and Genetic Testing for People with Breast Cancer
This section covers the following topics:
- Tumor testing for treatment selection
- tests for prognosis in breast cancer
- Genetic testing for inherited mutations
tests look at samples of blood, tumor or other tissue for changes or abnormalities caused by cancer. These tests can give doctors clues about the cancer, including:
- how fast the cancer is growing
- which treatments are most likely to work
- whether or not the cancer is responding to treatment or growing
- whether or not the cancer has come back after remission
tests may be used to select treatments, and help patients avoid side effects from treatments that will not work for them. tests used to select a specific treatment are sometimes called "companion diagnostic tests." These tests may be done on tumor tissue or (in many cases) on blood. See our Testing section for more information.
receptors (ER), progesterone receptors (PR) and
After breast cancer tissue is removed by surgery or biopsy, all breast cancers are tested for three common biomarkers:
- Hormone receptors: Testing is done to look for two separate hormone receptors, receptors (ER) and progesterone receptors (PR).
- Cancers that test positive for and progesterone receptors are known as . They may also be called . These cancers are often treated with hormone therapies.
- Cancers that test negative for and progesterone receptors are known as or HR-negative. These cancers are not usually treated with hormone therapy.
- is a protein that is found on all breast cancer cells. Tests measure the amount of protein in the tumor and provide a score from 0 to 3+.
- Cancers with a score of 3+ are considered . These cancers are often treated with drugs called "anti-HER2 agents."
- Cancers with a score of 1+ or 2+ are considered HER2-low. This is a relatively new label for breast cancer. In the past, these cancers would have been called or borderline. Advanced HER2-low breast cancers may be treated with the anti-HER2 agent Enhertu (T-DXd).
- Cancers with a score of 0 are called . These cancers are not treated with anti-HER2 agents.
Other biomarkers used for breast cancer treatment selection
Additional testing may be done to study the genes and proteins within the cancer to help doctors choose the best treatment. Some treatments will work best for people whose cancer cells have specific changes. These treatments are sometimes called targeted therapies. The for a specific is sometimes called a . Some tests look for only one at a time, while others may test for all many biomarkers at the same time. Panel tests look for multiple markers, including FDA-approved treatments as well as those that have not yet been proven effective in breast cancer. Examples of multiple tumor tests for breast cancer include:
- Tempus xT
Examples of biomarkers used to guide breast cancer treatment include:
- ESR1 mutation testing in advanced breast cancer for treatment with the drug Oserdu (olacestrant).
- PIK3CA mutation testing in ER-positive, advanced breast cancer for treatment with the drug PIQRAY (alpelisib).
- , PIK3 or AKT1 mutation testing in , advanced breast cancer for treatment with the Truqap (capivasertib).
- PD-L1: Testing for the protein can help find people with advanced () who are most likely to respond to the drug Keytruda (pembrolizumab).
- Additional tumor testing may help people learn if they are eligible for certain clinical trials.
These tests are used for people with ER/PR-positive cancers to predict:
- if the cancer is likely to come back
- the benefit of adding chemotherapy to the treatment plan
- how long hormonal therapy should be used
Some examples of the most commonly used prognostic tests for breast cancer are listed below:
- Oncotype Dx
- Breast Cancer Index
Genetic testing for an may be used to guide treatment selection for people diagnosed with breast cancer.
- People with advanced breast cancer who test positive for an inherited or mutation may benefit from treatments known as PARP inhibitors. Two PARP inhibitors—Lynparza and —are approved as for treating advanced breast cancer in people with a or mutation.
- Lynparza may be used to as after treatment for people with an inherited or mutation who have breast cancer this is high risk for recurrence.
- People who test positive for other inherited gene mutations may qualify for clinical trials looking at targeted therapies to treat hereditary breast cancer.
The National Comprehensive Cancer Network has guidelines on who should undergo genetic counseling and testing. If you have been diagnosed with breast cancer, you should speak with a genetics expert about genetic testing if any of the following apply to you:
- You have a blood relative who has tested positive for an
- You have any of the following:
- Breast cancer at age 50 or younger
- Male breast cancer at any age
- Ovarian cancer at any age
- at any age
- Two separate breast cancer diagnoses
- Eastern European Jewish ancestry and breast cancer at any age
- Lobular breast cancer and a family history of diffuse gastric cancer
- For treatment decisions for people with breast cancer or people with early , breast cancer who are at high-risk for recurrence
- Testing of your tumor shows a mutation in a gene that is associated with
- You have one or more close family members who have had:
- Young-onset or rare cancers
- Breast cancer at age 50 or younger
- Male breast cancer, ovarian cancer, pancreatic cancer, or cancer at any age
- Two separate cancer diagnoses
- prostate cancer or cancer that is high-risk or very-high-risk group.
The American Society of Breast Cancer Surgeons (ASBrS) released guidelines in 2019 that recommend all women diagnosed with breast cancer have access to genetic testing for inherited mutations in breast cancer genes.
If you are uncertain whether you meet the guidelines above and you are interested in or considering genetic testing, you should speak with a cancer genetics expert.