Data on CRC patients with synchronous liver metastasis (LM) were derived from the US Surveillance, Epidemiology, and End Results (SEER) and a Chinese registry (from two Chinese tertiary centers: The Second Affiliated Hospital of Harbin Medical University and National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences \& Peking Union Medical College) between January 2010 and December 2017. Individual level data on patients with incident CRC were consecutively collected in both registries. The primary tumor site was divided into three subsites according to International Classification of Diseases for Oncology (ICD-O-3) topography codes: proximal colon (C18.0, C18.1, C18.2, C18.3 and C18.4), distal colon (C18.5, C18.6, C18.7) and rectum (C19.9 and C20.9). The synchronous LM were identified by imaging or histopathological examinations. Synchronous LM refers to liver lesions found within 6 months after the diagnosis of primary CRC. Patients were excluded if they did not undergo surgery for CRC, did not have data on number of LNs retrieved and their survival status was unknown.
