The medicine trastuzumab (Herceptin and biosimilars) is the most common medicine used to treat HER2-positive breast cancer. It is a monoclonal antibody, a medicine made in a lab that attacks a specific protein produced on the outside of a cell. It falls in a class of medicines called targeted therapies.

Research shows people with HER2-positive breast cancer treated with trastuzumab along with chemotherapy are likely to live longer than those with HER2-positive disease who receive chemotherapy alone. Treatment with trastuzumab and chemotherapy also cuts the risk of recurrence, or return of the cancer, in half.

How trastuzumab works

Trastuzumab works by attaching to HER2 proteins and blocking the signals that tell cells to multiply too quickly, causing cancer.

Who gets trastuzumab

Trastuzumab is a standard treatment for both early-stage and metastatic HER2-positive breast cancer. It is also a standard therapy for HER2-positive inflammatory breast cancer.

If the cancer you have is both hormone receptor positive and HER2 positive, you are likely to receive targeted treatments for both types of breast cancer.

How trastuzumab is given

Trastuzumab can be given by vein or by injection.

Trastuzumab given by vein uses a needle or a port to drip medicine directly into a vein in a process called infusion. The first infusion may last 90 minutes or longer, after which infusions usually take around 30 minutes. The dose is based on how much you weigh.

Trastuzumab given by injection is delivered by inserting a needle under the skin, usually in the thigh, without needing to access a vein. It takes about 5 minutes. The dose does not change based on your weight. This treatment is called trastuzumab and hyaluronidase-oyst (Herceptin Hylecta).

In early-stage disease, you may receive trastuzumab or trastuzumab and hyaluronidase-oyst either before or after surgery. The medicine is given either once a week or once every 3 weeks for a year. It is given with chemotherapy at the start of treatment, then may be given alone for an extended period of time. If you have a high risk of recurrence, you may also receive pertuzumab (Perjeta), another HER2-targeting treatment, either before or after surgery. Pertuzumab can be given with trastuzumab in a single injection called pertuzumab, trastuzumab, and hyaluronidase-zzxf (Phesgo).

Common combinations that include trastuzumab are:

One common plan is to take chemotherapy alone for several cycles, and then take taxane chemotherapy along with trastuzumab. When you finish the taxane, your team will continue to give you trastuzumab until you finish about a year of treatment. Your providers may also give you all your chemotherapy first and then start trastuzumab. Ask why they suggest one option over the other.

When given before surgery, trastuzumab and medicines given with it help to shrink large tumors. In some cases, this neoadjuvant treatment makes it possible to have a lumpectomy instead of a mastectomy.

In metastatic breast cancer, trastuzumab can be given alone on an ongoing basis or with pertuzumab and chemotherapy. Ask your team to explain why they recommend a certain treatment or combination.

You and your doctor will discuss the best treatments for your situation.

Side effects and things to remember

In general, trastuzumab is less likely than chemotherapy to cause serious side effects that could make you need to stop treatment. Some people have flu-like symptoms after starting trastuzumab. The most common side effects include

If you are also receiving chemotherapy, you may also have chemotherapy side effects.

Heart problems are a rare but serious possible side effect of trastuzumab. The idea of heart issues can be scary, but research shows most heart problems caused by trastuzumab are not permanent or long-term. Though it’s unlikely you’ll have serious heart problems while taking trastuzumab, it’s important your doctor closely monitor your heart health while you take this medicine.

Before you start trastuzumab and throughout treatment, you should get an echocardiogram (sometimes called an echo) to look at your heart health. If your first echo suggests you have heart problems, trastuzumab may not be the right treatment for you. Talk with your healthcare team about other options.

Before starting trastuzumab, tell your doctor about any medicines you are taking, including vitamins, herbal supplements, and over-the-counter medicines. Trastuzumab may be dangerous to a fetus if taken while pregnant. You should not take it if you are pregnant or breastfeeding, and you should take steps to avoid getting pregnant while on trastuzumab.

Your doctor, pharmacist or nurse can help you manage your side effects. You can also go to our section on side effects for more information.



Reviewed and updated: March 25, 2021

Reviewed by: Tiffany Avery MD MPH


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Living Beyond Breast Cancer is a national nonprofit organization that seeks to create a world that understands there is more than one way to have breast cancer. To fulfill its mission of providing trusted information and a community of support to those impacted by the disease, Living Beyond Breast Cancer offers on-demand emotional, practical, and evidence-based content. For over 30 years, the organization has remained committed to creating a culture of acceptance — where sharing the diversity of the lived experience of breast cancer fosters self-advocacy and hope. For more information, learn more about our programs and services.