Investigating the correlation between hospital of primary treatment and the survival of women with breast cancer

BACKGROUND. To understand the relation between hospital of initial treatment andthe survival of women with breast cancer, the authors investigated the characteristics of the treatment center that were related most to outcome. METHODS. The authors selected women from 5 regions of Quebec, Canada, who were diagnosed with lymph node-negative breast cancer between 1988 and 1994. Data were collected by chart review, queries to physicians, and linkage with administrative data bases. Overall survival to the end of 1999 was analyzed using the Kaplan-Meier method and Cox proportional hazards models. RESULTS. The study population included 1727 women with a median follow-up of 6.8 years. The 7-year survival rate was 82% (95% confidence interval [95%CI], 80-84%). Compared with women who were treated in centers with 100 new cases per year, the hazard ratio (HR) of death from any cause was 1.80 (95%CI, 1.23-2.63), 1.44 (95%CI, 1.03-2.03), and 1.30 (95%CI, 0.96-1.76) among women who were treated in hospitals with < 25 new cases, 25-49 new cases, and 50-99 new cases per year after adjusting for case mix and characteristics of the attending physician. However, the significance of caseload disappeared after adjusting for the type of hospital. By contrast, women who were treated in centers with either on-site radiotherapy, research activity, or teaching status had significantly better outcomes, even after adjusting for caseload (HR, 0.68; 95%CI, 0.50-0.92). These associations were independent of primary treatment received, which was a strong determinant of outcome. CONCLUSIONS. Primary treatment of early-stage breast cancer in larger hospitals was associated with improved survival. This relation was mediated by factors related to proficiency of care, which tended to cluster within institutions.