a large role in cancer risk, lifestyle factors contribute to breast cancer risk.  Smoking, low physical activity and exercise, and drinking alcohol have been associated with a higher risk of breast cancer.
  • Embryo screening to reduce your child’s potential genetic risks.  Embryo screening allows you to assess each embryo’s genetic risk for breast cancer and other common conditions. This allows you to prioritize the transfer of embryos with the lowest genetic risk and thus reduce your future child’s genetic risks.

Key takeaways

  • Breast cancer is a common form of cancer, representing the leading cause of cancer in women in the US.
  • Age, family history, and genetic background are the main risk factors for developing breast cancer.
  • Advanced genetic testing can now quantify the genetic component to breast cancer for you and your family.
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Orchid offers advanced genetic testing for couples planning on building their family. We use advanced tools and smart, caring humans to help you give your future children the best shot of a healthy life. Conceive with greater confidence and peace of mind
3/3/2021
Genetics
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