Received: 1 March 2018
Accepted: 31 May 2018
First Online: 7 June 2018
Ethics approval and consent to participate
: Ethical approval for the study was obtained from the Institutional Review Board at Samsung Medical Center (No. 2016–08-192). Since the study was based on the retrospective analysis of existing administrative and clinical data, the requirement of obtaining informed consent was waived by the Institutional Review Board.
: The authors declare they have no competing interests.
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