The study will also evaluate multiple factors that may help doctors predict who will tolerate the therapy without having their ovaries start making estrogen again. Some of the factors to be evaluated include other hormone levels (blood tests) as well as family history of early menopause (mother, sisters). In addition, changes in certain genes that affect how patients' bodies handle chemotherapy drugs will be tested to see if they affect whether or not patients recover ovarian function. Overall, the purpose of the study is to determine which patients who become postmenopausal from chemotherapy are likely to tolerate aromatase inhibitor treatment safely, and how often the patients' ovarian function needs to be tested during treatment.