This pilot study tests the effects of aerobic exercise training on cognitive function in breast cancer survivors (BCS). Participants will be randomized to a 12-week walking intervention or usual care. Walking participants will attend small group sessions led by an exercise specialist 3 times weekly. Usual care participants will complete baseline and post-testing and be offered two sessions with an exercise specialist. All participants will complete a fitness test, electrophysiology, and patient-reported outcomes at baseline and post-intervention. A subset of participants will also be invited to undergo magnetic resonance imaging (MRI). The investigators will generate preliminary data on clinical and biological correlates of exercise and cognition, including treatment protocol, cardiorespiratory fitness, brain structure and function, and cancer-related fatigue.

Aim 1: This pilot study tests the effects of aerobic exercise training on cognitive function in breast cancer survivors (BCS). To test aim 1, the investigators will randomize up to forty post-menopausal BCS (3-24 months post-treatment) to a 12-week walking intervention (n=20) or usual care (n=20). Walking participants will attend small group (n=3-5 BCS) sessions led by an exercise specialist 3 times weekly. Usual care participants will complete baseline and post-testing and be offered two sessions with an exercise specialist after all data have been collected. Aim 1 measures include accelerometry, neurocognitive testing, and patient-reported outcomes at baseline and post-intervention.

Aim 2: The investigators will generate preliminary data on clinical and biological correlates of exercise and cognition, including treatment protocol, cardiorespiratory fitness, brain structure and function, and cancer-related fatigue. To test aim 2, all participants will complete a fitness test, electrophysiology, and patient-reported outcomes at baseline and post-intervention. A subset of participants will also be invited to undergo magnetic resonance imaging (MRI).

Data will be analyzed using descriptive statistics and analysis of covariance, and effect sizes expressed as standard mean difference will be calculated.

Inclusion Criteria:

• Female
• Post-menopausal at time of diagnosis
• First, primary diagnosis of Stage I-IIIa breast cancer
• Completed treatment 3-24 months prior to study start
• Available to attend exercise sessions 3 times weekly for 12 weeks
• No scheduled travel >7 consecutive days during the intervention
• Agree to be randomized
• Willingness to wear, charge, and sync Fitbit
• English reading and speaking
• Physician's clearance to exercise
• Provide written informed consent

Exclusion Criteria:

• Males
• Pre- or peri-menopausal at the time of diagnosis
• Stage 0 or metastatic disease
• Currently receiving chemotherapy or radiation therapy
• More than 24 months post-treatment
• Scheduled to receive breast surgery
• Second cancer diagnosis (excluding non-invasive skin cancers)
• Self-report an average of ≥60 minutes of moderate to vigorous physical activities (MVPA) per week for the previous 6 months
• Not cleared to exercise by a physician
• Not available to attend 3 times weekly exercise sessions for 12 weeks
• Out of town travel scheduled for >1 week during the intervention
• Unwilling to complete baseline assessments
• Unwilling to be randomized to the exercise or control group
• Unwilling to wear, charge, and sync the Fitbit during the study period
• Unable to read and speak in English
• Unwilling to provide written informed consent to participate
• Cognitive impairment prior to baseline assessment
• History of stroke, transient ischemic attack, other neurological disorders, or brain surgery involving tissue removal

De-identified data will be available upon request as required by journal publishers during dissemination phase of the study.

When summary data are published.

Individual participant data (IPD) will be provided as required by journals in which summary data are published.