Funding for this research was provided by:
Postdoctoral Research Foundation of China (2019M650164)
Received: 23 July 2019
Accepted: 3 December 2019
First Online: 9 December 2019
Ethics approval and consent to participate
: Because patient data in the SEER database were de-identified, signed informed consent was waived for the present study.
: Not applicable.
: The authors declare that they have no competing interests.