The validity of registered synchronous peritoneal metastases from colorectal cancer in the Danish medical registries

Introduction: Treatment options for peritoneal metastases (PM) from colorectal cancer (CRC) have increased, their efficiency should be monitored. For this purpose, register-based data on PM can be used, if valid. Purpose: We aimed to evaluate the completeness and positive predictive value (PPV) of synchronous peritoneal metastases (S-PM) registered among CRC patients in the Danish National Patient Register (DNPR) and/or the Danish National Pathology Register (the DNPatR) using the Danish Colorectal Cancer Group database (DCCG) as a reference. Patients and Methods: We identified Danish patients with newly diagnosed primary CRC in the DCCG during 2014–2015. S-PM were routinely registered in the DCCG. We excluded patients with non-CRC cancers and identified S-PM using all three registries. We estimated the completeness and the PPVof registered S-PM in the DNPR, the DNPatR and the DNPR and/or the DNPatR (DNPR/DNPatR) in combination using the DCCG as the reference. We stratified by age, gender, WHO performance status, tumour location and distant metastases to liver and/or lungs. Results: We identified 9142 patients with CRC in DCCG. In DCCG, 366 patients were registered with S-PM, among whom 213 in DCCG only, whereas 153 in DCCG and in at least one of DNPR and/or DNPatR. In DNPR/DNPatR, S-PM was registered with a completeness of 42% [95% CI: 37–47] and a PPV of 60% [95% CI: 54–66]. In the DNPR only, the completeness was 32% [95% CI: 27–37] and the PPV 57% [95% CI: 50– 64]. The completeness in the DNPatR was 19% [95% CI: 15–23] and the PPV was 76% [95% CI: 68–85]. In the DNPR/DNPatR patients aged <60 years (57% [95% CI: 46–69]), patients with WHO performance status 0 (46% [95% CI: 37–54]) and patients with no distant metastases (58% [95% CI: 50–65]) were registered with a higher completeness. Conclusion: Our algorithm demonstrates that the DNPR/DNPatR captures less than half of CRC patients with S-PM. Potential candidates for curative treatment options are registered with a higher completeness. Clinicians should be encouraged to register the presence of S-PM to increase the validity of register-based S-PM data.