Context
Trastuzumab (HerceptinR) is a recombinant monoclonal antibody that binds to the transmembrane growth factor receptor Her-2, and is one of the first successful examples of targeted therapy in the treatment of cancer. However, in about 60% of patients, who receive HerceptinR alone as first-line therapy, no objective responses are observed, even if the tumour has an intensive Her-2 positivity. The authors hypothesized that the high failure rate of treating patients with HerceptinR could result from different Her-2 expression between a primary tumour and its metastases. Since HerceptinR works by targeting the metastases, if at least some of the multiple metastases of a Her-2-positive primary breast cancer do not express Her-2, then HerceptinR would most likely not affect the course of the disease.