Visiting The Royal Marsden is suspended

Coronavirus latest: Please kindly note that whilst lockdown restrictions are beginning to ease, visiting is still suspended.  The hospital remains open and we are still delivering treatment to our patients. Please see more information here about how we are keeping everyone safe.

Professor Mary O'Brien

Consultant Medical Oncologist MD FRCP

Specialism: Breast, Lung

Available at: Cavendish, Sutton

Special interests:

  • Chemotherapy for lung cancer
  • Biological therapy for lung cancer
  • Immunotherapy for lung cancer
  • Chemotherapy for breast cancer
  • Endocrine therapy for breast cancer
  • Immunotherapy for breast cancer


Professor Mary O’Brien is an experienced medical oncologist at the RMT and Professor of Practice Imperial College London. Professor O’Brien treats breast and lung cancer, mesothelioma and other rare thoracic tumours. She is currently Head of the Lung Unit and chair of the LORD subgroup of the lung cancer NCRI clinical studies group. She is also past chair of the SWL lung TWG, EORTC lung cancer group and former subeditor of the lung section of the European Journal of Cancer.

Professor O’Brien has a long history of clinical research, with over 200 original publications and many reference articles. She was involved in the development of immunotherapy and with the major practice changing trial Keynote 024. She is international chief investigator for the PEARLS trial in lung cancer, which could lead to another paradigm shift in lung cancer treatment when reported over the next few years.

Professor O’Brien aims to give a holistic approach to the treatment of her patients based on compassion, understanding and up to date knowledge.

Clinical units