Trastuzumab is an antibody drug specially made to target HER2-positive cancer cells.

Trastuzumab attaches to the HER2 protein on the surface of HER2-positive breast cancer cells. This can 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 by vein (through an IV) or by injection under the skin every 3 weeks for one year.

Treatment with trastuzumab may begin before breast cancer surgery (called neoadjuvant therapy) or after surgery (called adjuvant therapy).

There are some risks related to trastuzumab. Trastuzumab is linked to 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 stopping trastuzumab. For a few, it may be permanent. A person treated with trastuzumab has a heart exam before treatment begins and regular heart monitoring during treatment.

The FDA has approved several biosimilar forms of trastuzumab for HER2-positive breast cancer. A biosimilar drug is a “generic-like” drug that is very similar to a brand name drug that contains biologics.

To be approved by the FDA, a biosimilar must work the same way as the brand name drug and it must:

• Be as safe when used alone or in combination with other treatments
• Be as effective when used alone or in combination with other treatments
• Have similar side effects (they can’t be different from those of the original drug)
• Have the same form as the original drug (for example, if the original drug is given by vein (through an IV) the biosimilar must also be given by vein)

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

Ado-trastuzumab emtansine (T-DM1 or Kadcyla) is an antibody-drug conjugate. It consists of trastuzumab along with a chemotherapy called DM1. Combining these drugs allows the targeted delivery of chemotherapy to HER2-positive cancer cells.

Ado-trastuzumab emtansine is used to treat some women with HER2-positive early breast cancer who have cancer remaining in their breast or lymph nodes after neoadjuvant therapy. The use of ado-trastuzumab emtansine in these women can reduce the risk of breast cancer recurrence and breast cancer death by 50 percent compared to treatment with trastuzumab.

T-DM1 is given through an IV every 3 weeks for 14 cycles. Treatment begins after breast surgery.

Possible side effects of ado-trastuzumab emtansine include nausea, fatigue, muscle and joint pain, low platelet counts, headache and constipation. It can also cause liver and heart problems. Because ado-trastuzumab emtansine contains trastuzumab, it can cause congestive heart failure, a serious heart condition.

Ado-trastuzumab emtansine is also used to treat HER2-positive metastatic breast cancer.

For more information on these drugs, see the Living with Metastatic Breast Cancer section in this tool.