A drug used with other drugs to treat breast cancer that is HER2-positive. It is used in patients whose disease has spread to other parts of the body and has not been treated with anticancer drugs. It is also used before surgery in certain patients who are at high risk for their disease to recur (come back) or spread to other parts of the body. 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.