Feasibility of Quality Indicators to assess the Prevalence of Guideline Adherence in a German Cohort of Patients with Advanced or Metastatic Breast Cancer: Results of the BRE-BY-MED study

• 12 QIs were used to define guideline adherence in patients with metastatic breast cancer (mBC). • The use of QIs was partially feasible to estimate the prevalence of guideline adherence in mBC. • The median guideline adherence was 66.7%. • The highest adherence was observed for biopsy, endocrine therapy and radiotherapy. In Germany, the national evidence- and consensus-based S3-Guideline guide treating physicians on effective therapies. Data on guideline adherence in patients with advanced or mBC in everyday clinical practice are lacking for Germany. The aim of the present study was to test the feasibility of quality indicators (QIs) to assess guideline adherence in a German cohort of patients with advanced or mBC. Between July 2022 and February 2024, adults with advanced or mBC, living in Bavaria, were included in the BRE-BY-MED “Breast Cancer Care in Bavaria for Patients with Metastatic Disease” cohort study (DRKS00026601) at the University Hospital Würzburg. 12 QIs based on the S3 guideline were used to define guideline adherence of first-line therapies in routine medical records. Guideline adherence was defined by a cut-off of 75%, based on clinical expertise. 93 patients (median age 57 years; IQR=48-64), were consecutively enrolled in the BRE-BY-MED study. The median guideline adherence was 66.7% (IQR=50.0-100.0%). The highest guideline adherence was observed for biopsy of distant metastasis (77.4%), endocrine therapy in first-line in HR+ (66.0%), no chemo-endocrine therapy in first-line in HR+ (98.1%), and radiotherapy for nodal-positive BC (72.7%). Four QIs could not be analysed based on the available data. The use of QIs was partially feasible to estimate the prevalence of guideline adherence in advanced or mBC patients. Therapies and therapy recommendations in the field of advanced or mBC therapy can evolve very rapidly over time. Furthermore, treatment recommendations are often individualised for these patients. This may not be reflected in guidelines or QIs.