The aim of this study is to learn more about how physical activity and cardiorespiratory fitness are related to diabetes risk among breast cancer patients prescribed an endocrine therapy.

80 women between the ages of 18-80 years will be recruited for this study. The study design consists of two separate in-person visits to University of Colorado Anschutz Medical Campus or Colorado State University. The study consists of glucose testing, a body composition scan, exercise testing, and a two-week period of free living activity monitoring.

Inclusion Criteria:

• Female
• diagnosed with breast cancer
• age 18-80 years
• Completed surgery, chemo- and/or radiation therapy
• Prescribed aromatase inhibitor or SERM for at least one year from the time of screening

Exclusion Criteria:

• Age < 18 or > 80

• Type 1 diabetes

• Type 2 diabetes

• Prescribed anti-hyperglycemic medication, insulin, or sulfonylurea.

• Pregnant, breastfeeding or planning to become pregnant in next 2 months

• Have absolute contraindications to exercise testing which are:

  1. Unstable angina
  2. Recent myocardial infarction, cardiac surgery, or vascular surgery (<3 months)
  3. Uncontrolled high blood pressure
  4. Heart failure
  5. Peripheral artery disease (based on report of symptomatic claudication)
  6. Hepatic or renal disease
  7. Severe arthritis or mobility impairment that would interfere with exercise testing

• Suspected cognitive impairment that would prevent understanding or comprehension of study procedures.

Biologically female.

Breast cancer survivors prescribed endocrine therapy for at least one year