A drug used with other drugs to treat breast cancer that is HER2 positive. It is used in patients whose cancer has spread to other parts of the body and has not been treated with other anticancer drugs. It is also used before surgery in certain patients and after surgery in some patients who are at high risk for their cancer to recur (come back). It is also being studied in the treatment of other types of cancer. Pertuzumab binds to a protein called HER2, which is found on some cancer cells. Blocking this protein may help kill cancer cells. Pertuzumab is a type of monoclonal antibody. Also called Perjeta.