Text and Data Mining valid from 2018-04-21
Received: 15 September 2017
Accepted: 10 April 2018
First Online: 21 April 2018
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: Because we obtain data from the SEER database with open access, we did not need to acquire patient consent or ethical review committee statement, but we were required to sign a Data-Use Agreement for the SEER 1973–2014 Research Data File to gain access to the SEER database.