Trastuzumab (also known as Herceptin®) is a treatment that may be given to some women with breast cancer. It is a type of drug known as a monoclonal antibody. It works by attaching to HER2 receptors (proteins) on the surface of breast cancer cells. This stops the cancer cells from dividing and growing. It may also allow the body’s defences to fight better against the cancer cells.

Herceptin® can reduce the chance of breast cancer coming back after initial treatment for early breast cancer. However, it is only effective for women whose breast cancer cells have a large number of the HER2 receptors on their surface. This is known as being HER2-positive. Around 1 in 5 women (20%) with breast cancer are HER2-positive. When your breast cancer is diagnosed, the cells will be tested for the HER2 protein.

In women who have early breast cancer and are HER2-positive, Herceptin® may be used alongside, or after, other treatments.

Side effects are usually mild but some women may have

• flu-like symptoms
• diarrhoea
• headaches
• an allergic reaction.

In some women, Herceptin® may cause damage to the heart muscle, which could lead to heart failure. If this happens the Herceptin® will be stopped. Usually, the effect on the heart is mild and reversible. Because the long term effects of any heart damage is not known, Herceptin® is not given to women who have serious heart problems. You can discuss with your doctor whether Herceptin® may be a suitable treatment for you.

For more detailed information about Herceptin®, including side effects, please see our section on Trastuzumab (Herceptin®).