Targeted Therapy

Targeted therapy is a form of precision medicine. It is a type of treatment that stops or slows cancer cell growth.¹

Targeted therapies are considered a systemic treatment because they go through the body to where the cancer cells are located. Other systemic treatments, like chemotherapy, work more broadly throughout the body.¹

How is targeted therapy different from chemotherapy?

Chemotherapy focuses on any cell that grows quickly. Cancer cells divide and grow quickly, but so do many healthy cells. This includes cells in the digestive tract, hair, bone marrow, and blood. In the process of damaging cancer cells, chemotherapy can cause damage to those healthy cells. This damage can cause side effects like hair loss and nausea.²

In contrast, targeted therapies focus on other specific features of cancer cells. In this way, targeted therapy attempts to treat the cancer while doing less damage to normal cells and causing fewer side effects.¹

Another difference between targeted therapy and chemotherapy is that targeted therapies generally block the growth and division of cancer cells. In contrast, chemotherapy typically kills cancer cells. In some cases, targeted therapy and chemotherapy may be used in combination to treat breast cancer.^1,2

There are many types of targeted therapy used for the treatment of certain early-stage, advanced, and/or metastatic breast cancers. These therapies pinpoint different targets associated with breast cancer, including:¹

• HER2-targeting agents
• CDK4/6 inhibitors
• PARP inhibitors
• mTOR inhibitors
• PI3K inhibitors
• Antibody-drug conjugates

HER2 targeted therapy

Some breast cancer cells have too much human epidermal growth factor receptor 2 (HER2). These are known as HER2-positive breast cancers. This type of breast cancer is usually aggressive. It tends to grow quickly and spread (metastasize).¹

Several treatments target the HER2 receptor, including:^1,3

• Herceptin® (trastuzumab)
• Kadcyla® (ado-trastuzumab emtansine)
• Nerlynx® (neratinib)
• Perjeta® (pertuzumab)
• Ogivri® (trastuzumab-dkst)
• Tykerb® (lapatinib)
• Herzuma® (trastuzumab-pkrb)
• Ontruzant® (trastuzumab-dttb)
• Trazimera™ (trastuzumab-qyyp)
• Kanjinti™ (trastuzumab-anns)
• Herceptin Hylecta™ (trastuzumab and hyaluronidase-oysk)
• Enhertu® (fam-trastuzumab deruxtecan-nxki)
• Tukysa® (tucatinib)
• Phesgo™ (pertuzumab, trastuzumab, and hyaluronidase-zzxf)
• Margenza® (margetuximab-cmkb)

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors

CDK4 and CDK6 are proteins that are important during a cell’s growth and copying (replication) cycles. In breast cancer cells, CDK4 and CDK6 may be overactive, which may cause the cancer cells to grow uncontrollably. By blocking CDK4/6, these targeted therapies can help slow the growth and division of breast cancer cells.¹

CDK4/6 inhibitors for breast cancer include:¹

• Ibrance® (palbociclib)
• Kisqali® (ribociclib)
• Verzenio® (abemaciclib)

Poly (ADP-ribose) polymerase (PARP) inhibitors

PARP enzymes are important for cellular functions like DNA repair. DNA is copied every time a cell divides. And the rapid growth of cancer cells creates more chances for DNA damage to occur.¹

Damage to the DNA of cells, including cancer cells, can lead to cell death. Normally, cells have several ways of repairing damage that may occur to the DNA. By blocking the PARP repair function, PARP inhibitors can limit the cancer cells' ability to repair the DNA. In this way, they can lead to the death of cancer cells.¹

Two such PARP inhibitors available to treat certain forms of breast cancer are:¹

• Lynparza® (olaparib)
• Talzenna® (talazoparib)

Mechanistic target of rapamycin (mTOR) inhibitors

mTOR is a protein that is normally involved in a cell’s ability to divide. mTOR often changes (mutates) in breast cancer cells. This mutation can fuel cancer growth. mTOR inhibitors block this process and can slow the growth of breast cancers.^1,4

One mTOR inhibitor available to treat certain forms of advanced breast cancer is:¹

• Afinitor® (everolimus)

PI3K inhibitors

PIK3CA is one of the most commonly mutated genes in breast cancer. About 30 to 40 percent of people living with breast cancer have this mutation.¹

Piqray® (alpelisib) is approved to treat certain forms of advanced or metastatic hormone receptor-positive and HER2-negative breast cancer with a mutation in the PIK3CA gene.¹

Antibody-drug conjugates (ADCs)

An antibody-drug conjugate (ADC) is a monoclonal antibody combined with a specially designed chemotherapy drug. Generally, the antibody portion helps to find and attach to the specific type of breast cancer cells. Then, the chemotherapy portion is released to attack the cancer cell.¹

ADCs are used to treat certain forms of HER2-positive breast cancer, hormone receptor-positive breast cancer, triple-negative breast cancer, and HER2-low breast cancer. The type of cancer depends on the specific medicine. HER2-low is a newly defined subset of breast cancer.^1,5

ADCs for breast cancer include:^1,5

• Trodelvy® (sacituzumab govitecan-hziy) – The first ADC approved for certain forms of triple-negative breast cancer. It can also be used to treat certain forms of hormone receptor positive, HER2-negative breast cancer.
• Kadcyla® – Targets the HER2 receptor in the treatment of certain forms of HER2-positive breast cancer
• Enhertu® – Targets the HER2 receptor in the treatment of certain forms of HER2-positive breast cancer. It is also the first approved therapy for people with certain forms of HER2-low breast cancer.

Side effects of targeted therapies

While the goal of targeted therapies is to cause fewer side effects, these therapies still can lead to side effects. Side effects vary depending on the specific drug. But common side effects of some targeted therapies include:¹

• Diarrhea
• Fatigue
• Hair loss
• Nausea and vomiting
• Skin or nail problems, including rashes or discoloration of nails
• Reductions in the number of red blood cells, white blood cells, and/or platelets

These are not all the possible side effects of targeted therapies. Talk to your doctor about what to expect when taking targeted therapies. You also should call your doctor if you have any changes that concern you when taking one of these drugs.

Before beginning treatment for breast cancer, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you take. This includes over-the-counter drugs.