Impact of hospital volume on breast cancer outcome: a population-based study in the Netherlands

For low-volume tumours, high surgical hospital volume is associated with better survival. For high-volume tumours like breast cancer, this association is unclear. The aim of this study is to determine to what extent the yearly surgical hospital breast cancer volume is associated with overall survival. All patients, diagnosed with primary invasive non-metastatic breast cancer in the period 2001-2005, were selected from the Netherlands Cancer Registry. Hospitals were grouped by their annual volume of surgery for invasive breast cancer. Cox proportional hazard models were used including patient and tumour characteristics as covariates. Follow-up was completed until the 1st of February 2013. Primary endpoint was 10-year overall survival rate. In total, 58,982 patients with invasive non-metastatic breast cancer were diagnosed during the period 2001-2005. Hospitals were grouped by their (mean) annual surgical volume: <75 (n = 19), 75-99 (n = 30), 100-149 (n = 29), 150-199 (n = 9) and ≥200 (n = 14). The 10-year observed survival rates were 77, 81, 80, 82 and 82 %, respectively. After case-mix adjustment, patients in low-volume hospitals had a HR of 1.09 (<75 vs. ≥200; 95 % CI 1.03-1.15). Survival was significantly higher for lobular carcinoma and for diagnosis in the most recent year (2005). Being a male, having a higher age at diagnosis, a higher tumour grade, a larger tumour size, a higher number of positive lymph nodes, an earlier year of diagnosis and a lower SES resulted in a reduced survival and influenced death, all to a larger extent than surgical volume did. In the Netherlands, surgical hospital volume influences 10-year overall survival only marginally and far less than patient and tumour characteristics. No difference in survival was revealed for invasive non-metastatic breast cancer patients in hospitals with 75-99 operations per year compared with hospitals with over 200 operations per year.