Introduction: Young women have poorer survival after breast cancer than do older women. It is unclear whether
this survival difference relates to the unique distribution of hormone receptor (HR) and human epidermal growth
factor receptor 2 (HER2)-defined molecular breast cancer subtypes among adolescent and young adult (AYA)
women aged 15 to 39 years. The purpose of our study was to examine associations between breast cancer
subtypes and short-term survival in AYA women, as well as to determine whether the distinct molecular subtype
distribution among AYA women explains the unfavorable overall breast cancer survival statistics reported for AYA
women compared with older women.