Dose-Response of Aerobic Training in Women at High-Risk for Development of Breast Cancer

Inclusion Criteria: * Women at high-risk of breast cancer as defined by one of the following: * Cytologically confirmed atypical hyperplasia * Cytologically confirmed LCIS * Being a carrier for * BRCA1 and/or BRCA2 * Predicted lifetime risk of breast cancer \>20% based on family history) * Predicted 10-year risk of breast cancer of ≥ 2.31% * Predicted 5-year risk of breast cancer ≥ 1.67% * Aged 21 ≤ 80 years old * If a female of child-bearing potential, must not be pregnant or planning to become pregnant during the study. * Women \<50 years old who are of child-bearing potential must have a negative pregnancy test (urine HCG or serum) within 14 days of enrollment. * Must a negative mammogram or negative breast MRI within 1 year of protocol required baseline core biopsy * Clinical breast exam interpreted as benign (not suspicious for cancer) at MSK * Performing less than or equal to 120 minutes of structured moderate-intensity or strenuous-intensity exercise per week * Able to complete an acceptable baseline CPET in the absence of high risk ECG findings or other inappropriate response to exercise as determined by the investigator. * Able to achieve an acceptable peek baseline CPET defined as by any of the following criteria: * achieving a plateau in oxygen consumption concurrent an with increase in power output; * a respiratory exchange ratio ≥ 1.10; * attainment of maximal predicted heart rate (HRmax) (i.e., within 10 bpm of age-predicted \[HRmax = 220-Age\[years\]) Volitional exhaustion, as measured by a rating of perceived exertion (RPE) ≥ 18 on the BORG scale. Exclusion Criteria: * Use of any selective estrogen receptor modulator or aromatase inhibitor within 6 months of randomization, including, but not limited to: (tamoxifen, raloxifene, arzoxifene, acolbifene, anastrozole, exemestane, and letrozole) * Enrollment on an interventional investigational study * Bilateral breast implants * Any newly identified breast abnormality requiring surgical excision * History of any of the following: * Invasive cancer diagnosis * DCIS * Any current invasive cancer diagnosis * Metastatic malignancy of any kind * Any other condition or intercurrent illness that in the opinion of the investigator makes the subject a poor candidate for core biopsy or the trial * Mental impairment leading to inability to cooperate. * Room air desaturation at rest ≤85% * Any of the following absolute contraindications to cardiopulmonary exercise testing and/or aerobic training: * Acute myocardial Infarction (within 3-5 days of any planned study procedures); * Unstable angina; * Uncontrolled arrhythmia causing symptoms or hemodynamic compromise; * Recurrent syncope; * Active endocarditis; * Acute myocarditis or pericarditis; * Symptomatic severe aortic stenosis; * Uncontrolled heart failure; * Acute pulmonary embolus or pulmonary infarction within 3 months of any planned study procedures; * Thrombosis of lower extremities; * Suspected dissecting aneurysm; * Uncontrolled asthma; * Pulmonary edema; * Respiratory failure; * Acute non-cardiopulmonary disorders that may affect exercise performance or be aggravated by exercise (i.e. infection, renal failure, thyrotoxicosis); or