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Targeted Therapy for Breast Cancer
Several types of targeted therapy drugs can be used to treat breast cancer.
Targeted therapy is the use of medicines that are directed at, or target, certain proteins on cancer cells that help the cancer cells grow, spread, and live longer. Targeted drugs work to destroy cancer cells or slow their growth. The side effects from these drugs are different from chemotherapy, and sometimes less severe.
Some targeted therapy drugs, such as monoclonal antibodies, work in more than one way to control cancer cells. These may also be considered immunotherapy because they boost the immune system.
Like chemotherapy, these drugs enter the bloodstream and reach almost all areas of your body. This makes them useful against cancers that have spread to distant parts of the body.
Targeted therapy for HER2-positive breast cancer
In about 15% to 20% of breast cancers, the cancer cells make too much of a growth-promoting protein called HER2. These cancers are known as HER2-positive breast cancers. They tend to grow and spread more aggressively than HER2-negative breast cancers.
Several types of drugs that target the HER2 protein can be used to treat these cancers.
Monoclonal antibodies
Monoclonal antibodies are human-made versions of immune system proteins (antibodies) that are designed to attach to a specific target. In this case, they attach to the HER2 protein on cancer cells. This can help stop the cells from growing.
Trastuzumab can be used to treat both early-stage and advanced breast cancer. This drug is often given with chemo, but it might be used by itself, especially if chemo alone has already been tried.
- For early breast cancer: When started before or after surgery to treat early breast cancer, this drug is usually given for a year.
- For advanced breast cancer: Treatment is often given for as long as the drug is helpful.
This drug is put into a vein (IV).
Another form of trastuzumab called trastuzumab and hyaluronidase injection (Herceptin Hylecta) is given as a subcutaneous shot (under the skin) over a period of a few minutes.
Pertuzumab can be given with trastuzumab and chemo:
- Before or after surgery to treat early-stage breast cancer
- To treat advanced breast cancer
It can also be used with the antibody-drug conjugate fam-trastuzumab deruxtecan as the first treatment for advanced breast cancer.
It is put into a vein (IV).
This combination of drugs is given as a subcutaneous shot (under the skin) over a period of several minutes.
This HER2 monoclonal antibody can be used along with chemo to treat advanced breast cancer. It is typically used after at least 2 other drugs that target HER2 have been tried.
It is put into a vein (IV).
Antibody-drug conjugates
An antibody-drug conjugate (ADC) is a type of cancer treatment that combines an antibody with chemotherapy in a single medication.
You can think of the antibody as a "guided delivery system." It recognizes and attaches to the HER2 protein on cancer cells, helping the medicine find the right target. Once attached, it delivers the chemotherapy directly into the cancer cell, where it can work to destroy it.
This targeted approach helps concentrate the treatment in cancer cells while reducing exposure to normal cells.
This antibody-drug conjugate connects the HER2 antibody to a chemo drug.
It is used by itself to treat:
- Early-stage breast cancer after surgery, when chemo and trastuzumab were given before surgery and cancer was still found in the tissue or tumor removed by surgery.
- Advanced breast cancer in people who have already been treated with trastuzumab and chemo.
This drug is put in a vein (IV).
This antibody-drug conjugate connects the HER2 antibody to a chemo drug. It is put in a vein (IV).
Early-stage breast cancer
This drug may be given to people with HER2-positive (IHC 3+ or FISH positive) early-stage breast cancer:
- As part of neoadjuvant treatment (before surgery) along with chemo, trastuzumab, and pertuzumab.
OR
- After surgery, if there was residual disease and the person was treated with chemo and trastuzumab before the surgery.
Advanced or metastatic breast cancer
This drug may be given to people with HER2-positive (IHC 3+ or FISH positive) advanced or metastatic breast cancer:
- As part of the first treatment along with pertuzumab (see monoclonal antibodies, above).
OR
- If the person has already been treated with an anti-HER2 drug.
It may also be given to people with:
- HER2-low (IHC 1+ or 2+/FISH negative) advanced or metastatic breast cancer, if the person has already been treated with chemotherapy.
- Metastatic breast cancer that is hormone receptor-positive and HER2-low (IHC 1+ or 2+/FISH negative) or HER2-ultralow (IHC 0 but with membrane staining), if the person has already been treated with an endocrine therapy.
