Funding for this research was provided by:
Natural Science Foundation of Shandong Province (ZR2015HM066)
Received: 11 January 2018
Accepted: 7 May 2018
First Online: 11 May 2018
Ethics approval and consent to participate
: The project was approved by our Institutional Review Board (Shandong University), which waived the requirement for an individual patient consent because only routine patient data were used for this retrospective analysis.
: The authors declare that they have no competing interests.
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