Patients with histologically-confirmed, HR-positive (ER and/or PR), HER2-negative metastatic breast cancer (MBC)

Postmenopausal status defined by lack of menses for 2 years, oophorectomy, or medical ovarian suppression

Receiving first line endocrine-based therapy (tamoxifen, aromatase inhibitor, or fulvestrant; concurrent molecular therapy also allowed)

Sedentary (i.e., \<60 minutes / week of exercise)

Age \>18 years

BMI ≥ 18.5

Cleared for exercise participation as per screening clearance via PAR-Q+

Cleared for study participation as per screening consultation with an MSK Exercise Physiologist

Willingness to comply with all study-related procedures

Patients with "treated and stable" brain lesions of a duration of ≥ 2 months may be enrolled

Exercise Treatment With Standard Therapy for Metastatic Breast Cancer