Factors Associated with Prolonged Hospitalisation in Women with Breast Cancer: Evidence from a Large German Multicentre Study

Background/Objectives: Breast cancer is the most common malignancy among women worldwide and poses a significant burden on healthcare systems. Despite evidence that treatment type is associated with hospital length of stay (LOS), current Germany-wide data on this topic are lacking. The present study aims to identify clinical and procedural factors associated with prolonged hospitalisation in women hospitalised for breast cancer in Germany. Methods: This multicentre cross-sectional study analysed anonymised inpatient data from 38 German hospitals (IQVIA database), including 16,062 female breast cancer hospitalisation episodes (inpatient cases; patient-level linkage was not possible due to anonymisation, so these may not represent 16,062 distinct women) treated between January 2019 and December 2024. The primary outcome was LOS; prolonged hospitalisation was defined as LOS > 7 days (75th percentile). Comorbidities were assessed using individual comorbidity categories defined according to the Elixhauser classification (retained at ≥1% prevalence). The primary multivariable analysis was restricted to characteristics documented independently of the in-hospital course (age, tumour site, metastatic status, chronic comorbidities). In-hospital complications, procedures, and diagnoses of ambiguous timing were analysed separately as secondary, descriptive associations. LOS was modelled using negative binomial regression (Poisson regression as a sensitivity analysis) and prolonged LOS using logistic regression, both with hospital-clustered robust (sandwich) standard errors. Results: The overall median LOS was 4 days (IQR 3–7); 19.3% of hospitalisation episodes were prolonged. In the primary analysis, longer LOS was associated with age > 70 years (RR 1.14; 95% CI 1.08–1.20), distant metastases (RR 1.76; 95% CI 1.51–2.04), lymph node metastases (RR 1.09; 95% CI 1.05–1.12), congestive heart failure (RR 1.44; 95% CI 1.31–1.59), anaemia (RR 1.41; 95% CI 1.14–1.75) and depression (RR 1.14; 95% CI 1.03–1.26). In the secondary descriptive analysis, in-hospital complications showed the strongest associations with longer LOS, particularly postoperative infection (RR 2.28), wound disruption (RR 1.92) and pneumonia (RR 1.45). Breast-conserving surgery and partial breast resection were associated with shorter LOS, while mastectomy, blood transfusions, and complex intensive care were associated with prolonged stays; the small inpatient radiotherapy subgroup (1.9%) most likely reflects a highly selected, predominantly palliative population rather than an association attributable to radiotherapy itself. Conclusions: Prolonged hospitalisation was associated with older age, documented lymph node and distant metastases, and chronic somatic comorbidities including congestive heart failure, anaemia, chronic kidney disease and depression, and, in secondary descriptive analyses, with perioperative complications and intensive procedures. The strongest correlates of prolonged stay—in-hospital complications and intensive procedures—are documented during rather than before the hospitalisation and therefore cannot themselves support early risk identification; however, the baseline characteristics documented independently of the in-hospital course (age, metastatic disease, chronic comorbidity burden) may usefully inform structured perioperative management and discharge planning in Germany.