Impact of 10 Different Prior Cancer History on Survival of Patients Who Underwent Surgery for Second Primary Colorectal Cancer: a Population-based Cohort Study

In this study, the investigators collected data with the SEER\*Stat software version 8.4.1 (accession number: 20377-Nov2021). The patients with confirmed diagnoses of CRC (site code C18.0-20.9 and C26.0) between 2004 and 2013 were retrieved from the Surveillance, Epidemiology, and End Results (SEER) database. Due to the significant disparity in the number of cancer survivors with various prior cancer types among newly diagnosed CRC patients, the investigators utilized the International Classification of Diseases for Oncology, 3rd edition (ICD-O-3) Site Recode to identify 10 common previous cancer sites, including the colorectum, prostate, breast, uterus, bladder, skin, lung, kidney, thyroid, and stomach. CRC patients with a prior history of cancer originated from one of the 10 sites and surgical CRC patients without a prior history of cancer were enrolled in this study. The exclusion criteria were as follows: (1) Patients with more than one cancer in the past; (2) The patient's age at diagnosis was \<18 years old; (3) Patients with incomplete survival data and follow-up information; (4) Patients only had autopsy or death certificate records. The primary outcomes of this study were overall survival (OS) and cancer-specific survival (CSS). OS was defined as the time from diagnosis to date of death（patients who were still alive at the end of follow-up were considered as censored data. CSS was defined as the time from diagnosis to date of death caused by CRC (patients who deaths from other causes or still alive at the end of follow-up were considered as censored data). The investigators set December 31, 2018, as the cut-off date for follow-up to ensure that all included cases (diagnosed in 2004-2013) were followed for at least 5 years. Based on prior cancer history, the surgical cases were categorized into two groups: 'Non-prior cancer history' and 'Prior cancer history.' The 'Prior cancer history' group was further subcategorized by the type of prior cancer, includin