Dr. Okumura has joined the board of surgery in Japan and the board of general thoracic surgery in Japan. He has also taken an active part in academic activities. He was the President of Japanese Association for Chest Surgery (JACS) from 2013 to 2017. He is the President of Japanese Association for Research on the Thymus (JART), as well as the member of European Society of Thoracic Surgeons (ESTS), European Association of Cardiothoracic Surgery (EACTS) and International Thymic Malignancy Interest Group (ITMIG). He has been an International councillor of ESTS from 2019.
Dr. Okumura specializes in surgery for lung cancer, thymic tumors, myasthenia gravis, and lung transplantation. He also focuses on basic research for oncology, immunology, and regenerative medicine.