Understanding the Genetics of Breast Cancer

Have you or a relative been diagnosed with breast cancer? You may be curious about whether it runs in your family. Like many health conditions, breast cancer can have a genetic link. But this happens in only about 5 to 10% of cases. When cancer runs in the family, it's chiefly because one or more genes have mutated. Once a gene mutates, that person has a chance of passing it down to their children.

Having a particular gene mutation doesn't always mean cancer. Most people who develop breast cancer have no family history of the disease and did not inherit a gene mutation. 

Understanding the genetic mutations that can cause breast cancer helps you and your family better understand the personal risk of developing breast cancer.

When Can Breast Cancer Be Hereditary?

If something is hereditary, it can be inherited from one or both of your birth (biological) parents. You're twice as likely to develop breast cancer if you have an immediate family member with breast cancer; five times more likely if two family members have been diagnosed.

Remember that men can get breast cancer, too. About 1% of breast cancer cases occur in men, and they can also pass on gene mutations to their children. Men also have an increased risk if they have a family history of breast cancer.  

Researchers have isolated specific gene mutations responsible for hereditary breast cancer. This research can help you find out if you have one or more gene mutations and let you plan accordingly to reduce your risk.

Understanding Breast Cancer Genetics

You don't have to be a geneticist to understand the basics of breast cancer genetics. Genes are short segments of DNA, and DNA holds the instructions for building proteins. Proteins control the structure, growth, and function of all the cells in our bodies.

When DNA gets an incorrect set of instructions, cells don't grow or function correctly. Any mistake in a gene will be in all the cells that contain that gene. These mistakes can be inherited, or they can happen over time as we age. It doesn't mean they will be inherited or happen over time, only that they could be.

Gene mutations that are known to cause an increase in breast cancer risk are BRCA1 and BRCA2 (BRestCAncer). You may have heard breast cancer doctors call them "brack-uh" or "breck-uh" genes. Everyone has these genes, and their function is to repair cell damage and keep breast and ovarian cells growing normally.

Genes come in pairs in your DNA strands. One comes from each parent. However, only one gene in a gene pair can be active. One gene is dormant, and the other is dominant. If a gene is dormant, it may do nothing right now, but you can pass it down to your children. Dominant genes are active in you and can also be passed to your children. In the case of BRCA genes, they're always dominant. That means BRCA gene mutations will always increase your risk of getting breast cancer before age 70.

Genetic information leads to improved cancer prevention

The scientific community's understanding of genetics has skyrocketed since the late 1990s. A lot of our understanding is new and continues to change. Researchers are still trying to understand how gene mutations increase risk. The BRCA gene mutations are the major ones to be aware of, but other mutations may play a role in increasing breast cancer risk.

Who's at Risk for Developing Breast Cancer?

You are much more likely to have a breast-cancer-related genetic mutation if you have any of these conditions:

  • Blood relatives (grandmothers, mother, sisters, aunts) on either side of the family who had breast cancer diagnosed before age 50
  • Both breast and ovarian cancer on the same side of the family or in one person
  • A relative(s) with triple-negative breast cancer by age 60
  • Family members with cancers of the breasts, prostate, pancreas, stomach, uterus, thyroid, colon, or who has sarcoma or melanoma
  • Women in your family with cancer in both breasts or ovarian cancer at any age
  • Cancer in multiple generations on one side of your family
  • Family history of child or young adult cancers
  • Ashkenazi Jewish/Eastern European heritage
  • Black and diagnosed with breast cancer before age 35
  • Male family member with breast cancer at any age
  • You know there are abnormal breast cancer genes in your family

Risk can also be measured as to how likely you are to develop breast cancer. The average American woman has a 12% risk of developing breast cancer during her lifetime. Having a BRCA mutation increases that from 27% up to 72%. BRCA mutations tend to develop in younger women (30s and 40s) and occur more often in both breasts, compared to women without BRCA mutations. Only 1 in 400 people have mutations of the BRCA gene. 

Learn about the risk factors of breast cancer

If you have a family history on either side that matches one or more of the conditions listed above, your doctor may recommend genetic testing. A genetic counselor can help you understand the benefits of genetic testing and its drawbacks. 

Pros of Genetic Testing

  • You can make behavioral changes to match your risk level.
  • You and your doctor may recognize breast cancer sooner.
  • It can have an impact on reproductive/adoption decisions.
  • Your children may want to be tested based on your test results.

Cons of Genetic Testing

  • Knowing may worsen anxiety or depression. It's important to explore your feelings and speak with a counselor in addition to your genetic counselor.
  • Lack of BRCA mutations could give you a false sense of confidence.

If Testing Confirms a BRCA Gene Mutation 

Having a BRCA gene mutation doesn't mean you're definitely going to develop breast cancer. However, knowing will make you and your doctors look more thoroughly at anything abnormal, just to be sure. Here are some next steps to consider:

1. Continue regular breast exams and mammograms. 

Your doctor may recommend starting breast cancer screening at a younger age than normal. Mammograms and other imaging tests, such as an ultrasound or MRI, may be used.

If you have a gene mutation, the National Comprehensive Cancer Network (NCCN) recommends:

  • Continue or start monthly breast self-exams
  • Get a clinical breast exam every 6-12 months, starting at age 25
  • Get 3D mammograms
  • Consider continuing breast cancer screenings after age 75

Related Reading: 

Detecting Breast Cancer Early with 3-D Mammograms

what to expect from a 3d mammogram

2. Consider preventive mastectomy. 

A preventive mastectomy can prevent breast cancer, especially if your risk is very high because of a BRCA gene mutation combined with other risk factors. This is a very personal discussion to have with your oncologist and genetic counselor. As with all surgeries, including breast cancer surgery, there are risks to consider.

3. Make healthier lifestyle choices 

Making healthier lifestyle choices can reduce your risk, such as not smoking. Other lifestyle choices that the NCCN says are linked to a lower risk of developing cancer include:

  • Eat a healthy and varied diet that includes vegetables, fruits, nuts, seeds, and beans.
  • Manage your weight.
  • Meet or exceed CDC guidelines for physical activity, or at least 150 minutes of moderate activity plus strength training every week.

4. Other recommendations

  • Keep alcohol consumption to one or no drinks per day.
  • Choose to breastfeed after giving birth for a year if you can. 
  • Find natural ways to manage post-menopausal side effects to avoid taking hormones.

Where to Begin With Breast Cancer Genetic Testing

If you think you may want or need to be tested for BRCA or other gene mutations, meet with a genetic counselor. Breast cancer specialists will evaluate your personal situation and possible risk factors for breast or ovarian cancer. This area of medicine is changing so fast that even if you've had genetic testing, you may need to be tested again for newly discovered gene mutations. This will help you and your doctor better understand your risk of developing breast cancer. If you are recently diagnosed, genetic testing can also help determine your treatment options for breast cancer.

Genetic information leads to improved cancer prevention

If you have additional questions, our breast cancer specialists answer common questions about breast cancer to help patients know their options and choose the best treatment plan for them.

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