A humanized recombinant monoclonal antibody directed against the extracellular dimerization domain of the HER-2 tyrosine kinase receptor. Binding of the antibody to the dimerization domain of the HER-2 tyrosine kinase receptor protein directly inhibits the ability of the HER-2 tyrosine kinase receptor protein (the most common pairing partner) to dimerize with other HER tyrosine kinase receptor proteins; inhibiting receptor protein dimerization prevents the activation of HER signaling pathways, resulting in tumor cell apoptosis. or 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.