High-impact complications after breast cancer surgery in the Dutch national quality registry: evaluating case-mix adjustment for hospital comparisons
Authors: Verheul Elfi M , van Klaveren David , Lingsma Hester F , Vos Elvira , Hoornweg Marije J , Siesling Sabine , Koppert Linetta B ,   NBCA consortium, Hellingman Alwine A , Moorman A M , Francken Anne Brecht , van der Vegt Bert , Meeuwis Carla , de Betue Carlijn T I , van Deurzen Carolien H M , Loo Claudette E , Contant Caroline M E , Paez Cristina Guerrero , den Hoed D M , Henneman Daniel , van Uden Dominique J P , Frakking Tanja G , Van Dessel Els , Bantema-Joppe Enja J , Schoenmaeckers Ernst J P , Siemerink Ester , Verbeek Floris P R , Gooiker Gea A , Schuttevaer Henriette , Rakhorst Hinne A , Kappers Ingrid , van den Hoven Ingrid , Van Bastelaar James , Verloop Janneke , Volders José H , Heijns Joan B , Meijer Joyce , Beelen Karin J , van Engelen Klaartje , Dols Leonienke F C , de Munck Linda , van Hezewijk Marjan , Bosscher M R F , Menke-Pluijmers Marian B E , Schlooz-Vries Margrethe , Straver Marieke E , Beek Martinus A , Bessems Maud , Gordinou de Gouberville Marije C , Martens Milou H , Hoven-Gondrie Miriam L , Vrancken Peeters Marie-Jeanne T F D , Jansen Patricia , Neijenhuis Peter A , Bijlsma Rhodé M , Schipper Robert-Jan , van Eekeren Ramon R J P , Schok Thomas , van Sprundel Tim C , Damen Tim H C , Lans Titia E , Tjan-Heijnen Vivianne C G , Vissers Yvonne L J 
Published: February 2025

Abstract

Background
Comparison of quality indicators can improve quality of care. However, case-mix adjustment is deemed essential. The aim of this study was to develop and validate case-mix adjustment models and to evaluate the effect of case-mix adjustment for the quality indicators related to complications after breast cancer surgery.

Methods
Multivariable logistic regression with backward selection (P &lt; 0.1) was used to develop case-mix models in patients undergoing breast cancer surgery (all types, breast-conserving surgery, mastectomy with or without immediate reconstruction) in the Netherlands (NABON Breast Cancer Audit). High-impact complications were defined as Clavien Dindo grade ≥3. Model performance was assessed using the area under the receiver operating characteristic curve (AUC), corrected for optimism with bootstrap validation. Observed-to-expected plots were used to visualize the difference between unadjusted and case-mix adjusted hospital performance (hospital shifts).

Results
In total 32 084 patients from 72 hospitals treated in 2021–2022 were included. A between-hospital variation in complication rates was observed for all surgeries (interquartile range 2.4–6.0%), breast-conserving surgery (interquartile range 1.4–3.4%), and mastectomy with (interquartile range 9.4–9.1%) and without reconstruction (interquartile range 3.3–9.7%). Of the considered variables, body mass index, smoking, multifocality and neoadjuvant therapy were weakly associated with complications. However, surgery type was strongly related to complications (AUC 0.70), resulting in noticeable hospital shifts in the quality indicator scores comprising all surgeries. After stratification for surgery type, no evident hospital shifts were observed after case-mix correction.

Conclusion
For valid comparison of complication rates after breast cancer surgery between hospitals, stratification by surgery type is crucial. Subsequently, the evaluated patient and tumour characteristics have a negligible effect on the hospital variation.