Trastuzumab attaches to the HER2 protein, allowing the chemotherapy emtansine to enter the cancer cell. Once inside the cell, the emtansine becomes active and kills the cell. This way, ado-trastuzumab emtansine causes cancer cells to die, while leaving healthy cells unharmed.

Common side effects of ado-trastuzumab emtansine include

• bone and joint pain
• diarrhea or constipation
• liver problems
• low platelet count, which may result in bruising
• low potassium levels
• low red blood cell count, which may result in fatigue and weakness
• nausea or stomach ache
• neuropathy, tingling or numbness in the hands or feet

Some people who take ado-trastuzumab emtansine develop a low white blood count, which may put you at risk for infection. Call your doctor right away if you show any symptoms of infection, such as a fever with chills.

If you have serious side effects, your doctor may stop treatment for a time or switch you to another treatment.

Before starting ado-trastuzumab emtansine, tell your doctor about any history of heart or lung problems as well as any medicines you are taking, including vitamins, herbal supplements and over-the-counter medicines. You should not become pregnant while taking ado-trastuzumab emtansine.

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.