Genetic Testing Before and After a Breast Cancer Diagnosis

Healthcare professionals conduct genetic testing to learn whether someone has genetic changes that may affect their health. This is done through a blood test or a saliva test. These changes are known as genetic mutations.

Genes are segments of DNA inside each cell of your body. They provide instructions for making proteins that control your body’s functions.

Genetic mutations can change how your body produces proteins, which may lead to cancer or other conditions.

Your doctor may order tumor genetic testing, germline genetic testing, or both.

Tumor genetic testing

Tumor genetic testing looks for genetic changes in tumor cells.

Genetic mutations can occur during cell division. These mutations may cause cells to multiply faster than normal leading to cancer. Certain mutations may affect how the cancer develops and responds to treatment.

Your doctor will recommend tumor genetic testing if you receive a diagnosis of breast cancer.

Germline genetic testing

Germline genetic testing checks whether someone has inherited genetic mutations that raise their risk of breast cancer or another condition.

Guidelines from the National Comprehensive Cancer Network (NCCN) recommend germline genetic testing if you have a biological relative who has tested positive for a genetic mutation that increases breast cancer risk, such as a BRCA 1 or BRCA 2 mutation.

The NCCN guidelines also recommend germline genetic testing for some but not all people who receive a diagnosis of breast cancer or have a close biological relative with breast cancer or another related type of cancer.

Talk with your doctor to learn whether germline genetic testing may be suitable for you.

Your doctor will consider your personal and family medical history when assessing your risk of germline genetic mutations. They may also refer you to a genetic counselor for more information and support.

There are no genetic tests for diagnosing metastatic breast cancer, but certain genetic tests may help your doctor assess your risk of developing it. Genetic testing may also help them predict which treatments will work best.

Testing for tumor gene mutations

If you receive a diagnosis of breast cancer, your doctor will likely order tumor genetic testing for mutations in the human epidermal growth factor receptor 2 (HER2) gene.

The HER2 gene gives your body instructions for producing HER2 receptors on breast cells. When HER2 receptors are turned on, they tell breast cells to grow and divide. Mutations in the HER2 gene can lead to too many HER2 receptors on breast cells, causing them to grow uncontrollably and form tumors.

Breast cancers that test positive for ­HER2 mutations are called HER2-positive breast cancers. They grow faster and are more likely to spread than HER2-negative breast cancers.

Your doctor may also test for mutations in other tumor genes, such as the:

• PIK3CA gene mutation
• ESR1 gene mutation
• NTRK fusion gene mutations
• mismatch repair gene mutations

They’ll also order tests to learn whether the tumor cells have estrogen or progesterone receptors that will cause the cancer to grow in response to those hormones.

Testing for tumor gene mutations and hormone receptors can help your doctor predict how the breast cancer will respond to certain treatments.

Testing for inherited mutations

Depending on your personal and family medical history, your doctor may order germline genetic testing for mutations in the BRCA1 and BRCA2 genes.

The BRCA1 and BRCA2 genes give your body instructions for producing tumor suppressor proteins. When these genes are normal they help prevent cancer cells from growing. Mutations in these genes can trigger excess cell growth and raise your risk of breast cancer, as well as ovarian cancer and some other types of cancer.

Breast cancer may also be more likely to spread or recur in people with BRCA1 or BRCA2 mutations.

Your doctor may also test for germline mutations in other genes that may affect your breast cancer risk, such as:

• CDH1 gene mutations
• PALB2 gene mutations
• PTEN gene mutations
• TP53 gene mutations

Testing for germline mutations can help your doctor assess your risk of developing breast cancer or experiencing a breast cancer recurrence. It may also provide clues about your family members’ potential risk of breast cancer.

Germline genetic testing may also help your doctor predict how well certain cancer treatments will work.

Tumor genetic testing and germline genetic testing involve different procedures.

Tumor genetic testing

Your doctor will collect a sample of tumor tissue to test for HER2 and other tumor gene mutations. This procedure is known as a breast biopsy.

They will conduct one of the following types of biopsy:

• fine needle aspiration biopsy, which uses a very thin needle to remove cells and fluid
• core needle biopsy, which uses a larger, hollow needle to remove a sample of breast tissue
• surgical biopsy, which makes a small cut in the breast during a surgical procedure to remove a piece of tissue

Your doctor will send the tissue sample to a laboratory for testing.

Germline genetic testing

Your doctor may order a blood test or saliva test to check for germline genetic mutations.

A healthcare professional will insert a needle into a vein in your arm to collect a sample of blood for testing.

Alternatively, they may use a soft cotton swab to collect a sample of saliva from inside your cheek for testing.

They will send the sample to a laboratory for testing.

You and your doctor will receive a copy of the genetic test results when they become available.

If a genetic test result is positive, that indicates that you or the tumor has the genetic mutation.

If a genetic test result is negative, that indicates that you or the tumor does not have the genetic mutation.

Sometimes test results are borderline, which means your doctor may not know whether or not you have the mutation. It is also possible for false positive or false negative results to occur.

Your doctor can help you understand and interpret your test results during a follow-up appointment.

