3. Patients with histologically proven ductal carcinoma in situ (DCIS/stage 0) or stage I-III invasive carcinoma of the breast that is ER and/or PR positive by immunohistochemical staining, who are considering aromatase inhibitor therapy. Patients must have completed any adjuvant chemotherapy. Patients may have received preoperative chemotherapy. Patients should have also completed local therapy; however, enrollment/initiation of aromatase inhibitor on study may be done prior to completion of radiation therapy. Women may receive the aromatase inhibitor on this study as initial adjuvant hormonal treatment or following adjuvant tamoxifen.