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Breast Cancer Genetics

When you or a relative is diagnosed with breast cancer it’s natural to wonder if there is a genetic connection, especially if there have been a few cases of breast cancer in the family. While there is a lot of talk about breast cancer running in families, only a small fraction of cases, between 5 and 10%, are considered hereditary. This is primarily caused by a gene that has mutated and been passed down to you. 

Understanding more about this genetic mutation can help you understand your risks for developing hereditary breast cancer. 

When is Breast Cancer Hereditary?

If you had one immediate family member diagnosed with breast cancer you're twice as likely than average to also receive a breast cancer diagnosis. And if you have two immediate family members with breast cancer you're 5 times more likely to develop it. It’s taken researchers many years of evaluating families and the genetic structure to understand the cause of hereditary breast cancer. Today you have options for reducing your risk that were not available to women only a few decades ago.

Men are also at an increased risk of breast cancer if they have a family history. However, they only represent about one percent of breast cancer cases. Whether you're male or female, you could have an increased risk, especially if you had a male or female immediate relative who was diagnosed.

The Genetics of Breast Cancer

BRCA1 and BRCA2 are the two genes that science currently recognizes as most associated with increased risk of breast cancer. Both are dominant, so unlike recessive genes, which may be dormant for a generation, if you have a BRCA gene mutation, it will always be active. It will increase your risk.

Those who have BRCA1 or BRCA2 gene mutation have a much higher likelihood of developing breast cancer by age 70. 

Other Genes that Can Increase Breast Cancer Risk

Genetics is an emerging science, and there's still a lot that researchers are figuring out about the genetics of breast cancer. While BRCA gene mutations appear to increase risk the most, other genes may play a role in increasing the risk of breast and other cancers.

Here are some syndromes commonly associated with mutations in certain genes:

  • Lynch syndrome has been connected with MLH1, MSH2, MSH6, and PMS2 genes
  • Peutz-Jeghers syndrome (PJS) has been connected with the STK11 gene
  • Ataxia telangiectasia (A-T) has been connected with the ATM gene
  • Hereditary diffuse gastric cancer has been connected with the CDH1 gene
  • Cowden syndrome (CS) has been connected with the PTEN gene
  • Li-Fraumeni syndrome (LFS) has been connected with the TP53 gene

Mutations in the PALB2 gene and CHEK2 gene may also increase risk.

Who Should Get Genetic Testing to Determine Cancer Risk?

Given the fact that only 1 in 400 people have a BRCA gene mutation, genetic testing isn't something that everyone must have as part of their routine health evaluations. But if you or your family members (on either side of the family) match one or more of these, genetic testing may be recommended for you:

  • Anyone in the family was diagnosed with breast cancer before age 50
  • By age 60, a woman in the family was diagnosed with triple-negative breast cancer
  • Three of more relatives, male or female, had breast cancer, pancreatic cancer, ovarian cancer, or aggressive prostate cancer
  • A male in the family had breast cancer at any age
  • A female in the family was diagnosed with ovarian cancer at any age
  • You have an Ashkenazi Jewish heritage along with any cancer in your family

Other reasons to consider genetic testing might include:

  • More than on generation on a single side of the family has had a cancer diagnosis
  • People in your family have developed any kind of cancer as a child or young adult
  • A family member had several types of cancer

A Minnesota Oncology genetic counselor can guide you through the risk factors that may make genetic testing a smart move for you. There are pros and cons of genetic testing. Some people would rather not know. Some people really need to know. It is vital that you prepare yourself mentally to know either way. A compassionate and knowledgeable genetic counselor will help you consider whether you should get the test, but ultimately it is up to you.

You Have a BRCA or Other Gene Mutation. Now What? 

Stay on Top of Exams and Mammograms

It is important to realize that having the BRCA gene mutation does not mean you’re definitely going to develop cancer. But it can help you and your doctors stay vigilant and look out for anything abnormal. Your doctor may recommend that you start getting mammograms before the average recommended age and they may add other types of imagery such as breast ultrasound and/or MRI.

The National Comprehensive Cancer Network (NCCN) recommends the following for those with a BRCA gene mutation:

  • Regular self-exams, which you are likely already doing at home.
  • A clinical breast exam every six to 12 months beginning at age 25. These are often part of an annual gynecologic exam. Talk to your doctor about how often you should have that type of exam performed.
  • Use 3D mammograms
  • Continue breast cancer screenings after age 75, if you choose. Typically after age 75 many women discontinue with mammograms as often as they had starting in their 40s.

Preventive Mastectomy: An Option Some Women Consider

Some women choose to have a preventive mastectomy or ovary removal. This is a very personal decision, and your genetic counselor can help you assess your feelings about such a procedure as well as the risks inherent in any surgery. You'll need to consider the cost of reconstruction after a double mastectomy, which could be expensive and may not be covered by insurance.

Other Proven Ways to Lower Your Risk of Developing Breast Cancer

While the gene mutation alone puts you at a higher risk of developing breast cancer, you can take action to reduce risks by living a healthy lifestyle. 

The NCCN recommends some lifestyle-related preventive measures like:

  • Eating a healthy diet filled with vegetables and fiber
  • Weight management
  • Physical activity - try to aim for 150 minutes of moderate exercise per week

The American Society of Clinical Oncology also recommends

  • Limiting alcohol consumption
  • Breastfeeding, if that is an option
  • Avoiding post-menopausal hormone supplements

The Mental-Emotional Side of Genetic Testing

Getting confirmation that you have an inherited gene mutation can be mentally and emotionally impactful. If you experience anxiety after receiving the news, talk to your genetic counselor for some coping techniques or seek the guidance of a therapist who can help you talk through your emotions and give you some tactics for handling anxiety.  

Where Can You Start?

If you think you or a family member might need genetic testing for breast cancer, then it is time to schedule an appointment with one of our genetic counselors to discuss whether there are indicators that maybe your family has a genetic mutation that leads to breast cancer, ovarian cancer and even other types of cancer. Even if you were tested several years ago, there are new tests coming available that may show you new information that wasn’t available before.

Learn more about our genetic counseling program.