Herceptin® (trastuzumab) is a type of drug, called a monoclonal antibody. It works differently from chemotherapy. It targets and 'neutralises' the HER2 protein, that is found in some types of breast cancer. So Herceptin only works for breast cancers that are HER2 positive.

HER2 positive breast cancers have higher than normal amounts of (overexpress) HER2 protein. These breast cancers are more likely to come back or spread to other parts of the body than breast cancers that are HER2 negative. Most breast cancers are HER2 negative but up to 1 in 4 are HER2 positive.

Until recently, Herceptin has only been used to treat women with HER2 positive breast cancer, that had spread to other parts of the body (advanced cancer).

Because of Herceptin's effectiveness in treating advanced breast cancer, three large clinical trials looked at whether Herceptin would help women with early breast cancer, by reducing the risk of it coming back after treatment.

In the trials, women with HER2 positive breast cancers, had surgery and then chemotherapy, with or without Herceptin.

Early results from all three trials show very similar results. The women who had Herceptin had their risk of the cancer coming back halved, compared with the women who had chemotherapy alone.

These figures are very encouraging, but there are some important things to remember:

• Herceptin only works if the cancer is HER2 positive, and so is suitable for only 20-25% of patients
• These are early results, and could change as the women in the trials are followed up for a longer time
• Herceptin has fewer side effects than chemotherapy but it does have side effects, and can cause heart damage in some people
• The long-term effects of taking Herceptin for women with early breast cancer are not yet known

It's now recommended that all women in the UK, with newly diagnosed breast cancer, are tested for HER2. Your specialist will be able to tell you whether you have a HER2 positive breast cancer and if Herceptin may be helpful to you.

Current guidance from the National Institute of Health and Clinical Excellence suggests that women should be considered for treatment with Herceptin if they are HER2 positive, the tumour is larger than 1cm and the cancer had spread to the lymph nodes under the arm.

The full guideline can be read on the NICE website.