Pertuzumab is a monoclonal antibody marketed by Genentech for the treatment of HER2-positive breast cancer, in combination with trastuzumab and docetaxel. The first of its class in a line of agents called "HER dimerization inhibitors". By binding to HER2, it inhibits the dimerization of HER2 with other HER receptors, which is hypothesized to result in slowed tumor growth. Early clinical trials of pertuzumab in prostate, breast, and ovarian cancers met with limited success. The combination of pertuzumab plus trastuzumab plus docetaxel, as compared with placebo plus trastuzumab plus docetaxel, when used as first-line treatment for HER2-positive metastatic breast cancer, significantly prolonged progression-free survival, with no increase in cardiac toxic effects in the randomized, double-blind, multinational, phase III CLEOPATRA trial.