This phase II trial studies how well exemestane before surgery works in treating postmenopausal patients with newly diagnosed estrogen receptor positive stage II-III breast cancer. Estrogen can cause the growth of breast cancer cells. Hormone therapy using exemestane may fight breast cancer by blocking the use of estrogen by the tumor cells.

This study will develop preliminary data regarding the efficacy and safety of exemestane in the preoperative treatment of postmenopausal women with ER+ or PR+ tumors. This trial is also designed to develop a predictive model to correlate expression of the known isoforms of ER and progesterone receptor (PR) and the aromatase enzyme with response to estrogenic deprivation using exemestane.

Inclusion Criteria:

• Histologically or cytologically confirmed breast cancer
• ER positive (+)
• Primary tumor 2-4 regional lymph nodes 0-2 (T2-4N0-2); patients may have metastatic disease, provided local-regional surgery is clinically indicated
• Clinical stage II/III
• Postmenopausal- defined as having had a previous bilateral oophorectomy or, for women with no prior hysterectomy, the absence of spontaneous menstrual cycles for more than 1 year
• Newly diagnosed
• Patients with prior non-breast malignancies are eligible if they have been disease free for >= 5 years before study entry; patients with squamous or basal cell carcinoma of the skin that has been effectively treated, carcinoma in situ of the cervix that has been treated by surgery only, or lobular carcinoma in situ (LCIS) of the ipsilateral or contralateral breast that has been treated by surgery only are eligible, even if the cancer was diagnosed within 5 years before randomization
• Serum creatinine =< 1.5 x institutional upper limit of normal (ULN)
• Hemoglobin within normal limits for institution
• Absolute granulocyte count >= 1500
• Platelet count >= 100,000
• Serum glutamic oxaloacetic transaminase (SGOT), aspartate aminotransferase (AST) or serum glutamate pyruvate transaminase (SGPT), alanine aminotransferase (ALT) =< 2.5 x ULN
• Total bilirubin < 2 x ULN for institution
• Alkaline phosphatase < 2 x the ULN

Exclusion Criteria:

• Completely resected
• Prior hormone or chemotherapy
• Unable to take oral medication
• Patients who have nonmalignant systemic disease (cardiovascular, renal, hepatic, etc.) that would preclude their being subjected to protocol therapy

Consent to surgery (approximately four months)

Adverse event collection and reporting not required by protocol. Only SAE reporting required.