Endocrine therapy (ET) is widely used to treat hormone receptor positive breast cancer and prevent recurrence by downregulating estrogen function. However, ETs readily cross the blood brain barrier and interfere with the action of estrogen in the brain. Estrogen supports cognition and menopausal status is closely linked to cognitive health in women. This has raised concern that anti-estrogen ETs may affect cognition and brain health in breast cancer survivors. However, evidence across existing studies is inconsistent and these effects remain poorly understood. The incomplete understanding of the effects of ET are likely due to limitations of earlier studies - namely, the under-appreciation of the role of menopausal status and insensitivity of standard cognitive measures. This research project will address these earlier limitations by specifically comparing ET effects by menopausal status, and using highly sensitive, task-related functional magnetic resonance imaging (fMRI) measures to assess the effects of ET on brain function.