Funding for this research was provided by:
National Natural Science Foundation of China (81672641)
Received: 24 September 2019
Accepted: 24 February 2020
First Online: 4 March 2020
Ethics approval and consent to participate
: We received permission to access the research data file in the SEER program from the National Cancer Institute, US (reference number 15218-Nov2017). Approval was waived by the local ethics committee, as SEER data is publicly available and de-identified.IK
: No individually identifiable data are presented.
: The authors declare that they have no competing interests.