The knowledge that Trastuzumab modulates the PI3K/AKT pathway leading to reduced cell growth and proliferation via binding to HER2 gives further mechanistic insight into the anti-cancer actions of the drug.16 Furthermore, Trastuzumab-resistant HER2-positive breast cancers can no longer be treated by modulating HER2 due to a mutation in the binding site. The gene discussed is ERBB2; the disease is breast cancer.