The investigators are doing this study to determine if there are body composition changes after a 12-week exercise program in breast cancer patients and determine what factors contribute to sustained physical activity after the 12-week exercise program intervention.

The study is enrolling breast cancer patients up to 2 years after their diagnosis in a 12-week exercise program. The participants will either participate in: Group 1-participating in an exercise program with biometric evaluations or Group 2-biometric evaluations but not participating in the exercise program. At the end of the 12-week exercise program, participants in Group 1 will be randomized to either: a) continuing with exercise group classes or b) continuing with exercise individual classes. Both Group 1a and 1b participants will be followed for the remainder of the year and be evaluated for continued physical activity. All Group study participants' biometrics will be assessed at baseline and at the end of 12-weeks, with continued annual medical review follow-up for a total of 5 years.