Funding for this research was provided by:
National Natural Science Foundation of China (81502332)
Article History
Received: 2 April 2020
Accepted: 3 July 2020
First Online: 3 September 2020
Compliance with ethical standards
: All data were extracted from the SEER database, and no additional Institutional Review Board approval was needed for this study.
: The authors declare that they have no conflict of interest.