Targeted Therapy for Breast Cancer

As researchers learn more about changes in cells that cause cancer, they’ve been able to develop new types of drugs that specifically target these changes. Targeted drugs work differently from chemotherapy drugs and often have different side effects.

Like chemotherapy, these drugs enter the bloodstream and reach almost all areas of the body, which makes them useful against cancers that have spread to distant parts of the body. Targeted drugs sometimes work even when chemo drugs do not. Some targeted drugs can help other types of treatment work better.

Targeted therapy for HER2-positive breast cancer

In about 1 in 5 women with breast cancer, the cancer cells have too much of a growth-promoting protein known as HER2 on their surface. These cancers, known as HER2-positive breast cancers, tend to grow and spread more aggressively. A number of drugs have been developed that target this protein.

Trastuzumab (Herceptin)

This is a monoclonal antibody, which is a man-made version of a very specific immune system protein. (In this case, the antibody is directed against the HER2 protein.)

This drug is often given with chemo, but it might also be used alone (especially if chemo alone has already been tried). Trastuzumab can be used to treat both early-stage and advanced breast cancer. When started before (neoadjuvant) or after (adjuvant) surgery to treat early breast cancer, this drug is usually given for 6 months to a year. For advanced breast cancer, treatment is often given for as long as the drug is helpful. This drug is given into a vein (IV) and is infused over 30to 90 minutes.

Another type of trastuzumab called trastuzumab and hyaluronidase injection (Herceptin Hylecta) is also available. It is given as a subcutaneous (under the skin) shot that takes about 2 to 5 minutes to inject.

Pertuzumab (Perjeta)

This monoclonal antibody can be given with trastuzumab and chemo, either before or after surgery to treat early-stage breast cancer, or to treat advanced breast cancer. This drug is given into a vein (IV).

Ado-trastuzumab emtansine (Kadcyla or TDM-1)

This is a monoclonal antibody attached to a chemotherapy drug (known as an antibody-drug conjugate). The anti-HER2 antibody acts like a homing signal by attaching to the HER2 protein on cancer cells, bringing the chemo directly to them.

This drug is used by itself to treat early-stage breast cancer (when neoadjuvant chemo was given and there was cancer still present at the time of surgery) or advanced breast cancer in women who have already been treated with trastuzumab and chemo. This drug is given in a vein (IV).

Fam-trastuzumab deruxtecan (Enhertu)

This is another antibody-drug conjugate, in which the anti-HER2 antibody attaches to the HER2 protein on cancer cells, bringing the chemo part of the drug directly to them. 

This drug can be used by itself to treat breast cancer that can’t be removed with surgery or that has spread (metastasized) to another part of the body,  typically after at least 2 other anti-HER2 targeted drugs have been tried. This drug is given in a vein (IV).

Lapatinib (Tykerb)

This is a kinase inhibitor. It is a pill taken daily. Lapatinib is used to treat advanced breast cancer, and might be used with certain chemotherapy drugs or hormone therapy drugs.

Neratinib (Nerlynx)

This is another kinase inhibitor. It is a pill taken daily. Neratinib is used to treat early-stage breast cancer after a woman has completed one year of trastuzumab and is usually given for one year. Some clinical trials show that it may also be effective in advanced breast cancer, as well.

Side effects HER2 targeted therapy drugs

The side effects of these drugs are often mild, but some can be serious. Discuss what you can expect with your doctor.

Some women develop heart damage during or after treatment with trastuzumab, pertuzumab, or ado-trastuzumab emtansine. This can lead to congestive heart failure. For most (but not all) women, this effect lasts a short time and gets better when the drug is stopped. The risk of heart problems is higher when these drugs are given with certain chemo drugs that also can cause heart damage, such as doxorubicin (Adriamycin) and epirubicin (Ellence). Because these drugs can cause heart damage, doctors often check your heart function (with an echocardiogram or a MUGA scan) before treatment, and regularly while you are taking the drug. Let your doctor know if you develop symptoms such as shortness of breath, leg swelling, and severe fatigue.

Lapatinib, neratinib and the combination of pertuzumab with trastuzumab can cause severe diarrhea, so it’s very important to let your health care team know about any changes in bowel habits as soon as they happen. Lapatinib can also cause hand-foot syndrome, in which the hands and feet become sore and red, and may blister and peel.

