http://www.cancerbacup.org.uk/QAs/Tr...s/QAs/83663880
"The current research shows that women with the BRAC1 and BRAC2 mutations are less likely to be HER2 positive than women who have what is known as sporadic breast cancer (breast cancer that is not thought to be caused by a faulty gene). Only about 1 in 50 women with a BRCA gene mutation is likely to have an HER2 positive tumour, whereas between 1 in 3 to 1 in 5 women with sporadic breast cancer will have high HER2 levels. So Herceptin is less likely to be helpful for those women who have a BRCA1 or BRCA2 gene change."