Genetics and family risk

After being diagnosed with breast cancer, you may wonder “Why me?” or “What caused this?” These are common questions that, for many women, go unanswered.

According to the National Cancer Institute, 1 in 8 American women will develop breast cancer in her lifetime. Certain genes, small pieces of your DNA, can cause breast cancer to grow when they have a mutation, or error.

Hereditary and non-hereditary mutations

Most breast cancers are caused by somatic mutations. These are not passed on to you from your parents and can’t be passed on to your children, meaning they are not hereditary. Somatic mutations form on their own in breast cells during your lifetime and what triggers them is not always known. Breast cancers caused by somatic mutations are not hereditary breast cancers.

A small group of women will be diagnosed each year with breast cancer considered to be hereditary. Mutations that cause hereditary cancer may be passed on to you from your parents in the same way as traits like height or eye color.

These are some important points to remember about genetic mutations and breast cancer:

• Having breast cancer does not mean you have an inherited mutation
• If you are not already diagnosed, having a hereditary gene mutation does not mean that you will definitely get breast cancer
  • These gene mutations only put you at greater risk of developing breast cancer than people who don’t carry them
• Most women with breast cancer do not have inherited gene mutations
• Men who have been diagnosed with breast cancer are more likely to have a mutation

NOTE: Throughout this section, “gene mutation” is used to mean “hereditary gene mutation,” for which testing is available.

Gene mutations and increased risk

Researchers have identified some mutations associated with increased risk for breast cancer, located on different genes that exist in every human body. Some of these mutations, like BRCA1 and BRCA2, increase your risk significantly, while others increase it only slightly.

A genetic counselor will be able to tell you which mutations you test positive for. He or she can also suggest whether to take any medical action to help lower your risk of developing breast or ovarian cancer. Not all mutations will require preventive measures like surgery or risk-reducing medicine.

Genes related to breast cancer

Researchers know of several inherited gene mutations that increase the risk of breast and ovarian cancer. Some are more likely than others to lead to cancer. You may have heard of mutations to BRCA1 and BRCA2, the two genes most commonly linked to hereditary breast cancer. Only a small percentage of all breast cancers are thought to be caused by BRCA mutations.

BRCA1 and BRCA2

BRCA1 and BRCA2 are the genes most commonly linked to hereditary breast cancer. They are also related to ovarian cancer. BRCA mutations are passed to you from your mother or father, at birth. If either of your parents has a mutation, you have a 50 percent chance of having it, too. In the United States, about 1 in 500 women have either a BRCA1 or BRCA2 mutation, though in some groups of people, that risk may be higher. For example, if you come from an Ashkenazi Jewish background (your family is Jewish and comes from Eastern or Central Europe), your risk is around 1 in 40.

Women with a BRCA mutation have a higher risk of developing breast cancer over the course of their lifetime. The risk of developing breast cancer for a woman without a mutation is about 12 percent. If you carry a BRCA1 mutation, that risk rises to 72 percent. If you carry a BRCA2 mutation, that risk is about 69 percent.

If you have not been diagnosed with breast cancer, having a higher risk because you have a BRCA mutation does not mean you will definitely get breast cancer. And, there are steps you can take to try and prevent the disease, make it less likely to develop, or have it diagnosed earlier:

• get cancer screenings earlier and more often
• have prophylactic, or preventive, surgeries like mastectomy or oophorectomy
• take certain medicines known to help with risk

If you have already been diagnosed with breast cancer and have a BRCA mutation, research shows your risk of recurrence is the same as a person who does not have a mutation. But you do have a higher risk of developing a second primary breast cancer, a breast cancer that is not related to your first diagnosis.

If you’re worried about BRCA gene mutations because of a known mutation in your family or a strong family history of the disease, you can talk to your doctors about your concerns and ask for information on genetic testing.

Other gene mutations

BRCA1 and BRCA2 are not the only genes linked to an increased risk of breast cancer. Some other genes we know are related to breast cancer risk are

• ATM
• BARD1
• CDH1
• CHEK2
• PALB2
• PTEN
• STK11
• TP53

For most of these genes, researchers don’t quite know by how much mutations impact the risk of developing breast cancer. Some of these genes, like CHEK2 and ATM, have a relatively modest effect on breast cancer risk, about the same as having a sister diagnosed with breast cancer at a young age. But studies show that women who have a mutation in one, PALB2, may have a 33 to 58 percent chance of getting breast cancer by age 70, or about 7 times more likely than women with no breast cancer-related gene mutations. Genes like CDH1, PTEN, STK11, and TP53 can cause increased risks of other kinds of cancers in a family.

A genetic counselor can help you understand whether your family history may increase the chance that you may have one of these gene mutations. Researchers continue to explore other genes that may be related to breast cancer risk.

Interactive Questionnaire: https://www.hereditarycancerquiz.com/mgl