Fam-trastuzumab deruxtecan (Enhertu) can also cause serious lung disease in some women. In some cases this might even be life threatening. It’s very important to let your doctor or nurse know right away if you’re having symptoms such as coughing, wheezing, trouble breathing, or fever.  

If you are pregnant, you should not take these drugs. They can harm and even cause death to the fetus. If you could become pregnant, talk to your doctor about using effective birth control while taking these drugs.

Targeted therapy for hormone receptor-positive breast cancer

About 2 of 3 breast cancers are hormone receptor-positive (estrogen receptor-positive or progesterone receptor-positive). For women with these cancers, treatment with hormone therapy is often helpful. Certain targeted therapy drugs can make hormone therapy even more effective, although these targeted drugs might also add to the side effects.

CDK4/6 inhibitors

Palbociclib (Ibrance), ribociclib (Kisqali), and abemaciclib (Verzenio) are drugs that block proteins in the cell called cyclin-dependent kinases (CDKs), particularly CDK4 and CDK6. Blocking these proteins in hormone receptor-positive breast cancer cells helps stop the cells from dividing. This can slow cancer growth.

These drugs are approved for women with advanced hormone receptor-positive, HER2-negative breast cancer and are taken as pills, typically once or twice a day.

There are different ways to use these drugs.

  • Any of the three drugs can be given along with an aromatase inhibitor or fulvestrant to women who have gone through menopause.
  • Any of these three drugs can also be given with fulvestrant or an aromatase inhibitor to women who are still having regular periods (premenopausal) or are almost in menopause (perimenopausal). These women, however, must also be on medicines, such as luteinizing hormone-releasing hormone (LHRH) analogs, that stop the ovaries from making estrogen.
  • Abemaciclib can also be used by itself in women who have previously been treated with hormone therapy and chemotherapy.

The most common side effects are low blood cell counts and fatigue. Nausea and vomiting, mouth sores, hair loss, diarrhea, and headache are less common side effects. Very low white blood cell counts can increase the risk of serious infection. A rare but possible life-threatening side effect is inflammation of the lungs, also called interstitial lung disease or pneumonitis.

Everolimus (Afinitor)

Everolimus is used for women who have gone through menopause and have advanced hormone receptor-positive, HER2-negative breast cancer. It is used with the aromatase inhibitor exemestane (Aromasin) for women whose cancers have grown while being treated with either letrozole or anastrozole (or if the cancer started growing shortly after treatment with these drugs was stopped).

This targeted therapy drug blocks mTOR, a protein in cells that normally helps them grow and divide. Everolimus may also stop tumors from developing new blood vessels, which can help limit their growth. In treating breast cancer, this drug seems to help hormone therapy drugs work better. Everolimus is a pill that is taken once a day.

Common side effects of everolimus include mouth sores, diarrhea, nausea, feeling weak or tired, low blood counts, shortness of breath, and cough. Everolimus can also increase blood lipids (cholesterol and triglycerides) and blood sugars, so your doctor will check your blood work periodically while you are taking this drug. It can also increase your risk of serious infections, so your doctor will watch you closely for infection.

Targeted therapy for women with BRCA gene mutations

Olaparib (Lynparza) and talazoparib (Talzenna) are drugs known as PARP inhibitors. PARP proteins normally help repair damaged DNA inside cells. The BRCA genes (BRCA1 and BRCA2) also help repair DNA (in a slightly different way), but mutations in one of those genes can stop this from happening. PARP inhibitors work by blocking the PARP proteins. Because tumor cells with a mutated BRCA gene already have trouble repairing damaged DNA, blocking the PARP proteins often leads to the death of these cells.

Olaparib and talazoparib can be used to treat metastatic, HER2-negative breast cancer in women with a BRCA mutation who have already had chemotherapy. Olaparib can also be used in women who have already received hormone therapy if the cancer is hormone receptor-positive. Only a small portion of women with breast cancer have a mutated BRCA gene that they are both with, not acquired which is found only in the cancer. If you are not known to have a BRCA mutation, your doctor will test your blood to be sure you have one before starting treatment with this drug.

These drugs come in pills that are taken twice a day.

