Validation of a register-based algorithm for recurrence in rectal cancer.

INTRODUCTION: Colorectal cancer is the third most common type of cancer worldwide. Recurrence is an important end-point in colorectal cancer research. This study aimed to validate a previously developed algorithm to determine recurrence after surgery for rectal cancer. METHODS: Information about a cohort of 500 patients with rectal cancer was retrieved from the Danish Civil Registration System, the Danish National Patient Register and the Danish National Pathology Register. Patients with an ICD-to code for metastatic disease, chemotherapy or SNOMED code suggesting metastasis were identified as having recurrence. In a previous study, medical records of the same cohort had been reviewed to identify recurrence. Recurrence identified by the algorithm was compared with the previously retrieved information from the medical records using Kappa statistics. The sensitivity and specificity of the algorithm were determined. RESULTS: Of the 500 patients, 393 were included in the validation analysis. Kappa statistics showed good concordance with a Kappa value (95% confidence interval) of 0.80 (0.72-0.88). The sensitivity and specificity of the algorithm were 88% (77-95%) and 96% (93-98%), respectively. CONCLUSIONS: The study showed good concordance between the algorithm and medical record information. The algorithm makes it possible to perform large register-based studies of recurrence and disease-free survival in colorectal cancer patients without the need for evaluation of medical records.