Received: 1 February 2019
Accepted: 30 September 2019
First Online: 6 November 2019
Ethics approval and consent to participate
: This retrospective study was approved by the Institutional Review Board (IRB) of the National Cancer Center Hospital (IRB code: 2017–437). It was determined to be a retrospective analysis of de-identified data, and was determined to be exempt from requiring written informed consent.
: Not applicable.
: The authors declare that they have no competing interests.