Varying Prognostic Impact Of Molecular Subtype Among Young Patients With De Novo Stage Iv Breast Cancer: A Population-Based Cohort Study.

e13090Background: Younger patients with early stage breast cancer have been reported to have worse prognosis compared to older patients while reverse relationship has been demonstrated in stage IV breast cancer. We aimed to determine clinicopathologic features of young patients with stage IV breast cancer and the overall survival (OS) difference stratified by molecular subtypes. Methods: We performed a retrospective cohort study using the Surveillance, Epidemiology, and End Results database from 2010 to 2014. We included patients (age 19-59 years) diagnosed with stage IV breast cancer. The patients were divided into two groups, young age ( u003c 40 years) and middle-aged (40-59 years). Molecular subtypes were classified as: hormone receptor (HR)+/human epidermal growth factor receptor 2 (HER2)-, HR+/HER2+, HR-/HER2+ and HR-/HER2-. We used log-rank test and Cox proportional hazards model adjusting for potential confounders to examine the OS between groups and repeated the analysis with stratification by molecu...