Performance of Different Comorbidity Indices in Predicting Mortality in Danish Pancreatic Cancer Patients.

Objective: Comorbidity indices are often used to adjust for confounding in epidemiological studies. However, the performance of comorbidity indices may vary depending on the clinical context. In the present study, we aimed to assess the incremental value of different comorbidity indices in predicting mortality in Danish pancreatic cancer patients. Methods: We conducted a nationwide cohort study of Danish patients diagnosed with pancreatic cancer from 2004 to 2022. Using national healthcare registries, we assessed comorbidities through five indices: Charlson, Elixhauser, van Walraven, Gagne, and Nordic Multimorbidity. We evaluated the added prognostic value of these indices using different lookback periods for predicting one-year mortality using logistic regression models with and without comorbidity scores to a basis model consisting of demographic characteristics, year of diagnosis, and tumour stage. Model performance was assessed by area under the receiver operating characteristic curve (AUC). We also conducted a sensitivity analysis restricting to patients undergoing surgery. Results: We included 10,413 patients diagnosed with pancreatic cancer during the study period. Tumour stage was the strongest predictor of mortality, increasing the AUC from 0.64 to 0.82. Adding any comorbidity index provided no meaningful improvement (AUC remained 0.82-0.83). Results were consistent across different lookback periods and in the analysis restricted to patients undergoing surgery. Conclusion: Comorbidity indices offer minimal additional prognostic value for mortality in pancreatic cancer beyond tumour stage and basic demographic factors.