Stephen Johnston is Professor of Breast Cancer Medicine, Consultant Medical Oncologist and Head of the Breast Unit at The Royal Marsden NHS Foundation Trust & Institute of Cancer Research, London.

He was appointed Head of Medical Oncology at The Royal Marsden in 2019, having previously been the first Director of the UK’s National Institute for Health and Care Research (NIHR) Biomedical Research Centre for Cancer at The Royal Marsden from 2006-12. He graduated in 1983 from Trinity College at the University of Cambridge, and in 1986 from the Medical School at the University of Newcastle upon Tyne. He trained in General Medicine at St Bartholomew's Hospital and Hammersmith Hospital in London, and subsequently in Medical Oncology at The Royal Marsden Hospital.He gained his PhD from the Institute of Cancer Research at the University of London, and took up his current position as Consultant Medical Oncologist in the Breast Unit at The Royal Marsden Hospital in 1997.

He has a specialist interest in the treatment of metastatic breast cancer, and his major research interests lie in understanding mechanisms of endocrine resistance in breast cancer. He is actively involved in facilitating the interface between basic and applied research, and has been Chief Investigator of several phase II / III trials of novel endocrine based therapeutic approaches in both advanced and early stage disease, including one of the large global adjuvant CDK 4/6 inhibitor studies in early breast cancer. He has published over 260 breast cancer related articles in peer-reviewed journals, and is a regular invited lecturer at national & international meetings.

He is a member of various scientific committees and international advisory boards, has served as Faculty Member at the American Society of Clinical Oncology and is currently on the Scientific Committee of the European Society for Medical Oncology.