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 reduces the stimulation for cancer cells to divide. It may also allow the body's defences to fight better against the cancer cells.

Research trials have shown that 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. Around 1 in 4 women will have a large number of HER2 receptors on their cancer cells - this is known as being HER2-positive. When your breast cancer is diagnosed, the cells will be tested for HER2 protein.

In women who have early breast cancer and are HER2 positive, Herceptin may be used alongside, or after, other treatments. In women who have advanced breast cancer, Herceptin may be used to control the cancer for some time. You can discuss with your doctor whether it may be a suitable treatment for you.

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