Comparing quality of breast cancer care in the Netherlands and Norway by federated propensity score analytics

Purpose: The aim of the study was to benchmark and compare breast cancer care quality indicators (QIs) between Norway and the Netherlands using federated analytics preventing transfer of patient-level data. Methods: Breast cancer patients (2017–2018) were retrieved from the Netherlands Cancer Registry and the Cancer Registry of Norway. Five European Society of Breast Cancer Specialists (EUSOMA) QIs were assessed: two on magnetic resonance imaging (MRI), two on surgical approaches, and one on postoperative radiotherapy. The QI outcomes were calculated using ‘Vantage 6’ federated Propensity Score Stratification (PSS). Likelihood of receiving a treatment was expressed in odds ratios (OR). Results: In total, 39,163 patients were included (32,786 from the Netherlands and 6377 from Norway). PSS scores were comparable to the crude outcomes of the QIs. The Netherlands scored higher on the QI ‘proportions of patients preoperatively examined with breast MRI’ [37% vs.17.5%; OR 2.8 (95% CI 2.7–2.9)], the ‘proportions of patients receiving primary systemic therapy examined with breast MRI’ [83.3% vs. 70.8%; OR 2.3 (95% CI 1.3–3.3)], and ‘proportion of patients receiving a single breast operation’ [95.2% vs. 91.5%; OR 1.8 (95% CI 1.4–2.2)]. Country scores for ‘immediate breast reconstruction’ and ‘postoperative radiotherapy after breast-conserving surgery’ were comparable. The EUSOMA standard was achieved in both countries for 4/5 indicators. Conclusion: Both countries achieved high scores on the QIs. Differences were observed in the use of MRI and proportion of patients receiving single surgery. The federated approach supports future possibilities on benchmark QIs without transfer of privacy-sensitive data.