The investigators hypothesize that exercise in postmenopausal breast cancer survivors will result in an increase in the plasma concentrations of angiostatic factors and a decrease in the plasma concentrations of angiogenic factors. Exercise is expected to result in a circulating angiostatic phenotype that inhibits adipose tissue mass, growth of breast cancer tumor, growth of microscopic residual disease after breast cancer resection, decreases rates of local-regional recurrence, decreases rates of distant recurrence, and increases survival.