Dr Karen Breen is a consultant haematologist with a specialist interest in thrombosis. She completed her undergraduate training at Trinity College, Dublin, and pursued postgraduate training in haematology in Ireland before moving to the UK to conduct research leading to an MD.

Dr Breen is a member of the Royal College of Physicians of Ireland and the Royal College of Pathologists, UK. She is currently involved in several clinical trials and translational research in antiphospholipid syndrome and has authored and co-authored numerous publications on thromboembolic disease.

At Guys and St. Thomas' Foundation Trust, Dr Breen leads the acute management of thrombosis and anticoagulation. She is also a member of the Trust Thromboprophylaxis and Thrombosis Committee. Her expertise includes the management of conditions such as deep vein thrombosis, pulmonary embolism, and antiphospholipid syndrome.

Dr Breen has authored several research papers and regularly lectures both nationally and internationally. She was appointed to her current role in 2010 and continues to contribute significantly to the field of haematology through her clinical and research efforts.