Data Collection

The data included in this study were extracted from the SEER 18 registries research database, and all enrolled patients were diagnosed with distal cholangiocarcinoma who received radical surgery between 2004 and 2015. The database collects cancer diagnosis, treatment, and survival data for ~30% of the United States population. Inclusion criteria were as follows: (1) patients classified as having “Bile Ducts Distal” according to “CS schema v0204+”; (2) patients older than 18 years at diagnosis; (3) patients with complete LN biopsy records; and (4) patients with survival time more than 1 mo. The exclusion criteria were as follows: (1) an unconfirmed diagnosis by histopathology; (2) an incomplete clinicopathological data; and (3) patients who had died of causes other than DCC, or an unknown cause. Ultimately, 676 patients with DCCs were enrolled in this study. The patients were randomly divided into a training set (n = 474) and a validation set (n = 202) at a ratio of 7:3. This study has been registered in Beijing Hospital, and the Beijing Hospital Medical Ethics Committee approved the study.

The following data were obtained: sex, age, race, year of diagnosis, histologic grade, SEER historic stage, histology, tumor size, AJCC TNM stage, T/N/M stage, ELNN, PLNN, LNR, and LODDS. The calculation formulas of LNR and LODDS are as follows: LNR = PLNN/ELNN; LODDS= log[(PLNN+0.05)/(ELNN-PLNN+0.05)]. Cancer-specific survival (CSS), defined as the date of diagnosis to the date of death from DCCs, was set as the end point of this study.