Fatima Cardoso, MD, from the Champalimaud Clinical Cancer Centre, Lisbon, Portugal talks to us about a session at the 2017 European Society for Medical Oncology (ESMO) conference in Madrid, Spain which debated whether the practice of treating breast cancer patients with trastuzumab as a single agent should be changed following the results of the APHINITY trial (NCT01358877). This study found that a combination of chemotherapy, trastuzumab and pertuzumab could increase survival in HER2-positive patients. Dr Cardoso explains the structure of the debate and discusses the conclusions drawn.