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Genetic Testing for Breast Cancer: Your Guide

Medically reviewed by Mark Levin, M.D.
Written by Maureen McNulty
Posted on June 14, 2022

If you are at risk for breast cancer, your doctor may recommend genetic testing. Usually, genetic testing for breast cancer refers to tests that look for gene mutations that raise a person’s risk of developing this condition.

Doctors may suggest genetic testing for certain women who have breast cancer or have risk factors that increase the likelihood that they will develop breast cancer in the future.

For women who have already been diagnosed with breast cancer, doctors may also recommend tests to identify gene changes that influence how cancer cells grow. This is also sometimes referred to as genetic testing, or it can be called molecular profiling or next-generation testing. Knowing this information can help doctors estimate your prognosis (outlook) and choose treatments that are most likely to be effective.

What Is Genetic Testing for Cancer?

Cancer is caused by gene mutations (gene changes). Genes tell cells how to make proteins, which play many roles in the cell. When genes are mutated, they cause the cell to make abnormal proteins that lead the cell to grow out of control, resist death, or accumulate damage.

Occasionally, cancer is caused by inherited gene mutations — changes that are passed down from parent to child, and are present in all of a person’s cells at birth. More often, cancer is caused by acquired gene mutations, which develop in one cell during a person’s lifetime.

Genetic testing usually looks for inherited gene mutations, and some tests also look for acquired mutations. These tests “read” the DNA sequence within cells to determine whether there are any changes within genes that can cause cancer.

This type of genetic testing is different from at-home DNA tests that provide information about personal traits and ancestry. The at-home tests can detect only a few cancer-causing genetic mutations.

There are more than 1,000 inherited gene changes that can cause breast cancer. Many people have high-risk gene changes that won’t be detected using these tests. Additionally, these at-home tests are not usually covered by health insurance, whereas genetic testing through a doctor may be covered.

Types of Genetic Testing

Most types of genetic testing for breast cancer help women understand whether they have inherited gene changes that can lead to cancer. In some cases, genetic tests can be used to help determine what type of breast cancer a woman has.

BRCA Gene Testing

The most common type of genetic testing in people with breast cancer includes tests that look for changes in the BRCA1 and BRCA2 genes. Mutations in these genes lead to hereditary breast and ovarian cancer syndrome. People with BRCA gene mutations are more likely to develop breast and ovarian cancer, as well as other types of cancer such as pancreatic cancer, prostate cancer, and melanoma.

Who Needs BRCA Gene Testing?

Doctors may recommend BRCA gene testing for women with a personal or family health history that shows they may be at risk. Those at risk include women who have been diagnosed with:

  • Breast cancer before turning 45 years old, or with both breast and ovarian cancer at any age
  • Breast cancer in both breasts, or twice in the same breast
  • Triple-negative breast cancer before the age of 60
  • A personal history of ovarian cancer
  • Breast cancer and who are of Ashkenazi Jewish descent

Those also at risk include:

  • Men who have been diagnosed with breast cancer
  • People who have developed multiple types of cancer
  • People who have a family history of breast cancer, ovarian cancer, fallopian tube cancer, prostate cancer, or pancreatic cancer
  • People who have close relatives who are known to have a BRCA mutation

Doctors may also use different tools to help estimate a person’s risk of breast cancer. These tools show if a person is more or less likely to have a BRCA mutation and can help doctors decide whether to recommend genetic testing.

How Is BRCA Gene Testing Performed?

BRCA gene testing begins with genetic counseling. The counselor will help you understand the genetic testing process.

They will ask about your personal and family medical history. It may help to bring any relevant medical records that you have for yourself, as well as information about which of your relatives have had cancer, the age they were diagnosed, and which type of cancer they had.

During the genetic counseling meeting, you can also ask the counselor questions about genetic testing, including what the risks and benefits are and what the possible results may mean.

Usually, BRCA gene testing requires a blood sample. A health care provider will draw blood from your arm and send it to a lab for testing. Occasionally, gene testing may be performed with a saliva test or from a cheek swab.

Once the tests are complete, a person undergoing testing will have another meeting with the genetic counselor. The counselor will share the test results and explain what they mean.

What Does BRCA Gene Testing Tell You?

A positive test result means that you have an inherited BRCA gene mutation that leads to an increased risk of developing cancer. If you have not yet developed cancer, preventive treatments may help lower your risk.

Additionally, you may need to undergo breast cancer screening earlier and more often than women within the general population. You may also be at risk for developing other types of cancer. Your family members may want to be tested to see whether they also have this inherited mutation.

