Pertuzumab is a drug designed to be used in combination with trastuzumab to block the HER2 growth factor, which is the cause of about a third of all breast cancers. The experimental drug has been developed specifically to prevent the HER2 receptor to mate with other HER receptors (EGFR/HER1, HER3 and HER4): by preventing the coupling of receptors, it is thought that it blocks cell signalling, inhibiting cell growth or by determining the death of diseased cells. It is necessary a study of HER2 signal transduction pathway with the goal of providing personalized medicines to patients with HER2-positive breast cancer. With these results, it will soon be possible to be able to improve the current standard of care, consisting of trastuzumab plus chemotherapy, in order to help patients with this advanced form of cancer. It is believed that the mechanisms of action of pertuzumab and Herceptin are complementary to each other: both bind to the HER2 receptor but on different areas. Many of the patients with this type of metastatic cancer at some point stop responding to trastuzumab; this is the reason why it is unsettling the fact that there is a drug that in addition to this it increases so much progression-free survival. Moreover, the addition of the drug to the combination therapy resulted in a significant decrease of the tumors (i.e. at least one third) in 80,2% of cases, compared with 69,3% of the control group. Although data on the rate of overall survival are not yet available as it has not passed enough time since the end of the study because the statistical analysis is truly consistent, CLEOPATRA (randomized study in more centers) has seen 69 deaths among 402 patients treated with three drugs, compared with 96 in the group that received placebo. The arrival of pertuzumab before and then trastuzumab, biological therapy is making great strides in treating this type of cancer that previously had a very complicated prognosis.