Targeted Therapy for Breast Cancer

April 10, 2025

This page was reviewed under our medical and editorial policy by Susan Yost, Ph.D., staff scientist, Department of Medical Oncology & Therapeutics Research, City of Hope^® Cancer Center Duarte

Targeted therapy works on particular molecules that breast cancer cells use to grow. It may be a treatment option for patients with breast cancer depending on the type of breast cancer. Sometimes it is used on its own, and other times it may be recommended along with other treatments, such as chemotherapy.

Doctors and patients work together to determine the optimal breast cancer treatment plan and when targeted therapy may be beneficial.

What Is Targeted Therapy for Breast Cancer?

Targeted therapies for breast cancer are typically either monoclonal antibodies or drugs made up of small molecules, as detailed below.

Monoclonal antibodies: These are lab-created proteins that work like a person’s own antibodies. Antibodies are proteins that seek out and fight foreign substances, such as cancer cells.

Small-molecule drugs: These therapies zero in on targets inside cancer cells. Because of their small size, these drugs are able to travel easily into cancer cells.

Targeted therapy for breast cancer stops cancer growth by:

• Blocking signals that tell cells to grow and multiply
• Preventing the growth of blood vessels
• Sending substances that destroy cells directly to the cancer
• Preventing certain hormones needed for growth from reaching the cancer cells
• Using a person’s immune system to destroy the cancer cells

Types of Targeted Therapy for Breast Cancer

Targeted therapies for breast cancer fall into eight broad categories. The length of treatment may vary, depending on a patient’s response to the drug, including side effects.

AKT (Serine/Threonine Kinase) Inhibitor

Truqap^™ (capivasertib) thwarts cancer growth by preventing a protein known as AKT from communicating with cancer cells. It may be used with Faslodex^® (fulvestrant) to treat advanced HER2-negative breast cancer that is hormone-receptor positive, meaning it relies on the hormones estrogen or progesterone to grow. (HER2 is a protein known as a kinase involved in the growth and repair of breast cells.) Before starting treatment, doctors check a blood or tumor sample to see if the cancer has mutations in the PIK3CA, AKT1 or PTEN genes. Truqap^™ is a tablet taken twice daily for four days followed by three days off each week.

Antibody-Drug Conjugate (ADC)

These medications combine a monoclonal antibody with a chemotherapy drug to deliver chemotherapy straight to the cancer cells. Three ADC treatments are available to treat breast cancer.

Kadcyla^® (ado-trastuzumab emtansine) links the HER2 antibody to the chemotherapy medication emtansine. It is administered once every three weeks via intravenous (IV) infusion and is used to treat:

• Early-stage breast cancer that remains after surgery, when chemotherapy and Herceptin^® (trastuzumab) are given beforehand
• Advanced-stage cancer after treatment with Herceptin® and chemotherapy

Enhertu^® (fam-trastuzumab deruxtecan), given as an IV infusion once every three weeks, joins the HER2 antibody to deruxtecan, a chemotherapy drug. It is used to treat breast cancer that is:

• HER2-positive and has spread or is unable to be removed with surgery (and after another anti-HER2 drug has been tried)
• HER2-low and has spread or is unable to be removed surgically (typically after chemotherapy has been tried or if breast cancer returns within six months of completing chemotherapy)

Trodelvy^® (sacituzumab govitecan-hziy) is a conjugated monoclonal antibody that attaches to a protein on breast cancer cells known as Trop-2. Levels of this protein are high in triple-negative breast cancer. When Trodelvy^® and Trop-2 interact, a chemotherapy drug known as SN-38 is released, destroying the cancer cell. Trodelvy^® is used for locally advanced or metastatic breast cancer that is unable to be treated with surgery. It is given as an IV infusion on the first and eighth days of a 21-day treatment cycle. The cycle may be repeated.

CDK4/6 Inhibitors

These drugs block proteins in cancer cells called cyclin-dependent kinases that prevent hormone receptor-positive breast cancer cells from dividing — especially those known as CDK4 and CDK6. Three drugs are in this class:

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

These drugs may be used to treat advanced breast cancer in women who have gone through menopause. These patients receive the medication along with fulvestrant, a hormone therapy drug, or an aromatase inhibitor, such as Femara^® (letrozole).

They may also be used to treat advanced breast cancer in women who are still having menstrual periods. Besides fulvestrant or an aromatase inhibitor, these women must either receive medications to stop the ovaries from making estrogen or their ovaries must be surgically removed.

Verzenio^® may be prescribed alone for advanced breast cancer after hormone therapy and chemotherapy have been tried. It may also be used for early-stage breast cancer that has spread to lymph nodes. In this case, it is given along with tamoxifen or an aromatase inhibitor. Verzenio^® is a tablet that is typically taken twice daily for up to two years.

Ibrance^® is a capsule that is typically taken by mouth once daily for 21 consecutive days followed by seven days off treatment.

Kisqali^® is an oral tablet typically taken once daily for 21 consecutive days followed by seven days off treatment.

