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Targeted therapy for hormone-receptor positive breast cancer


Hormone-receptor positive breast cancers grow in response to the hormones estrogen and progesterone. These cancers are often treated with hormonal therapy medicines.

Hormonal therapy medicines can work in two ways. They either stop the body from making estrogen or they block the effects of estrogen that drive cancer growth.

Over time, some breast cancers build resistance to hormonal therapies. If this happens, your doctor may then suggest a different medicine. The new medicine might be a targeted therapy. Studies have shown that some hormonal therapies are more effective when combined with certain targeted therapies.

Targeted therapies are treatments that target specific proteins or markers on or within cancer cells that help cancer cells grow. There are many different kinds of targeted therapy. Hormonal therapy is a type of targeted therapy because it targets hormones that are active in cancer growth. Hormonal therapy has been used to treat breast cancer for many years. Doctors now use other new kinds of targeted therapy to treat hormone receptor-positive breast cancer as well.

The FDA has approved three kinds of targeted therapy to treat hormone receptor-positive breast cancer –  CDK 4/6 inhibitors, mTOR inhibitors, and PI3K inhibitors. These medicines are mostly used to treat metastatic breast cancers. Only one CDK 4/6 inhibitor is also approved for early-stage breast cancer.

If you have hormone receptor-positive breast cancer and are interested in targeted therapies, ask your doctor whether these medicines are an option for you. If they are not, ask if you might be able to participate in a clinical trial.

In this section, you’ll learn more about the classes of targeted therapies used to treat hormone receptor-positive breast cancer and the medicines within each type.

Targeted therapies often have fewer side effects than chemotherapy, but like any medicine, they may still cause them. Medicines that target features of cancer cells that are also in healthy cells can cause more side effects. Side effects vary in type and level of seriousness. What you experience depends on how your body responds to the medicine.

Your doctor, pharmacist, or nurse can help you manage any side effects. Visit our Side Effects page for more information on common side effects and how to cope with them.

CDK 4/6 inhibitors

CDK 4/6 inhibitors, also called cyclin-dependent kinase 4/6 inhibitors, target two specific kinases, CDK 4 and 6. These kinases, or proteins, signal cancer cells to grow and divide. This type of medicine slows the growth or spread of cancer cells. Three CDK 4/6 inhibitors are approved to treat metastatic breast cancer. Of the three, only abemaciclib is also approved for early-stage breast cancer. The three CDK 4/6 inhibitors are:

mTOR inhibitors

mTOR, or mammalian target of rapamycin, is a type of protein called a kinase. Kinase helps control cell growth.

In some cancers, mTOR-activated proteins work abnormally and encourage cancer cells to grow and spread. mTOR also directs nutrients to the cancer cells, helping to support them.

mTOR inhibitors are a newer type of targeted therapy. They work to slow or stop mTOR’s role in the growth of cancer cells. The mTOR inhibitor approved to treat metastatic breast cancer is:

PI3K inhibitors

PI3K, also called phosphatidylinositol-3 kinase, is a family of enzymes that sends signals that affect cell growth. One medicine of this kind is approved to treat hormone receptor-positive, HER2-negative metastatic breast cancer that has a specific mutation, PIK3CA, in postmenopausal women and in men:


Reviewed and updated: July 25, 2022

Reviewed by: Tiffany Avery MD MPH


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