They may also refer you to a genetic counselor for more information and support.

Certain genetic mutations affect how breast cancer develops and responds to certain treatments. Your doctor may use genetic test results to guide your treatment plan for early or metastatic breast cancer.

Treating early breast cancer

Early breast cancer is breast cancer that has not yet spread from the breast to distant organs.

Your doctor will likely prescribe one or more of the following treatments for early breast cancer:

• surgery
• radiation therapy
• hormone therapy
• chemotherapy drugs
• targeted therapy drugs
• immunotherapy drugs

Surgery is sometimes enough to treat early breast cancer, but you may need surgery in combination with other treatments. Additional treatments can help shrink the tumor before surgery, kill any cancer cells that may remain after surgery, and reduce the risk of the cancer returning.

If you test positive for BRCA mutations, your doctor may recommend a bilateral mastectomy to remove both breasts. This reduces the chances of breast cancer returning.

If your breast cancer is HER2-positive, your treatment will likely include:

• surgery, with or without radiation therapy
• chemotherapy before surgery
• HER2-targeted therapy

Multiple HER2-targeted therapies are available, including:

• trastuzumab (Herceptin)
• pertuzumab (Perjeta)
• ado-trastuzumab emtansine (Kadcyla)
• neratinib (Nerlynx)

Doctors usually start by prescribing Herceptin, with or without Perjeta. If those HER2-targeted therapies are not effective, they may prescribe Kadcyla or Nerlynx.

If your breast cancer is hormone-receptor-positive, your doctor will likely prescribe hormone therapy in combination with other treatments.

Treating metastatic breast cancer

Metastatic breast cancer has spread from the breast to distant organs. There is currently no cure for metastatic breast cancer, but treatment may help people with this condition live for longer and with higher quality of life.

Your doctor will likely prescribe one or more of the following treatments for metastatic breast cancer:

• hormone therapy
• chemotherapy drugs
• targeted therapy drugs
• immunotherapy drugs

If you test positive for BRCA1 or BRCA2 mutations, your doctor may prescribe a type of targeted therapy known as a PARP inhibitor. These include the medications olaparib (Lynparza) and talazoparib (Talzenna).

If your breast cancer is HER2-positive, your treatment will likely include chemotherapy in combination with the HER2-targeted therapies Herceptin and Perjeta. Your doctor may also prescribe other HER2-targeted therapies.

If your breast cancer is PIK3CA-positive, your doctor may prescribe a type of targeted therapy known as a PIK3 inhibitor. This includes the medication alpelisib (Piqray).

If your breast cancer is hormone-receptor-positive, your doctor will likely prescribe hormone therapy in combination with other treatments.

In some cases, your doctor may also prescribe radiation therapy. This treatment tends to be less effective for treating metastatic breast cancer but may help relieve certain symptoms.

Preventive treatment

Some people receive genetic testing for BRCA or other genetic mutations after a family member tests positive for the mutation or receives a diagnosis of breast cancer or another related type of cancer.

If you receive a BRCA-positive test result, your risk of developing breast cancer is increased. BRCA mutations may also increase the risk of some other types of cancer, such as ovarian cancer.

Your doctor can help you learn how to manage your increased cancer risk.

They may recommend earlier or more frequent mammograms to screen for breast cancer.

Some people also choose to receive risk-reducing surgery, such as:

• prophylactic bilateral mastectomy, which removes both breasts
• prophylactic salpingo-oophorectomy, which removes the ovaries and fallopian tubes

These surgeries reduce the risk of breast cancer or ovarian cancer developing, but they do not remove the risk entirely. They also carry a risk of serious and long-term side effects.

Your doctor or genetic counselor can help you understand the potential benefits and risks of risk-reducing surgery.

Your doctor may refer you to a genetic counselor if you’re thinking about getting germline genetic testing for BRCA mutations or other germline mutations that affect cancer risk.

They may also encourage you to speak with a genetic counselor if a close biological family member tests positive for a germline genetic mutation or receives a diagnosis of cancer that might be linked to a germline mutation.

A genetic counselor can help you learn about:

• your risk of carrying or passing on a germline genetic mutation
• the potential benefits and risks of germline genetic testing
• the implications of germline genetic test results
• strategies to manage genetic cancer risk

A genetic counselor can also help you learn whether other family members benefit from genetic counseling or genetic testing. Germline mutations are inheritable, which means they run in families.

You can speak with your doctor to learn whether genetic counseling may be appropriate for you. They may refer you to a genetic counselor or share tips for finding one.

You can visit the National Society of Genetic Counselors Website to search for a genetic counselor near you.

Talk with your doctor about genetic testing if you’ve received a diagnosis of breast cancer. They may recommend tumor genetic testing, germline genetic testing, or both. The test results may help guide your treatment plan.

Your doctor may also recommend germline genetic testing if a close biological relative tests positive for a genetic mutation that raises breast cancer risk or receives a diagnosis of breast cancer or another related type of cancer.

Your doctor can help you learn more about the potential benefits and risks of genetic testing.

They may also refer you to a genetic counselor for support.