A drug used with other drugs to treat breast cancer that is HER2-positive and has spread to other parts of the body. It is used in patients whose disease has not been treated with anticancer drugs. It is also being studied in the treatment of other types of cancer. Pertuzumab binds to HER2 on the surface of some cancer cells and may kill them. It is a type of monoclonal antibody. Also called Perjeta.