Kinase Inhibitors

Kinases transmit signals to a cell. HER2 is a kinase that tells cancer cells to grow. Kinase inhibitors block this signal, which stops the growth of cancer. Three kinase inhibitors, listed below, may be used to treat breast cancer.

Tykerb^® (lapatinib): This therapy is taken by mouth once daily, either continuously or in cycles. It is given along with the drug capecitabine to treat some advanced or metastatic breast cancers after other treatments have been tried. It may also be given along with the hormone therapy drug letrozole.

Nerlynx^® (neratinib): This oral tablet is taken once daily, either continuously or in cycles for up to one year. For early-stage HER2-positive breast cancer, it is given alone after trastuzumab. For patients with advanced or metastatic HER2-positive breast cancer, Nerlynx^® is given along with capecitabine.

Tukysa^® (tucatinib): This oral tablet is taken twice daily to treat HER2-positive breast cancer that has spread or is unable to be surgically removed. It is given along with the drugs trastuzumab and capecitabine after other anti-HER2 drugs have been tried.

Monoclonal Antibodies

These drugs are lab-made proteins designed to mimic the immune system’s own antibodies. They seek out and attach to the HER2 protein on cancer cells to stop cancer growth.

Herceptin^® (trastuzumab) may be used alone or with chemotherapy to treat early-stage and advanced breast cancer. It is given as an IV infusion either once weekly for 12 to 18 weeks or once every three weeks for a year. Another form of the medication, known as Herceptin Hylecta^™, is injected under the skin.

Perjeta^® (pertuzumab) may be used with trastuzumab and chemotherapy, either before or after surgery. Used to treat both early-stage breast cancer and advanced breast cancer, Perjeta^® is given as an IV infusion once every three weeks.

Margenza^® (margetuximab) may be used along with chemotherapy to treat metastatic breast cancer. Typically, at least two other anti-HER2 drugs have already been tried. Margenza is given as an IV infusion once every three weeks.

Phesgo^® (trastuzumab, pertuzumab and hyaluronidase), an under-the-skin injection, may be used along with chemotherapy to treat early-stage or metastatic breast cancer. It is given once every three weeks.

mTOR Inhibitor

MTOR is a protein found in cells that helps them divide and grow. Afinitor^® (everolimus) blocks mTOR, limiting tumor growth by preventing the formation of new blood vessels. Afinitor^® is an mTOR inhibitor used to treat HER2-negative advanced breast cancer that is hormone receptor-positive in postmenopausal women. It is taken as a tablet once daily.

PARP Inhibitors

Certain cancers have defects in BRCA1 and BRCA2, which are genes that repair DNA. PARP, or poly (ADP-ribose) polymerase enzymes, also plays a role in DNA growth and repair of cells but in a different way. Blocking PARP may cause death of cancer cells in people with a BRCA mutation. Before starting therapy with PARP inhibitor drugs, doctors do a blood test to see if the patient has a BRCA mutation.

Lynparza^® (olaparib) is used to treat both early-stage and metastatic BRCA-mutated HER2-negative breast cancer. It comes as an oral tablet that is taken twice daily.

Talzenna^® (talazoparib) is used to treat advanced or metastatic BRCA-mutated HER2-negative breast cancer. It comes as an oral capsule that is taken once daily.

PI3K Inhibitor

PI3K stands for phosphatidylinositol 3-kinase, which is a protein found in cancer cells. Blocking PI3K stops the growth of cancer cells. Piqray^® (alpelisib) is a PI3K inhibitor that is used with fulvestrant to treat HER2-negative, hormone receptor-positive advanced breast cancers. It is used when there is a PIK3CA gene mutation that is found during or after treatment with an aromatase inhibitor. Before starting treatment with Piqray^®, doctors test a person’s blood or tumor for a PIK3CA mutation. This drug comes as an oral tablet that is taken once daily.

Risks and Side Effects

Side effects of targeted therapies vary, depending on many factors, such as the types and combinations of treatments and treatment length. Not everyone experiences the same side effects.

In addition to changes in certain lab values that the care team will monitor, side effects of targeted therapies for breast cancer may include the following.

