Case-mix adjustment for between-hospital comparisons in oesophageal and gastric cancer surgery

Clinical and pathological outcomes of oesophagogastric cancer surgery are used for benchmarking hospital performance. The extent to which case-mix adjustment is required for valid hospital comparisons is unknown. This study aimed to develop distinct case-mix adjustment models for multiple outcomes of oesophageal and gastric cancer surgery, and to assess the impact of case-mix adjustment on between-hospital comparisons.

We included all patients who underwent oesophagogastric cancer resections in the Netherlands between 2017 and 2022. We developed distinct case-mix adjustment models for ten outcomes. Model performance was evaluated with the area-under-the-receiving-operator-curve (AUC) and pseudo-R-squared, representing how strongly case-mix factors predict the outcomes. We used the Wald χ² test to assess relative predictor importance per model. The impact of case-mix adjustment on between-hospital comparisons on outcome was quantified using unadjusted and adjusted observed/expected ratios.

In total, 4354 oesophageal cancer patients and 2109 gastric cancer patients were included. The most informative predictors in the models for oesophageal cancer were ASA-score, salvage surgery, peripheral vascular disease/aortic aneurysm, chronic lung disease, and tumour histology. For gastric cancer these were age, preoperative weight loss, tumour location, and clinical M-category. All case-mix models showed low to moderate performance, with AUCs ranging between 0.58 and 0.73 and between 0.58 and 0.74 for oesophageal and gastric cancer, respectively. Overall, case-mix adjustment had a limited impact on between-hospital comparisons, but more pronounced for 30-day mortality, failure-to-cure and failure-to-rescue.

Given low to moderate model performance and the limited impact on between-hospital comparisons, case-mix adjustment may not always be necessary for valid benchmarking on outcomes in oesophagogastric cancer surgery.