Kinase inhibitors
HER2 is a type of protein known as a kinase. Kinases are proteins in cells that normally relay signals, such as telling the cell to grow. Drugs that block kinases are called kinase inhibitors.
Lapatinib is used to treat advanced breast cancer. It is typically given along with trastuzumab and the chemo drug capecitabine. This drug is a pill taken daily.
Neratinib is used to treat:
- Early-stage breast cancer after a person has been treated with trastuzumab for 1 year. Neratinib is usually given for 1 year.
- Metastatic disease when given along with the chemo drug capecitabine. It is typically used after at least 2 other anti-HER2 targeted drugs have been tried.
This drug is a pill taken daily.
Tucatinib is used to treat advanced breast cancer after at least one other anti-HER2 targeted drug has been tried. It is usually given along with trastuzumab and the chemo drug capecitabine.
This drug is taken as a pill, typically twice a day.
Side effects of HER2-targeted therapy
The side effects of HER2-targeted drugs are often mild, but some can be serious. Ask your cancer care team what to expect.
These drugs can harm or even cause the death of an unborn baby. Do not take them if you are pregnant. If you could become pregnant, use effective birth control during treatment.
Heart damage is a possible side effect of monoclonal antibodies and antibody-drug conjugates. This is usually temporary and improves once the drug is stopped. But it can lead to congestive heart failure in some people. The risk is higher when these drugs are combined with certain chemo medicines that also affect the heart, such as doxorubicin (Adriamycin) and epirubicin (Ellence).
Other factors that raise the risk include:
- Being older than 50
- Having excess body weight or obesity
- Having a history of heart problems
- Taking blood pressure medications
Because of this risk, your cancer care team will check your heart function before treatment. They will do this with an echocardiogram (ECHO) or MUGA scan and repeat these tests regularly during treatment. Tell your cancer care team right away if you have shortness of breath, a fast heartbeat, leg swelling, or severe fatigue.
Diarrhea can be a significant problem with lapatinib, neratinib, tucatinib, and the combination of pertuzumab with trastuzumab. Let your care team know about any changes in bowel habits as soon as they happen.
Hand-foot syndrome can happen with lapatinib and tucatinib. The hands and feet become sore, red, and may blister or peel.
Liver problems are a possible side effect of lapatinib, neratinib, and tucatinib. Your cancer care team will check your liver function with blood tests during treatment. Tell them right away if you notice itchy skin, yellowing of your skin or eyes, dark urine, or pain in the upper right side of your belly.
Serious lung disease has been reported with fam-trastuzumab deruxtecan (T-DXd, Enhertu). It can be life-threatening in some cases. Tell your cancer care team right away if you have a cough, wheezing, trouble breathing, or fever.
Targeted therapy for hormone receptor-positive breast cancer
About 3 out of 4 breast cancers are hormone receptor-positive (estrogen and/or progesterone). Treatment with hormone therapy is often helpful for these cancers.
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
CDK4/6 inhibitors 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 CDK4/6 inhibitors are approved to treat some hormone receptor-positive, HER2-negative breast cancers.
They are taken as pills, typically once or twice a day.
Advanced or metastatic breast cancer
These drugs can be used in a few ways to treat advanced breast cancer:
- Any of these drugs can be given with an aromatase inhibitor (AI) or fulvestrant in women with advanced breast cancer, regardless of menopausal status. Pre- or perimenopausal women must also stop their ovaries from making estrogen by taking medicine, such as an LHRH analog, or by having their ovaries surgically removed.
- Abemaciclib can also be used on its own in women with advanced breast cancer who have already been treated with hormone therapy and chemotherapy.
Early-stage breast cancer
Two of these drugs are used after surgery to lower the risk of early-stage breast cancer coming back:
- Abemaciclib can be given with tamoxifen or an AI for about 2 years in women with early-stage breast cancer that has spread to the lymph nodes and has a high risk of recurrence.
- Ribociclib can be given with an AI for about 3 years in women with stage II or stage III breast cancer at high risk of recurrence. Pre-menopausal women must also stop their ovaries from making estrogen by taking medicine or having their ovaries removed.
Common side effects
The most common side effects of CDK4/6 inhibitors include low blood cell counts and fatigue.
Less common side effects include nausea and vomiting, headache, mouth sores, hair loss, diarrhea, and liver inflammation or other liver problems. 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.
mTOR inhibitors
mTOR inhibitors block a protein in cells called mTOR. This protein normally helps cells grow and divide.
