HER2/neu is a protein involved in the growth of breast cancer cells. Breast cancer cells that have several copies of the HER2/neu protein on their cell surface than normal form a type of breast cancer that is called HER2 amplified. It is thought to be more aggressive than breast cancers that do not have more copies of HER2 protein than normal, but usually responds very well to medication that specifically homes in and targets the HER2 protein on the cancer cells, what is called “targeted therapy”. This medication includes trastuzumab (Herceptin) and pertuzumab (Perjeta). These medications are usually combined with other chemotherapy agents. This anti-HER2 medication is sometimes given prior to surgery to shrink the tumor, allowing a smaller surgery, in what is called “neoadjuvant chemotherapy”.
See also: What is breast cancer?