Targeted therapies are so named because they target certain features of cancer cells that fuel growth. Different kinds of breast cancer use different kinds of fuel. The targeted therapy that’s most likely to be effective depends on the cancer’s characteristics, such as gene alterations and proteins. That’s why targeted therapy is also called personalized or precision medicine.

This article answers some frequently asked questions about targeted therapy for breast cancer.

Targeted therapies aim to work by attacking cancer cells and leaving healthy cells alone. They can only work if cancer cells have particular proteins or genes.

Your doctor can get this information from a biopsy, which can detect targets such as hormone receptors (HR). This includes estrogen receptors (ER) and progesterone receptors (PR). The biopsy also shows whether the cancer is positive for overproduction of a protein called human epidermal growth factor receptor 2 (HER2).

Blood tests can also reveal whether you carry certain biomarkers, such as BRCA gene mutations.

Hormone therapies for HR-positive breast cancers

According to the American Cancer Society, about 3 out of 4 cases of breast cancer are HR-positive. The cancer cells may have receptors for either estrogen or progesterone, which help cancer grow and spread.

Hormone therapies are often used to treat HR-positive breast cancer. These may include:

  • Selective estrogen receptor modulators (SERMs), such as tamoxifen, block estrogen from connecting with cancer cells.
  • Selective estrogen receptor degraders (SERDs), such as fulvestrant and elacestrant, bind to estrogen receptors and cause them to break down.
  • Aromatase inhibitors, such as letrozole, anastrozole, and exemestane, lower estrogen production in the body.

Targeted therapies for HR-positive breast cancers

When used in combination, some targeted therapies may make hormone therapies more effective. Targeted therapies for HR-positive breast cancers include:

  • CDK4/6 inhibitors block proteins called cyclin-dependent kinases 4 and 6 (CDK4 and CDK6). This helps stop cancer cells from dividing and growing. CDK4/6 inhibitors include:
    • palbociclib (Ibrance)
    • ribociclib (Kisqali)
    • abemaciclib (Verzenio)
  • mTOR inhibitors block mTOR, a protein that helps cells grow and divide. Everolimus (Afinitor) is a mTOR inhibitor.
  • PI3K inhibitors block PI3K proteins in cancer cells, which can help prevent them from growing. Alpelisib (Piqray) is a PI3K inhibitor.

Targeted therapies for HER2-positive breast cancers

About 15% to 20% of breast cancers are HER2-positive. Targeted therapies for HER2-positive breast cancers include:

  • Monoclonal antibodies attach to the HER2 protein on cancer cells, which helps stop them from growing. Monoclonal antibodies include:
    • trastuzumab (Herceptin)
    • pertuzumab (Perjeta)
    • margetuximab (Margenza)
  • Antibody-drug conjugates (ADC) are monoclonal antibodies combined with a chemo drug. The HER2 antibody attaches to the HER2 protein and brings the chemo drug directly to it. ADCs include:
    • ado-trastuzumab emtansine (Kadcyla)
    • fam-trastuzumab deruxtecan (Enhertu)
  • Kinase inhibitors block a type of protein called kinase, which help cancer cells grow. HER2 is a kinase. Kinases inhibitors include:
    • lapatinib (Tykerb)
    • neratinib (Nerlynx)
    • tucatinib (Tukysa)

Targeted therapies for triple-negative breast cancers

Some types of breast cancer are considered triple-negative (TNBC). This means that they are HR-negative and HER2-negative breast cancer. Drugs that target estrogen receptors, progesterone receptors, or the HER2 protein aren’t effective for TNBC.

An antibody-drug conjugate called sacituzumab govitecan (Trodelvy) may be prescribed for advanced TNBC, after at least two other chemotherapy therapies have been tried. This ADC attaches to the Trop-2 protein and brings chemotherapy to it.

If you have HER2-negative breast cancer and also carry a BRCA gene mutation, targeted treatment may include PARP inhibitors such as olaparib (Lynparza) and talazoparib (Talzenna). PARP proteins help repair DNA damage in cells. Blocking these proteins in cancer cells can stop them from repairing DNA in tumor cells.