Everolimus (Afinitor) blocks mTOR, and it may also stop tumors from developing new blood vessels. This can help limit their growth. When used for treating breast cancer, it seems to help hormone therapy drugs work better.
This drug 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. It might also be used with fulvestrant, a hormone therapy drug.
Everolimus is taken as a pill, typically once a day.
Common side effects
Common side effects of everolimus include mouth sores, rash, diarrhea, nausea, feeling weak or tired, low blood counts, shortness of breath, and cough. Inflammation of the lung (pneumonitis) is a serious but less common side effect.
Everolimus can increase blood lipids (cholesterol and triglycerides) and blood sugars. Your blood will be tested regularly while you are taking it.
It can also increase your risk of serious infections, so your care team will watch you closely for infection.
PI3K inhibitors
PI3Ks are a family of proteins that send signals in cells that can affect cell growth. Drugs that target these proteins are known as PI3K inhibitors.
These targeted drugs block a form of the PI3K protein in cancer cells. This can help stop them from growing. They can be used to treat women with advanced hormone receptor-positive, HER2-negative breast cancer with a PIK3CA gene mutation (change) that has grown during or after treatment with hormone therapy.
The PIK3CA gene is the gene that tells the cell to make the PI3K protein. Your cancer care team will test your blood or tumor for this gene change before starting treatment with one of these drugs.
- Alpelisib is used along with the hormone drug fulvestrant.
- Inavolisib is used along with fulvestrant and the targeted drug palbociclib (see above).
These drugs are taken as pills, usually once a day.
Common side effects
Side effects of PI3K inhibitors can include high blood sugar levels, skin rash, mouth sores, diarrhea, nausea, fatigue, decreased appetite, and weight loss. These drugs can affect liver function in some cases, so your care team will regularly test your blood during treatment.
Some side effects can be more severe, and they might be more likely with one drug than with another. For example:
- Alpelisib is more likely to cause severe skin reactions, such as rashes with peeling and blistering, as well as serious lung inflammation (pneumonitis).
- Inavolisib is more likely to cause severe mouth sores.
- Both drugs might cause a person to have very high blood sugar levels or severe diarrhea.
AKT inhibitors
AKTs are proteins inside cells that help control how those cells grow and survive. Drugs that block these proteins are known as AKT inhibitors.
Capivasertib blocks forms of the AKT protein. This protein is part of a signaling pathway inside cells, including cancer cells, that can help them grow. Other proteins in this pathway include the PI3K and PTEN proteins.
This drug can be used along with the hormone drug fulvestrant to treat advanced hormone receptor-positive, HER2-negative breast cancer if:
- The cancer cells have changes in any of the PIK3CA, AKT1, or PTEN genes.
- The cancer has also grown during or after treatment with hormone therapy.
Your cancer care team will test your blood or tumor for these changes before starting this treatment.
This drug is taken as pills, typically twice a day for 4 days, followed by 3 days off each week.
Side effects
Side effects of capivasertib can include:
- High blood sugar levels: Your cancer care team will check your blood sugar levels before and during your treatment.
- Diarrhea (which may be severe): Tell your cancer care team right away if you start to have loose stools or diarrhea.
- Skin rash or other skin reactions: Very severe skin reactions, such as rashes with peeling and blistering, are possible. These should be reported to your care team.
Other possible side effects can include nausea, vomiting, mouth sores, and changes in certain blood tests.
Antibody-drug conjugates
An antibody-drug conjugate (ADC) is a monoclonal antibody joined to a chemotherapy medicine. The antibody acts like a homing device by attaching to a specific protein on cancer cells, bringing the chemo directly to them.
Some breast cancer cells have too much Trop-2, a type of protein that helps them grow and spread quickly. The monoclonal antibody in these ADCs attaches to the Trop-2 protein on breast cancer cells and brings the chemo directly to them.
These ADCs can be used to treat advanced hormone receptor-positive, HER2-negative breast cancer in people who have already received hormone therapy and chemotherapy.
These drugs are put into a vein (IV).
- Sacituzumab govitecan is typically given once a week for 2 weeks, followed by 1 week off, then restarted.
- Datopotamab deruxtecan is typically given once every 3 weeks.
Common side effects
Some common side effects of these drugs include nausea, vomiting, diarrhea, constipation, feeling tired, rash, loss of appetite, hair loss, low red blood cell counts, and belly pain.
