Article History
Received: 29 June 2020
Accepted: 7 October 2020
First Online: 17 October 2020
Ethics approval and consent to participate
: This study was deemed exempt by the Ethics Committee of Peking Union Medical College Hospital, Beijing, China, since the data we used were obtained from the publicly available SEER database.
: No conflict.
: The authors declare that they have no competing interest.