Trastuzumab is an antibody drug that targets HER2-positive cancer cells.

Trastuzumab attaches to the HER2 protein on the surface of HER2-positive breast cancer cells, helping to slow or stop their growth.

For women with HER2-positive early breast cancer, chemotherapy plus trastuzumab cuts the risk of recurrence in half compared to chemotherapy alone.

Trastuzumab is given through an IV into a vein or by injection under the skin every 3 weeks for one year.

Treatment with trastuzumab may begin before breast cancer surgery, which is called neoadjuvant therapy, or after surgery, called adjuvant therapy.

Possible side effects of trastuzumab include headache, fever and chills.

More serious but less common risks include heart problems and possible congestive heart failure.

The risk of heart problems is higher when trastuzumab is combined with some chemotherapy drugs, so these combinations are avoided. The risk of heart problems may also be higher for women over 60 and for those who already have heart problems.

For most people who develop a heart problem while taking trastuzumab, the condition improves after they stop taking it. For a few, these issues may be permanent. Try not to worry, your heart will be checked before and during treatment to make sure any potential problems are avoided or caught early.

The Food and Drug Administration, or FDA, has approved several biosimilar forms of trastuzumab for HER2-positive breast cancer. A biosimilar drug is a generic-like drug that’s very similar to a brand name drug that contains biologics. The FDA-approved biosimilar forms of trastuzumab are safe and effective treatments for early HER2-positive breast cancers.

For more information, visit the HER2-Targeted Therapies page within the Treatment section of komen.org.

Trastuzumab is also used to treat HER2-positive metastatic breast cancer. For more information, see the Living with Metastatic Breast Cancer chapter of this tool.