The Korean National Health Insurance Service (NHIS) is a mandatory health insurance system for all citizens, including detailed data on demographics, lifestyle behaviors, outpatient department visits, hospitalizations, pharmacological prescriptions, surgical and adjuvant treatments, and laboratory examinations [6]. All citizens aged 40 years or older are eligible for a biannual screening that involves self-reported questionnaires regarding medical history, behavioral characteristics, anthropometric measurements, and laboratory findings [7]. In the Korean NHIS, critical codes for cancer were implemented in 2004. Therefore, patients with cancer are offered additional critical condition codes that are adopted only when a diagnosis of cancer is confirmed [8]. These codes provide reimbursement benefits for cancer-associated management costs based on the household incomes of patients. The diagnosis of CRC was made within the dataset by the attending physicians who recorded a primary diagnosis according to the International Classification of Diseases, Tenth Revision (ICD-10) codes.

This population-based, retrospective cohort study utilized data from the Korean NHIS. The inclusion criteria were patients with new-onset CRC who survived at least 5 years and had available demographic characteristics, follow-up information, and clinical data. Patients with CVD before the index date, defined as the date of 5-year survival for each participant, and those with missing values for covariates were excluded. All patients were followed up from the index date to the date of CVD, death, or December 31, 2018 (see Figure S1 in a supplementary file). This study was approved by the Institutional Review Board of Seoul National University (approval number E-2004-191-1119). The requirement for informed consent was waived by the review board, as the NHIS database is anonymized by strict confidentiality guidelines.

Among the 33,483 patients who were diagnosed with CRC (ICD-10 codes, C17–C21) and received health examinations, we excluded 5869 patients with CRC before 2006 to restrict the study population to only those patients with newly diagnosed CRC. To reconcile the starting point of observation and detect new-onset CVD, we excluded 5905 patients who had CVD prior to the index date. In addition, 1056 patients who had missing values for covariates were excluded. The final study population included 20,653 patients with CRC who survived ≥5 years after the initial diagnosis.

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