Colorectal Cancer Survival in German–Danish Border Regions—A Registry-Based Cohort Study

SIMPLE SUMMARY: This study reports updates on colon and rectum cancer survival differences in the German–Danish border region and investigates the effects of tumor stage at diagnosis and first-line treatment on cancer survival. Based on cancer registry data from 2004 to 2016, we estimated the risk of dying from all causes after a colon or rectum cancer diagnosis while also controlling for stage and treatment. We observed that colon and rectum cancer survival improved in the entire German–Danish border region, but much more in the Danish regions. At first, colon and rectal cancer survival was higher on the German side of the border, but the Danish regions caught up. In the end, colon cancer survival was similar across the border and rectal cancer survival was better in Denmark. Stage and treatment could not explain the observed survival differences. Health care reforms and early detection strategies may also contribute to the regional differences. ABSTRACT: The aim of this study was (i) to update the reporting of colorectal cancer survival differences over time in the German–Danish border region (Schleswig-Holstein, Southern Denmark, and Zealand) and (ii) to assess the extent to which it can be explained by stage and primary treatment. Incident invasive colorectal cancer cases diagnosed from 2004 to 2016 with a follow-up of vital status through 31 December 2017 were extracted from cancer registries. Analyses were conducted by anatomical subsite and for four consecutive periods. Kaplan–Meier curves and log-rank tests were computed. Cox regression models using data from Schleswig-Holstein from 2004 to 2007 as the reference category were run while controlling for age, sex, stage, and treatment. The cox regression models showed decreasing hazard ratios of death for all three regions over time for both anatomical subsites. The improvement was stronger in the Danish regions, and adjustment for age, sex, stage, and treatment attenuated the results only slightly. In 2014–2016, colon cancer survival was similar across regions, while rectal cancer survival was significantly superior in the Danish regions. Regional survival differences can only partially be explained by differing stage distribution and treatment and may be linked additionally to healthcare system reforms and screening efforts.