Validation of the reporting of metachronous metastases after rectal cancer surgery in the Swedish ColoRectal Cancer Registry (SCRCR)

Abstract Introduction The SCRCR has a high coverage rate and good validity on variables regarding diagnosis and treatment of rectal cancer. As data from the SCRCR are used extensively in research and clinical quality evaluation with tumour recurrence as an important outcome, it is of essence to validate these variables. The aim of this study was to validate the registration of metachronous metastases of rectal cancer in the SCRCR. Method All patients registered with a diagnosis of rectal cancer between 2016 and 2017 who underwent abdominal resection of the rectal tumour were identified in the SCRCR. Medical charts were reviewed until end of follow-up June 30th, 2022. Patients with synchronous metastases, who were never tumour-free following surgery of the primary rectal tumour, were excluded. Result Of a total of 4211 patients registered with a diagnosis of rectal cancer, 2824 patients had an abdominal resection of the rectal tumour and available medical charts. Of these, 2754 patients (97.5%) were regarded as tumour free at some point following resection of the primary rectal tumour. Metachronous metastases were diagnosed in 591 of these patients (21.5%). In 499 patients (84.4%) the metachronous metastases were registered in the SCRCR. For an additional 53 patients registered with metachronous metastases in the SCRCR no metastases were identified in the medical records, which constitutes 9.6% of registered cases. Discussion There was a moderate underreporting of metachronous metastases in the SCRCR, why the procedures for reporting to the registry may need to be reviewed.