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If your breast cancer has metastasized, or spread, it will be classified based on three receptors, like all invasive cancers are. Several treatments are available, but their effectiveness might vary based on your MBC subtype.

Not all breast cancers are the same. If you’ve already received an MBC diagnosis, your doctor will likely perform additional tests.

This information will help you and your healthcare team select the best treatment option. Certain treatments are more effective in breast cancers with a specific subtype, gene mutation, or other features.

Your doctor will review the results of diagnostic imaging tests, such as bone scans, X-rays, MRIs, PET scans, and CT (CAT) scans, to understand where and how the cancer has metastasized, or spread. These are known as metastases.

Standard MBC testing looks at three key receptors:

  • estrogen receptor (ER)
  • progesterone receptor (PR)
  • human epidermal growth factor receptor-2 (HER2)

They’re proteins in or on the cells that attach to substances in the blood.

Testing positive for ER or PR puts the cancer in a category called hormone receptor-positive (HR-positive). Your doctor may then classify the cancer into one of these subtypes:

  • HR-positive/HER2-negative
  • triple-positive (HR-positive/HER2-positive)

HR-positive or negative

Hormone receptors include the estrogen and progesterone receptors. These proteins allow hormones like estrogen and progesterone to “feed” the cancer cells.

Hormone receptor status is either positive or negative. You may test positive for ER, PR, or both to be considered HR-positive.

According to Breastcancer.org, about 80% of breast cancers test positive for ER. Of those, about 65% are also PR-positive.

HER2-positive or negative

HER2 is a protein involved in cell growth found on the outside of all breast cells. Breast tumors with higher-than-expected levels of this protein are referred to as HER2-positive tumors.

Triple-negative

Triple-negative breast cancer means that the tumor is negative for HER2, ER, and PR.

About 10 to 15% of breast cancers are triple-negative, according to the American Cancer Society.

Triple-positive

With triple-positive breast cancer, the tumor is positive for HER2, ER, and PR.

In a 2019 study of 1,205 people with breast cancer, roughly 10% had triple-positive breast cancer.

Your doctor may recommend lab tests on a tumor sample to identify unique factors, such as gene mutations and proteins.

They may then use this information to help select a treatment. Some drugs work best when these proteins or gene mutations are present.

PD-1 and PD-L1

PD-1 (programmed cell death protein 1) is a T cell (immune cell) protein that prevents the immune system from activating excessively when bound to another protein called PD-L1 (programmed death-ligand 1).

PD-L1 may be found on breast cancer cells and some of the body’s immune cells. This protein keeps immune cells from destroying the cancer.

If you have this receptor and triple-negative breast cancer, adding immunotherapy drugs to standard chemotherapy may improve your outcome.

PIK3CA gene mutations

PIK3CA mutations are found in up to 40% of HR-positive, HER2-negative breast cancers.

Your doctor may prescribe drugs targeting the PIK3CA gene if a PIK3CA mutation is found.

BRCA1 or 2 gene mutations

The BRCA1 and BRCA2genes are involved in DNA repair. Mutations in these genes are related to an increased risk of breast cancer.

Tumors with mutations in either gene may respond to a newer class of drugs called PARP inhibitors. These drugs inhibit cancer cells from repairing their damaged DNA alone or when combined with chemotherapy.

Once you’ve received information about your cancer’s HER2 and HR status and other genetic features of the tumor, your doctor will use this information to inform treatment decisions.

Treatment options will depend on your tumor subtype. Your doctor will create a plan, but you’ll ultimately decide which treatment you receive.

Writing notes before your appointment can help you remember talking points. You may want to also come prepared with a few questions, such as:

  • What are the possible side effects of treatment?
  • How will the treatment affect my quality of life?
  • What other treatment options are available, and what are the advantages and disadvantages of each?
  • What happens if I delay treatment?
  • Are clinical trials available or upcoming new medications that may be an option for my tumor type?

While MBC doesn’t currently have a cure, treatments to manage symptoms and keep the cancer from spreading further are available:

  • Hormone therapy: Anti-estrogen therapy, such as tamoxifen, fulvestrant (Faslodex), or aromatase inhibitors, are recommended to treat HR-positive cancers. Hormone therapy helps from feeding cancer cell growth.
  • Chemotherapy: Your doctor may recommend chemotherapy, especially if your tumor is triple-negative and won’t respond to hormone therapies.
  • Targeted therapy: This therapy targets cell changes that cause abnormal cell growth. Targeted therapies, such as trastuzumab or pertuzumab, may be used together with chemotherapy for HER2-positive breast cancer. Targeted therapies can also be used with hormone therapy or to target BRCA gene mutations.
  • Radiation: This therapy can shrink tumors that have spread to other body parts. It’s typically used to help decrease pain and other symptoms.
  • Surgery: If the cancer has already spread, surgery may not remove all of the cancer.
  • Immunotherapy: This involves treatments to stimulate a person’s immune system to recognize and destroy cancer cells more effectively. New immunotherapies that target PD1/PD-L1, such as pembrolizumab (Keytruda), have been shown to successfully treat triple-negative MBC.

It’s important to discuss with your doctor the expected side effects of any treatments.

The results of laboratory and genetic testing for MBC are used to determine the best options for treating your cancer. Treatment can depend on where exactly the cancer has spread.

The use of more targeted therapies has greatly improved the outlook for MBC.

Once you understand your subtype, you can talk with your doctor about which treatment or combination treatments will likely be the most effective.

Remember to discuss the possible side effects of any treatments you seek. Treatments won’t cure MBC, but they can help improve your quality of life.