Received: 30 January 2020
Accepted: 4 May 2020
First Online: 13 May 2020
Ethics approval and consent to participate
: The study protocol complied with the principles of the Declaration of Helsinki and the Code of Ethics of the World Medical Association for experiments that involve humans. The study protocol was approved by the Ethics Committee of the Shinshu University School of Medicine, Matsumoto, Japan (#4274). The dataset, which contained individual data of patients and institutions, had been anonymised prior to the analysis, and the Institutional Review Board decided that individual informed consent was not needed for the retrospective study.
: Not applicable.
: K Mochizuki has received personal fees from Asahi Kasei Pharma Co. and Toray Medical Co., which were unrelated to the present study. All other authors declare that they have no conflicts of interest.