Trastuzumab is standard of care in the treatment of human epidermal growth 
factor receptor (HER)-2⁺ early and advanced breast cancer. Recently, it has been 
approved for the treatment of HER-2⁺ advanced gastric cancer. Trastuzumab is an 
IgG1 humanized monoclonal antibody administered by intravenous infusion on a 
weekly or three weekly schedule. In all registered indications, trastuzumab is 
almost always given in combination with chemotherapy. In hormonal 
receptor-positive breast cancer in postmenopausal women, trastuzumab can be 
combined with an aromatase inhibitor. Main toxicity is reduction in the left 
ventricular ejection fraction, which in a minority of patients can become 
symptomatic, but in many patients is at least partly reversible. Long-term 
safety needs to be further determined.