Outcome variation and the role of caseload in certified colorectal cancer centers – a retrospective cohort analysis of 90 000 cases

Background: Studies have shown that surgical treatment of colorectal carcinomas in certified centers leads to improved outcomes. However, there were considerable fluctuations in outcome parameters. It has not yet been examined whether this variability is due to continuous differences between hospitals or variability within a hospital over time. Materials and Methods: In this retrospective observational cohort study, administrative quality assurance data of 153 German-certified colorectal cancer centers between 2010 and 2019 were analyzed. Six outcome quality indicators (QI) were studied: 30-day postoperative mortality rate (POM), surgical site infection rate (SSI), anastomotic insufficiency rate (AI), and revision surgery rate (RS). AI and RS were also analyzed for colon (C) and rectal cancer operations (R). Variability was analyzed by funnel plots with 95% and 99% control limits and modified Cleveland dot plots. Results: In the 153 centers 90,082 patients with colon cancer and 47,623 patients with rectal cancer were treated. Average QI scores were 2.7% POM, 6.2% SSI, 4.8% AI-C, 8.5% AI-R, 9.1% RS-C, and 9.8% RS-R. The funnel plots revealed that for every QI about 10.1% of hospitals lay above the upper 99% and about 8.7% below the lower 99% control limit. In POM, SSI, and AI-R, a significant negative correlation with the average annual caseload was observed. Conclusion: The analysis showed high variability in outcome quality between and within the certified colorectal cancer centers. Only a small number of hospitals had a high performance on all six quality indicators, suggesting that significant quality variation exists even within the group of certified centers.