LAUSR

BACKGROUND Young premenopausal women with breast cancer often experience more aggressive disease biology and poorer survival than older women. Diagnostic and therapeutic advances, including human epidermal growth factor receptor 2 (HER2)-directed therapy, may lessen treatment burden and improve survival for these young women, but contemporary incidence and survival data by HER2 status are limited. PATIENTS AND METHODS We identified women aged 20-49 years (n = 68,530) diagnosed with stage I-III breast cancer during 2010-2016 from the United States Surveillance, Epidemiology, and End Results 18 registries database. Age-adjusted average annual percent changes in incidence (diagnosis 2010-2016) and 5-year Kaplan-Meier survival curves (diagnosis 2010-2015) were estimated by HER2 and hormone receptor (HR) status and stratified independently by cancer stage and race/ethnicity. RESULTS With increasing age decade, proportions of HER2-/HR+ cancer increased, whereas proportions of HER2+/HR+, HER2+/HR-, and HER2-/HR- decreased. The greatest increases in incidence during 2010-2016 were observed for HER2+ among women aged 20-49 years and HER2-/HR- among women aged 20-29 years. Incidence decreased for HER2-/HR- among women aged 40-49 years. Five-year survival was lowest for HER2-/HR- status compared to other receptor-based subtypes among women aged 20-49 years. HER2+ status was more beneficial for 5-year survival than HR+ status among women aged 20-29 years, with the opposite observed among women aged 30-49 years, particularly those aged 40-49 years. CONCLUSION HER2+ breast cancer increased among premenopausal women and was also associated with higher early survival within each HR status. HER2-/HR- cancer also increased among women aged 20-29 years and was associated with lower early survival. Our contemporary data provide important insights to help inform preventive and therapeutic strategies for premenopausal women.