Retrospective Analysis of SEER Patients

We retrieved patients from the SEER database (2006–2017). Patients between 2004 and 2005 were not included in the study because of the missing chemotherapy data in the SEER database. The inclusion criteria were as follows: (1) positive histology; (2) underwent radical surgery; (3) definite tumor stage (T-category) and nodal stage (N-category), according to the 8th edition of the American Joint Committee on Cancer (AJCC) criteria; (4) first primary tumor; (5) at least one regional lymph node dissection based on pathologic evidence; (6) treatment with/without preoperative radiotherapy and/or chemotherapy; and (7) no distant metastasis. The exclusion criteria were: (1) under 18 years old; (2) unavailable follow-up data; (3) unknown cause of death. We retrieved baseline characteristics, including the year of diagnosis, race, age, sex, histology, grade, marital status, T-category and N-category. The data from all subjects from the SEER database was obtained legally.