Targeted Therapy for Breast Cancer

As researchers have learned more about changes in cancer cells that cause them to grow out of control, they’ve developed new types of drugs that target some of these cell changes. These targeted drugs are designed to block the growth and spread of cancer cells. These drugs work differently from chemotherapy drugs, which attack all cells that are growing quickly (including cancer cells).

Targeted drugs sometimes work even when chemo drugs do not. Some targeted drugs can help other types of treatment work better. Targeted drugs also tend to have different side effects than chemo.

Targeted therapy for HER2-positive breast cancer

For about 1 in 5 women with breast cancer, the cancer cells have too much of a growth-promoting protein known as HER2/neu (or just 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. It is often given along 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- and late-stage breast cancer. When started before or after surgery to treat early breast cancer, this drug is usually given for a total of 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).
  • Pertuzumab (Perjeta): This monoclonal antibody can be given with trastuzumab and chemo, either before 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, also known as TDM-1): This is a monoclonal antibody attached to a chemotherapy drug. It is used by itself to treat advanced breast cancer in women who have already been treated with trastuzumab and chemo. This drug is also 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 along with certain chemotherapy drugs, trastuzumab, or hormone therapy drugs.
  • Neratinib (Nerlynx): This is another kinase inhibitor. It is a pill that is 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 of targeted therapy for HER2-positive breast cancer

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 again 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 and neratinib 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. Pertuzumab can also cause diarrhea.  

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 (ER-positive or PR-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.

Palbociclib and ribociclib are approved for women who have gone through menopause and have advanced hormone receptor-positive, HER2-negative breast cancer. They are used along with certain hormone therapy drugs such as fulvestrant or an aromatase inhibitor (such as letrozole). These drugs are taken as pills, typically once a day for 3 weeks at a time, with a week off before starting again.

Abemaciclib is approved for use with fulvestrant in women who have gone through menopause with advanced hormone receptor-positive, HER2-negative breast cancer that has gotten worse after hormone therapy. It can also be given without fulvestrant in women who have previously been treated with hormone therapy and chemotherapy. Abemaciclib is taken as pills, typically twice a day.

Side effects of these drugs tend to be mild. 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.

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 along 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.

Everolimus is also being studied for use in earlier-stage breast cancer, with other hormone therapy drugs, and in combination with other treatments.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

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Last Medical Review: July 1, 2017 Last Revised: October 16, 2017

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