Regional variation in all-cause mortality among breast cancer patients in Germany: an analysis using the PopGrouper

Background Breast cancer is the most common cancer among women in Germany. Although improvements in early detection and treatment have improved survival, differences in patient morbidity and healthcare delivery may contribute to regional variation in outcomes. All-cause mortality provides a measure that captures deaths related to both breast cancer and comorbid conditions. This study examines regional variation in all-cause mortality among breast cancer patients in Germany, using the PopGrouper as a novel morbidity adjustment tool. Methods Claims data from the BARMER sickness fund for 2022–2023 were analyzed for actively treated breast cancer patients ( n = 28,446). First, PopGroup-standardized observed-to-expected (O/E) ratios were calculated to describe regional variation of all-cause mortality in 2023, compared to the national average. Subsequently, the PopGrouper was used in multilevel regression analyses to analyze the association between age, morbidity, and all-cause mortality. Results After PopGroup-standardization, O/E mortality ratios ranged between 0.4 and 2.0 between regions (coefficient of variation = 20%). The regression analysis did not confirm statistically significant differences in mortality between regions, but between age and morbidity groups. Conclusion The PopGrouper can be used both for indirect standardization as in the O/E analyses and in regression models. Comparing both approaches can provide complementary perspectives and a more comprehensive assessment of regional variation. The PopGrouper represents a valuable tool for adjusting for morbidity-related care needs in regional comparative analyses.