• Anemia (Verzenio^®, Perjeta^®)
• Back and joint pain (Nerlynx^® when used with capecitabine)
• Back pain (Kisqali^®)
• Belly pain (Enhertu^®, Verzenio^®, Tukysa^® when used with trastuzumab, Margenza^® when given with chemotherapy, Afinitor^®, Lynparza^® in combination with other drugs)
• Belly pain or swelling (Nerlynx^®)
• Bleeding (Kadcyla^®)
• Blisters and redness on the palms of the hands and soles of the feet (Tykerb^®, Tukysa^® when used with trastuzumab and capecitabine, Margenza^® when given with chemotherapy)
• Bone fractures (Talzenna^® when given along with other drugs)
• Change in taste (Lynparza^®, Talzenna^® when given along with other drugs)
• Chills and fever (Herceptin^®)
• Congestive heart failure and serious lung problems, which may be long term (Herceptin^®)
• Constipation (Kadcyla^®, Enhertu^®, Trodelvy^®, Kisqali^®, Nerlynx^® when used with capecitabine, Margenza^® when given with chemotherapy)
• Cough (Herceptin^®, Afinitor^®)
• Cough and shortness of breath (Margenza^® when given with chemotherapy, Lynparza^®)
• Decreased appetite (Trodelvy^®, Nerlynx^®, Tukysa^® when used with trastuzumab and capecitabine, Afinitor^®, Lynparza^®, Talzenna^®, Piqray^®)
• Diarrhea (Truqap^™, Enhertu^®, Verzenio^®, Ibrance^®, Kisqali^®, Tykerb^®, Nerlynx^®, Tukysa^®, Herceptin^®, Margenza^® when given with chemotherapy, Afinitor^®, Lynparza^®, Piqray^®)
• Diarrhea or constipation (Perjeta^®)
• Diarrhea, which may become severe (Trodelvy^®, Phesgo^®, Talzenna^®)
• Dizziness (Nerlynx^® when used with capecitabine, Lynparza^®, Talzenna^® when given along with other drugs)
• Fatigue (Truqap^™, Kadcyla^®, Enhertu^®, Trodelvy^®, Verzenio^®, Ibrance^®, Kisqali^®, Tykerb^®, Nerlynx^®, Tukysa^® when used with trastuzumab, Perjeta^®, Phesgo^®, Afinitor^®, Talzenna^®, Piqray^®)
• Fatigue and weakness (Margenza^® when given with chemotherapy, Lynparza^®)
• Fever (Ibrance^®, Tukysa^® when used with trastuzumab, Margenza^® when given with chemotherapy, Afinitor^®)
• Hair loss (Enhertu^®, Trodelvy^®, Verzenio^®, Ibrance^®, Kisqali^®, Perjeta^®, Margenza® when given with chemotherapy, Phesgo^®, Talzenna^®, Piqray^®)
• Headache (Kadcyla^®, Verzenio^®, Kisqali^®, Herceptin^®, Perjeta^®, Margenza^® when given with chemotherapy, Afinitor^®, Lynparza^®, Talzenna^®)
• Infections (Verzenio^®, Ibrance^®, Kisqali^®, Herceptin^®, Afinitor^®)
• Infusion-related reactions (Tukysa^® when used with trastuzumab, Margenza^® when given with chemotherapy)
• Insomnia (Herceptin^®)
• Lack of appetite (Enhertu^®, Verzenio^®, Ibrance^®, Margenza^® when given with chemotherapy)
• Life-threatening low white blood cell count (Trodelvy^®)
• Mouth sores (Ibrance®, Nerlynx®, Afinitor®, Piqray^®)
• Muscle aches (Perjeta^®)
• Muscle and joint pain (Kadcyla^®, Enhertu^®, Margenza^® when given with chemotherapy)
• Muscle spasms (Nerlynx^®)
• Nail and skin problems (Nerlynx^®)
• Nausea (Kadcyla^®, Nerlynx^®, Tukysa^® when used with trastuzumab, Herceptin^®, Phesgo^®, Afinitor^®, Lynparza^®, Talzenna^® when given along with other drugs)
• Nausea and vomiting (Truqap^™, Enhertu^®, Trodelvy^®, Verzenio^®, Ibrance^®, Kisqali^®, Tykerb^®, Tukysa^® when used with trastuzumab and capecitabine, Perjeta^®, Margenza^® when given with chemotherapy, Nerlynx^®, Talzenna^®, Piqray^®)
• Nosebleeds (Nerlynx^®)
• Pain in the arms and legs (Margenza^® when given with chemotherapy)
• Rarely, serious liver and heart problems, which may be long term (Kadcyla^®)
• Rash (Ibrance^®, Kisqali^®, Kisqali^®, Tykerb^®, Nerlynx^®, Tukysa^®, Herceptin^®, Perjeta^®, Phesgo^®, Afinitor^®, Piqray^®)
• Serious heart and lung problems, which may be long term (Phesgo^®)
• Serious heart problems, which may be long term (Perjeta^®, Margenza^® when given with chemotherapy)
• Serious liver problems, which may be long term (Tykerb^®)
• Serious lung problems, which may be fatal (Enhertu^®)
• Skin reactions (Truqap^™)
• Sores inside the mouth (Truqap^™, Tukysa^® when used with trastuzumab and capecitabine)
• Swelling (Afinitor^®)
• Swelling inside the mouth (Perjeta^®)
• Tingling in the hands and feet (Perjeta^®, Margenza^® when given with chemotherapy, Phesgo^®)
• Upper respiratory tract infection (Nerlynx^® when used with capecitabine)
• Upset stomach (Lynparza^®)
• Urinary tract infection (Nerlynx^®, Lynparza^® in combination with other drugs)
• Vomiting (Lynparza^®)
• Weakness (Ibrance^®, Perjeta^®, Phesgo^®, Afinitor^®)
• Weight loss (Nerlynx^®, Piqray^®)

In addition to the above side effects, the CDK4/6 inhibitor class of drugs may rarely cause a serious lung problem known as interstitial pneumonitis.