Herceptin® (trastuzumab) belongs to a new group of anti-cancer drugs called monoclonal antibodies. It works best in women whose cancer has high levels of the HER2 protein and appears to have little effect in breast cancers that don't. So it is only used for women with cancers which have high levels of HER2 protein (HER2 positive).

The current research shows that women with the BRCA1 and BRCA2 mutations are less likely to be HER2 positive than women who have sporadic breast cancer (breast cancer that is not caused by inheriting a faulty gene). Between 1 in 4 to 1 in 5 women with sporadic breast cancer have high HER2 levels. But, only about 1 in 50 women with a BRCA gene mutation have a HER2 positive tumour. So Herceptin is less likely to be helpful for those women who have a BRCA1 or BRCA2 gene change.