Prognostic Factors of Survival among Women with Metastatic Breast Cancer and Impact of Primary or Secondary Nature of Disease on Survival: A French Population-Based Study

We aim to determine whether differences in survival exist between two populations of women with metastatic breast cancer (MBC) and to identify prognostic factors of survival after metastasis diagnosis. Data on women with MBC diagnosed between 2000 and 2011 were provided by the Cote d'Or Breast cancer registry. Survival rates and median overall survival (OS) after metastasis diagnosis were determined using the Kaplan-Meier method and prognostic factors were determined in a Cox proportional hazard model. Overall, 282 women with primary MBC and 340 with secondary MBC were included. A 2-year survival rate was significantly better in women with primary MBC (50.8% [95% CI: 47.8-53.8%] versus 44.5% [95% CI: 41.8-47.2%]). However, median OS did not differ between the two groups (p = 0.1). The prognostic factors associated with worst survival were a triple-negative tumor type (p < 10(-4)), multiple metastases sites (p < 10(-4)), an older age at metastasis (p < 10(-4)), and a SBR grade G3 (p = 0.007). OS between women with primary MBC and women with secondary MBC does not seem to differ significantly. This population-based study provides original epidemiological data on French women without any selection bias inherent to hospital cohorts.