If you have already been diagnosed with breast cancer, testing positive for BRCA can provide information about which cancer treatments may be most effective. BRCA-positive breast cancers can be treated with PARP inhibitor drugs, including olaparib (Lynparza) and talazoparib (Talzenna).

A negative test result indicates that genetic testing did not find any inherited BRCA gene changes known to increase cancer risk. This does not guarantee that you won’t develop breast cancer. It may mean that you have an average risk of being diagnosed with breast cancer. It is also possible that you have an inherited mutation in a different gene other than BRCA1 or BRCA2 that raises your risk of breast cancer.

Sometimes, genetic testing results say that you have a variant of uncertain significance. This means that you have a BRCA1 or BRCA2 mutation, but experts don’t yet know whether this particular gene change increases breast cancer risk. Talk to your genetic counselor to learn more about what this result may mean for you.

Genetic Testing for Other Inherited Gene Mutations

Some people inherit mutations that affect other genes besides the BRCA genes. Mutations that can raise cancer risk include changes in the following genes:

  • TP53
  • PTEN
  • PALB2
  • ATM
  • CHEK2
  • BARD1
  • NF1
  • STK11

Many genetic tests look for mutations in these genes as well as in BRCA genes. This type of testing may be called multigene testing or expanded panel testing. These tests work similarly to BRCA gene testing.

Human Epidermal Growth Factor Receptor 2 Testing

Human epidermal growth factor receptor 2 (HER2) testing can help doctors diagnose breast cancer’s molecular subtype. It is not a genetic test. Doctors classify breast cancer cells based on which genes or proteins they contain. Identifying the molecular subtype helps doctors estimate outlook and know which treatments may work best.

When analyzing the molecular subtype, doctors look at whether breast cancer cells contain the proteins HER2, estrogen receptor (ER), and progesterone receptor (PR). Some HER2 testing relies on genetic tests. ER and PR testing is accomplished through other methods.

The HER2 gene makes a protein, also called HER2, that helps cells grow. Normal breast cells contain low levels of HER2. For about 1 out of 5 people with breast cancer, the cancerous breast cells have changes in the HER2 gene.

The changes cause the cell to make too much HER2 protein, which makes the cells grow too fast. People with high levels of HER2 in their breast cancer cells are said to have HER2-positive breast cancer.

Who Needs HER2 Testing?

Generally, all women with invasive breast cancer will undergo HER2 tests. They will also be tested for ER and PR.

How Is HER2 Testing Performed?

During HER2 testing, doctors remove a sample of breast cancer cells through various procedures:

  • Fine-needle aspiration biopsy — A tiny breast tissue sample is removed with a thin needle.
  • Core needle biopsy — Breast tissue is removed with a slightly larger needle.
  • Surgical biopsy — Doctors take out a breast lump during surgery.

Once the breast tissue is removed, it is sent to a lab for testing. There are two ways to look at HER2 levels. Immunohistochemistry measures levels of the HER2 protein. Fluorescence in situ hybridization (abbreviated as FISH) is a test that measures levels of the HER2 gene.

What Does HER2 Testing Tell You?

Whether breast cancer is HER2-positive or -negative influences the treatments that a person receives. If you have HER2-positive cancer, you may undergo targeted therapies that block the HER2 protein. These treatments won’t work for someone with low levels of HER2 in their cancer cells. Drug options include:

  • Trastuzumab (Herceptin)
  • Trastuzumab and hyaluronidase injection (Herceptin Hylecta)
  • Pertuzumab (Perjeta)
  • Trastuzumab/pertuzumab/hyaluronidase (Phesgo)
  • Margetuximab (Margenza)
  • Ado-trastuzumab emtansine (Kadcyla)
  • Fam-trastuzumab deruxtecan (Enhertu)
  • Neratinib (Nerlynx)
  • Tucatinib (Tukysa)
  • Lapatinib (Tykerb)

People undergoing treatment for HER2-positive cancer may need to undergo further HER2 testing to find out whether treatments are working. If the treatment plan is successful at killing the cancer cells, testing may show low levels of HER2. On the other hand, if a test shows that there are high levels of HER2 after treatment, it may mean that the treatment isn’t effective or that cancer has returned.

Treatments for HER2-positive breast cancer often work well. As a result, women with HER2-positive breast cancer often have a favorable prognosis compared to those with other molecular subtypes.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, more than 56,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Has your doctor suggested genetic testing for breast cancer? Share your experiences in the comments below, or start a conversation by posting on your Activities page.

Posted on June 14, 2022
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Mark Levin, M.D. is a hematology and oncology specialist with over 37 years of experience in internal medicine. Review provided by VeriMed Healthcare Network. Learn more about him here.
Maureen McNulty studied molecular genetics and English at Ohio State University. Learn more about her here.

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