Fasting & ExerciseProlonged Overnight Fasting and/or Exercise on Fatigue and Other Patient Reported Outcomes in Women With Hormone Receptor Positive Advanced Breast Cancer

Inclusion Criteria:

1. Women
2. Able to provide written informed consent
3. Able to speak, read, and understand English or Spanish
4. Postmenopausal (including concurrent use of ovarian suppression)
5. Diagnosis of ER+ and/or PR+, hormone estrogen receptor-2 (HER-2)- or HER-2+ metastatic or locally advanced unresectable breast cancer
6. Initiation of endocrine therapy in combination with a CDK4/6 inhibitor (e.g., palbociclib, ribociclib, or abemaciclib), with or without hormone estrogen receptor-2 (HER2)-directed therapy (e.g., trastuzumab ± pertuzumab), or in combination with both a CDK4/6 inhibitor and a Phosphoinositide 3-kinase (PI3K) or Protein kinase B (AKT) inhibitor, within the past 90 days.

a) Participants who switch from one CDK4/6 inhibitor to another due to toxicity or insurance constraints remain eligible, provided enrollment occurs within 90 days of initiating the subsequent CDK4/6 inhibitor in the metastatic or locally advanced setting.
7. Having not consistently (not equal to or more than 50% of the time) engaged in more than 90 minutes of moderate or 45 minutes of vigorous physical activity per week over the past 3 months
8. Having not consistently engaged in resistance training 2 or more days per week over the past 3 months
9. Having not consistently (not equal to or more than 50% of the time) engaged in structured fasting (i.e., not regularly fasting for ≥12hr/night) for the past 3 months
10. Approval from a medical oncology provider to participate.

Exclusion Criteria:

1. Unable to provide consent
2. Unable to read or understand English or Spanish
3. Dependent on supplemental oxygen
4. Unstable cardiac disease
5. Insulin-dependent diabetes
6. Unable to walk 2 blocks without assistance (excluding canes)
7. Regularly maintaining a shiftwork schedule, i.e. working evening shifts, night shifts, or rotating shifts in the last 3 months
8. History of a clinical eating disorder
9. Unstable bone metastases
10. More than 90 days since initiation of endocrine therapy in combination with 1) a CDK4/6 inhibitor, with or without HER2-directed therapy, or 2) a CDK 4/6 inhibitor in combination with a PI3K/AKT inhibitor, in the metastatic or locally advanced.
11. Presence of a severe medical condition or psychiatric condition or medications that would preclude participation of the study intervention.