One of the newest targeted therapies is an ADC called fam-trastuzumab-deruxtecan-nxki (Enhertu). Approved by the Food & Drug Administration (FDA) in 2022, it’s the first targeted therapy for HER2-low breast cancer. This category may include some people with a previous diagnosis of TNBC.

Targeted therapies target molecules that tell cancer cells to grow and divide, but they work in different ways.

For example, SERMs attach to estrogen receptors and block estrogen from working with cancer cells. SERDs bind tight enough to hormone receptors to break them down. Aromatase inhibitors stop aromatase from changing other hormones into estrogen, which lowers estrogen production in the body.

CDK4/6, mTOR, P13K, and kinase inhibitors block specific proteins that fuel cancer cells. And PARP inhibitors help destroy tumor cells that have mutated BRCA genes.

Monoclonal antibodies lock on to the HER2 protein on cancer cells, which stops them from growing. And ADCs use monoclonal antibodies to carry chemo directly to proteins on cancer cells.

Is targeted therapy good for early breast cancer?

It depends on the type of breast cancer. For example:

  • trastuzumab and pertuzumab can treat early HER2-positive breast cancer.
  • olaparib can be given to people with early-stage HER2-negative breast cancer and a BRCA mutation.
  • ademaciclib can treat early-stage breast cancer that is HR-positive, HER2-negative with a high chance of coming back after surgery.
  • tamoxifen and aromatase inhibitors are among the hormone treatments for early HR-positive breast cancer.

The FDA approves each drug for a specific set of circumstances. Some are only for advanced breast cancers. And some are only for use when other therapies aren’t working.

You may get targeted therapy alone or in combination with:

  • surgery
  • chemotherapy
  • radiation therapy

Some targeted drugs are pills you can take at home. Some require an injection. Others you get intravenously (IV) or in the hospital.

Depending on the overall treatment plan, your therapy schedule could be daily, weekly, or monthly. Some IV treatments are given in cycles like chemotherapy. You get a treatment followed by a period of rest, then another treatment.

As you progress through treatment your doctor will monitor your progress. This may involve periodic blood tests or imaging scans to see if therapy is working.

Chemotherapy works by destroying rapidly dividing cells. In the process, it can harm healthy cells. With a specific focus, targeted therapies are less likely to harm normal cells. Side effects of targeted therapy tend to be different than side effects of chemotherapy. And they can vary according to factors such as:

  • the specific drug or combination of drugs
  • whether you’re having chemo at the same time
  • the dose and how it’s administered
  • your age and overall health
  • how your body reacts

Some people have only a few mild side effects and others may experience severe side effects. These may include:

  • nausea
  • vomiting
  • mouth sores
  • hair loss
  • diarrhea
  • constipation
  • loss of appetite
  • weight loss
  • headache
  • skin rash
  • fatigue
  • low blood cell counts
  • damage to the liver, lungs, or heart

Some types of targeted therapies can cause heart damage during and after treatment. Your doctor may perform regular tests to check your heart function while you’re undergoing treatment.

Many side effects tend to clear up when treatment ends. You can speak with a doctor about ways to relieve any uncomfortable side effects you may be experiencing.

Targeted therapies can be effective in treating breast cancer. But there’s no guarantee of success. A cancerous tumor can have multiple pathways to grow and spread. And cancer cells continue to mutate, which can lead to drug resistance.

Breast cancer mortality rates have been on a steady decline since the 1970s as new therapies emerge. The success rate varies, depending on factors such as:

  • type of breast cancer
  • stage at diagnosis
  • specific targeted drugs
  • other treatments
  • age and overall health

Targeted therapy is one of the newest ways to treat breast cancer and the focus of ongoing study.

Current targeted therapies for breast cancer target estrogen receptors, progesterone receptors, the HER2 protein, and BRCA gene mutations. As researchers discover more targets, precision medicine for breast cancer will continue to move forward.

If you have breast cancer, your doctor will review the results of your biopsy and blood tests. This information will help determine if a targeted therapy is the right choice for you.