This study is being done to see if the investigators can measure changes that occur in breast tissue when women at risk of developing breast cancer start an exercise program. The investigators are interested in studying this because research shows that women who exercise regularly are less likely to develop breast cancer, but there is not very much information explaining how exercise could affect breast cells in a way to prevent cancer from occurring. In this research study the investigators will use a research technique called breast random fine needle aspiration (RPFNA) to test breast cells for their shape and how they look. The investigators will look at breast cells before and after a participant takes part in an exercise program to see if the investigators are able to see any changes in breast cells that could have happened due to the exercise program. This research will help us to develop larger projects to see if exercise programs could be helpful in preventing breast cancer.

Inclusion Criteria:

• History of lobular carcinoma in situ, atypical ductal/lobular hyperplasia on prior breast biopsy or lifetime risk of breast cancer of at least 20% based on any risk model, or personal history of BRCA1 or 2 mutation
• Physically able to exercise and physician consent to start an exercise program
• Sedentary activity pattern
• Premenopausal
• English speaking and able to read English

Exclusion Criteria:

• History of invasive breast cancer or ductal carcinoma in situ
• Absolute contraindications to maximal exercise testing as recommended by the American Thoracic Society
• Any condition which in the investigator's opinion makes the subject unsuitable for study participation
• Participating in another clinical study with competing study outcomes
• Pregnant or breastfeeding
• Unable to comply with protocol and/or not available for follow-ups
• Type II Diabetes
• Allergic to local anesthetics
• History of bilateral or unilateral mastectomy