Genetics and Family Risk

August 31, 2015
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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 mutationinfo-icon , or error.


Hereditary and Non-Hereditary Mutations

Most breast cancers are caused by somaticinfo-icon mutations. These are not passed on to you from your parents and can’t be passed on to your children, meaning they are not hereditaryinfo-icon. Somatic mutations form on their own 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 that traits like height or eye color are.

These are some important points to remember about geneticinfo-icon mutations and breast cancer:

  • Having breast cancer does not mean you have an inheritedinfo-icon mutationinfo-icon
  • If you are not already diagnosed, having a hereditary geneinfo-icon 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 BRCA1info-icon and BRCA2info-icon, 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 cancerinfo-icon. Not all mutations will require preventiveinfo-icon measures like surgeryinfo-icon or risk-reducing medicineinfo-icon.

Genes Related to Breast Cancer

Researchers know of several inheritedinfo-icon geneinfo-icon mutations that increase the risk of breast and ovarian cancerinfo-icon. Some are more likely than others to lead to cancer. You may have heard of mutations to BRCA1info-icon and BRCA2info-icon, the two genes most commonly linked to hereditaryinfo-icon breast cancer. Only a small percentage of all breast cancers are thought to be caused by BRCA mutations.

Some other genes we know are related to breast cancer risk are

  • ATM
  • 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. But recent studies showed that women who have a mutationinfo-icon in one, PALB2, may have a 33 to 58 percent chance of getting breast cancer by age 70. Women who have BRCA mutations have a 45 to 85 percent chance. Women with no mutations have about a 12 percent chance of developing breast cancer over the course of their lifetime.

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