Side effects can include nausea, vomiting, diarrhea, fatigue, loss of appetite, taste changes, low red blood cell counts (anemia), low platelet counts, low white blood cell counts, belly pain, and muscle and joint pain. Rarely, some people treated with a PARP inhibitor have developed a blood cancer, such as myelodysplastic syndrome or acute myeloid leukemia (AML).

Targeted therapy for cancers with a PIK3CA gene mutation

Alpelisib (Piqray) is a targeted drug known as a PI3K inhibitor. It can be used along with fulvestrant to treat postmenopausal women with advanced hormone receptor-positive, HER2-negative breast cancer with a PIK3CA mutation that has grown during or after treatment with an aromatase inhibitor. About 30% to 40% of breast cancers have a mutated PIK3CA gene. Your doctor will test your blood or tumor for this mutation before starting treatment with this drug.

This drug is a pill taken once a day.

Side effects can include high blood sugar levels, signs of kidney, liver, or pancreatic problems, diarrhea, rash, low blood counts, nausea and vomiting, fatigue, decreased appetite, mouth sores, weight loss, low calcium levels, blood clotting problems, and hair loss. Very severe skin reactions, such as rashes with peeling and blistering, are possible and should be reported to a doctor. Patients with a history of severe skin reactions should tell their doctor before taking alpelisib.

More information about targeted therapy

To learn more about how targeted drugs are used to treat cancer, see Targeted Cancer Therapy.

To learn about some of the side effects listed here and how to manage them, see Managing Cancer-related Side Effects.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Almuwaqqat Z, Meisel JL, Barac A, Parashar S. Breast Cancer and Heart Failure. Heart Fail Clin. 2019 Jan;15(1):65-75.

Baselga J, Campone M, Piccart M, et al. Everolimus in postmenopausal hormone-receptor-positive advanced breast cancer. N Engl J Med. 2012;366:520−529.

Chan A, Delaloge S, Holmes FA, Moy B, Iwata H, Harvey VJ et al. Neratinib after trastuzumab-based adjuvant therapy in patients with HER2-positive breast cancer (ExteNET): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial. Lancet Oncol. 2016 Mar;17(3):367-77.

Freedman RA et al. TBCRC 022: Phase II trial of neratinib + capecitabine for patients (Pts) with human epidermal growth factor receptor 2 (HER2+) breast cancer brain metastases (BCBM). J Clin Oncol 35, 2017 (suppl; abstr 1005). 

Gao et al. Sci. Signal. 2013 & Cerami et al. Cancer Discov. 2012. Accessed at on May 29, 2019. 

Henry NL, Shah PD, Haider I, Freer PE, Jagsi R, Sabel MS. Chapter 88: Cancer of the Breast. In: Niederhuber JE, Armitage JO, Doroshow JH, Kastan MB, Tepper JE, eds. Abeloff’s Clinical Oncology. 6th ed. Philadelphia, Pa: Elsevier; 2020.

Jagsi R, King TA, Lehman C, Morrow M, Harris JR, Burstein HJ. Chapter 79: Malignant Tumors of the Breast. In: DeVita VT, Lawrence TS, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg’s Cancer: Principles and Practice of Oncology. 11th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2019.

Ma CX and Sparano JA. Treatment approach to metastatic hormone receptor-positive, HER2-negative breast cancer: Endocrine therapy and targeted therapy. Last updated Jun 12, 2019. Accessed August 10, 2019.

Mukohara T. PI3K mutations in breast cancer: prognostic and therapeutic implications. Breast Cancer (Dove Med Press). 2015;7: 111–123.

National Cancer Institute. Physician Data Query (PDQ). Breast Cancer Treatment – Health Professional Version. 2019. Accessed at on August 9, 2019.

National Comprehensive Cancer Network (NCCN). Practice Guidelines in Oncology: Breast Cancer. Version 2.2019. Accessed at on July 28, 2019.

Schott AF. Systemic treatment for HER2-positive metastatic breast cancer. Last updated Jun 11, 2019. Accessed August 10, 2019.

Last Medical Review: September 18, 2019 Last Revised: December 23, 2019

American Cancer Society medical information is copyrighted material. For reprint requests, please see our Content Usage Policy.