Breast cancer survival by teaching status of the initial treating hospital

Background: A number of studies have documented variation in treatment patt erns by treatment setting or by region. In order to better understand how t reatment setting. might affect survival, we compared the survival outcomes of women with node-negative breast cancer who were initially treated at tea ching hospitals with those of women initially treated at community hospital s. Methods: We constructed a retrospective cohort consisting of a random sampl e of 938 cases, initially diagnosed in 1991,drawn from the Ontario Cancer R egistry. Exposure was defined by the type of hospital in which the initial breast cancer surgery was performed. Outcomes were ascertained through foll ow-up of vital statistics. Results: The crude 5-year survival rate was 88.7% for women who had their i nitial surgery in a community hospital and 92.5% for women who had their in itial surgery in a teaching hospital. Women in higher income neighbourhoods experienced better survival at 5 years regardless of which type of hospita l they were treated in. Multivariate proportional hazards regression modell ing demonstrated a 53% relative reduction in risk of death among women with tumours less than or equal to 20 mm in diameter who were treated at a teac hing hospital (relative risk [RR] = 0.47, 95% confidence interval [CI] 0.23 -0.96), whereas among those with larger tumours there was no demonstrated d ifference in survival (RR = 1.32, 95% CI 0.73-2.32). Other variables that w ere significant in the model were age at diagnosis, estrogen receptor statu s and the use of radiation therapy. Interpretation: Women with node-negative breast cancer and tumours less tha n or equal to 20 mm in diameter who were initially seen at a teaching hospi tal had significantly better survival than women with similar tumours who w ere initially seen at a community hospital. Survival among women with large r tumours was not statistically significantly different for the 2 types of hospital.