Serious side effects
- Sacituzumab govitecan: Serious side effects of this drug can include very low white blood cell counts with an increased risk of infection, as well as severe diarrhea. An infusion reaction can happen at the time the drug is given. This is similar to an allergic reaction.
- Datopotamab deruxtecan: Serious side effects of this drug can include severe lung problems, eye problems, and mouth sores. An infusion reaction can happen at the time the drug is given.
You will get medicines before each treatment to lower the chances of vomiting and infusion reactions.
Targeted therapy for people with BRCA gene mutations
Some targeted therapy drugs can be used to treat breast cancer in people with BRCA gene mutations (changes). This includes people with:
- Germline BRCA mutations. This mutation is present in all cells of the body. A person is born with it.
- Somatic BRCA mutations. This mutation is present only in the cancer cells. A person develops it after birth.
If you have not already been tested, your cancer care team will do a blood test to find out if you have a BRCA mutation before starting one of these drugs.
PARP inhibitors
PARP proteins help repair damaged DNA inside cells. BRCA1 and BRCA2 genes also help repair DNA, but a change (mutation) in one of these genes can prevent that repair from happening properly.
PARP inhibitors block the PARP proteins. Because cancer cells with a BRCA mutation already struggle to repair damaged DNA, blocking PARP as well often causes these cancer cells to die.
These PARP inhibitors may be used to treat some people with BRCA mutations.
- Olaparib can be given after surgery to people with a BRCA mutation and early-stage HER2-negative breast cancer who were treated with chemotherapy before or after surgery and are at high risk of recurrence. It is typically taken for 1 year. It has been shown to help some people live longer.
- Olaparib and talazoparib can both be used to treat advanced or metastatic HER2-negative breast cancer in people with a BRCA mutation who have already received chemotherapy.
- For hormone receptor-positive, advanced or metastatic breast cancer, olaparib can also be used after prior hormone therapy.
These drugs are taken as pills once or twice a day.
Side effects
Side effects can include nausea, vomiting, diarrhea, fatigue, loss of appetite, taste changes, low red blood cell counts (anemia), low platelet counts, and low white blood cell counts.
Some people treated with a PARP inhibitor have developed a blood cancer, such as myelodysplastic syndrome or acute myeloid leukemia (AML), but this is rare.
Targeted therapy for triple-negative breast cancer
In triple-negative breast cancer (TNBC), the cancer cells do not have estrogen or progesterone receptors and they make very little or none of the HER2 protein.
Antibody-drug conjugates
An antibody-drug conjugate (ADC) is a monoclonal antibody joined to a chemotherapy medicine. The antibody acts like a homing device by attaching to a specific protein on cancer cells, bringing the chemo directly to them.
This ADC can be given alone or with pembrolizumab (Keytruda) as initial treatment for people with advanced TNBC.
Pembrolizumab may be put into a vein as the standard IV infusion or injected under the skin as a subcutaneous combination product with berahyaluronidase alfa (Keytruda Qlex). The combination is specifically for tumors that express a protein called PD-L1.
For people whose cancer has been treated with 2 or more prior systemic therapies, sacituzumab govitecan can also be used as a later-line treatment. This drug is put into a vein (IV) once a week for 2 weeks, followed by one week off, then restarted.
Common side effects
Some common side effects of this drug include nausea, vomiting, diarrhea, constipation, feeling tired, rash, loss of appetite, hair loss, low red blood cell counts, and belly pain.
Serious side effects
Serious side effects can include:
- Very low white blood cell counts, with an increased risk of infection
- Severe diarrhea
- Infusion reactions at the time the drug is given, similar to an allergic reaction
You will get medicines before each treatment to lower the chances of vomiting and infusion reactions.
This ADC can be given alone as initial treatment for people with advanced TNBC who are not candidates for PD-1/PD-L1 immunotherapy. It is given in a vein (IV) once every 3 weeks.
Common side effects
Some common side effects can include nausea, vomiting, diarrhea, constipation, feeling tired, rash, loss of appetite, hair loss, low red blood cell counts, and belly pain.
Serious side effects
Serious side effects can include:
- Severe lung problems, eye problems, and mouth sores
- Infusion reactions at the time the drug is given, similar to an allergic reaction
You will get medicines before each treatment to lower the chances of vomiting and infusion reactions.
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.
- Written by
- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
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Last Revised: July 9, 2026
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