Breast cancer

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Targeted therapy for breast cancer

Targeted therapy is usually used to treat breast cancer. It uses drugs to target specific molecules (such as proteins) on cancer cells or inside them. These molecules help send signals that tell cells to grow or divide. By targeting these molecules, the drugs stop the growth and spread of cancer cells and limit harm to normal cells. Targeted therapy may also be called molecular targeted therapy.

You may have targeted therapy to:

  • stop breast cancer cells from growing and spreading
  • treat breast cancer that has spread (metastasized) to other parts of the body and that no longer responds to other breast cancer treatments

Your healthcare team will consider your personal needs to plan the drugs, doses and schedules of targeted therapy. You may also receive other treatments.

HER2 targeted therapy drugs

ERBB2 is a gene that has changed (mutated), so that it helps a tumour grow (called an oncogene). It is more commonly known as HER2 (or HER2/neu). HER2 stands for human epidermal growth factor receptor 2.

HER2 controls a protein on the surface of breast cells that helps them grow. Each healthy cell contains 2 copies of the HER2 gene. Sometimes too many copies of the HER2 gene are present in a cell and the body makes too much HER2 protein. This is called overexpression of HER2.

HER2 status testing is done on all breast cancer tumours at the time of diagnosis. If the breast cancer cells overexpress HER2, it is called HER2-positive breast cancer.

The following targeted therapy drugs have been specially designed to attach to the extra HER2 proteins to stop the growth of HER2-positive breast cancer cells.

Trastuzumab (Herceptin)

Trastuzumab is the most common targeted therapy drug used to treat HER2-positive breast cancer. It is given through a needle in a vein (intravenously).

Women with invasive or locally advanced breast cancer may be given trastuzumab in combination with chemotherapy drugs after surgery (called adjuvant therapy). Trastuzumab is usually given for up to a year after chemotherapy for breast cancer has finished.

Women with breast cancer that has spread to other parts of the body (called metastatic breast cancer) may be given trastuzumab by itself. It is continued until the breast cancer does not respond to the drug.

Pertuzumab (Perjeta)

Pertuzumab may be used in combination with trastuzumab and chemotherapy to treat early HER2-positive breast cancer in women with lymph node positive or hormone receptor-negative disease.

Pertuzumab may be used in combination with trastuzumab and docetaxel to treat metastatic HER2-positive breast cancer in women who have not had trastuzumab or chemotherapy to treat it.

Trastuzumab emtansine (Kadcyla or T-DM1)

Trastuzumab emtansine is a combination of trastuzumab and the chemotherapy drug emtansine (DM1). It may be used to treat HER2-positive metastatic breast cancer that has already been treated with one of the following:

  • trastuzumab alone
  • chemotherapy with paclitaxel (Taxol) or docetaxel
  • trastuzumab with either paclitaxel or docetaxel

Tyrosine kinase inhibitors

Tyrosine kinases are a type of enzyme (proteins that speed up certain chemical reactions in the body). They play an important role in cell development and division. Tyrosine kinase inhibitors block specific tyrosine kinases that tell cancer cells to grow. These drugs are also called signal-transduction inhibitors or small-molecule drugs.

Lapatinib (Tykerb)

Lapatinib and capecitabine (Xeloda) may be given to treat metastatic HER2-positive breast cancer when other types of chemotherapy or trastuzumab (Herceptin) no longer work.

Lapatinib and letrozole (Femara) may be given to post-menopausal women with HER2-positive and hormone receptor–positive metastatic breast cancer. Letrozole is a type of hormonal therapy. This combination is given when hormonal therapy stops working.

Palbociclib (Ibrance)

Palbociclib may be given with aromatase inhibitors to treat post-menopausal women with estrogen receptor–positive (ER+) and HER2-negative metastatic breast cancer. Palbociclib may not be covered by all provincial health plans.

Ribociclib succinate (Kisqali)

Ribociclib succinate may be given with letrozole to treat post-menopausal women with hormone receptor–positive and HER2-negative advanced or metastatic breast cancer.

Mammalian target of rapamycin (mTOR) inhibitors

mTOR inhibitors block the mammalian target of rapamyin (mTOR). mTOR is a protein that regulates cell growth and reproduction. It is abnormal in some types of cancer, including breast cancer, which causes cancer cells to keep growing and dividing. mTOR inhibitors block the action of mTOR, which can stop the growth of cancer.

Everolimus (Afinitor) is the mTOR inhibitor used for metastatic breast cancer. It is given with the hormonal therapy drug exemestane (Aromasin). This combination is used to treat post-menopausal women with hormone receptor–positive, HER2-negative metastatic breast cancer that no longer responds to hormonal therapy with letrozole or anastrozole (Arimidex).

Cyclin-dependent kinase (CDK) inhibitors

Cyclin-dependent kinases (CDKs) are proteins that control the cell cycle. CDK inhibitors block these proteins to help slow or stop the growth of cancer cells.

Abemaciclib (Verzenio) is a CDK inhibitor used in women with hormone receptor–positive, HER2-negative advanced or metastatic breast cancer. It is taken as pill daily and may be given:

  • with an aromatase inhibitor for post-menopausal women as hormonal-based therapy
  • with fulvestrant (Faslodex) if the disease progresses after hormonal therapy
  • alone if the disease progresses after hormonal therapy and at least 2 chemotherapy regimens

Targeted therapy for women with BRCA gene mutations

Olaparib (Lynparza) can be used to treat women with metastatic, HER2-negative breast cancer who have a BRCA gene mutation and have already had chemotherapy. Olaparib is usually taken by mouth.

Side effects

Side effects can happen with any type of treatment for breast cancer, but everyone’s experience is different. Some people have many side effects. Other people have few or none at all.

Targeted therapy attacks cancer cells but doesn’t usually damage healthy cells, so there are fewer and less severe side effects than with chemotherapy and radiation therapy. Chemotherapy and radiation therapy can damage healthy cells along with cancer cells.

If you develop side effects, they can happen any time during, immediately after or a few days or weeks after targeted therapy. Sometimes late side effects develop months or years after targeted therapy. Most side effects go away on their own or can be treated, but some side effects may last a long time or become permanent.

Side effects of targeted therapy will depend mainly on the type of drug or combination of drugs, the dose, how it’s given and your overall health. Some common side effects of targeted therapy for breast cancer are:

Some people may have a reaction when the drugs are given, including:

  • wheezing, difficulty breathing or coughing
  • skin rash, flushing or itching
  • anxiety
  • chest pain or irregular heartbeat
  • high or low blood pressure

Trastuzumab can cause heart damage, especially when it is given with doxorubicin (Adriamycin), which is a chemotherapy drug commonly used for breast cancer. Lapatinib can also cause heart damage. Heart function tests, such as a multigated acquisition (MUGA) scan or an echocardiogram, are done before the start of treatment and then regularly during treatment with trastuzumab.

Tell your healthcare team if you have these side effects or others you think might be from targeted therapy. The sooner you tell them of any problems, the sooner they can suggest ways to help you deal with them.

Information about specific cancer drugs


Questions to ask about targeted therapy

Find out more about targeted therapy. To make the decisions that are right for you, ask your healthcare team questions about targeted therapy.


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