Counterfactual approach with survival or time to event outcomes: An application to an exhaustive cohort of Epithelial Ovarian Carcinoma in the Rhône-Alps region of France.

Summary Epithelial Ovarian Carcinoma (EOC) is a disease with poor prognosis, most often diagnosed at an advanced stage, thus necessitating aggres sive and complex surgery. The aim of this study was to compare Progression Free Survival (PFS) at 1st line treatment of EOC patients treated in high vs low-volume hospitals. This retrospective study using prospectively implemented databases was conducted o n an exhaustive cohort of 267 patients treated in first line during 2012 in the Rhone-Alps Region of France. In order to control for selection bias, a multivariate analysis and the Inverse Probability Weighting (IPW) using the propensity score were adopted. An Adjusted Kaplan Meier Estimator (AKME) and a univariate Cox model in the weighted sample were then applied in order to determine the impact of the centralization of care on EOC. Patients treated in lower volume hospitals had a probability of relapse (including death) that was 1.5 times higher than for patients treated in higher volume hospitals (p=0.02). As reported in other countries, the concentration of care for EOC has a significant positive impact on patient outcomes .