Exemestane in Treating Postmenopausal Women With Stage IV Breast Cancer

RATIONALE: Estrogen can cause the growth of breast cancer cells. Hormone therapy using exemestane may fight breast cancer by lowering the amount of estrogen the body makes. PURPOSE: This phase II trial is studying how well exemestane works in treating postmenopausal women with stage IV breast cancer.

PRIMARY OBJECTIVES: I. Progression-free survival at 4 months, as measured by Response Evaluation Criteria in Solid Tumors (RECIST). SECONDARY OBJECTIVES: I. Objective response rate (complete response \[CR\] and partial response \[PR\]). II. Clinical benefit (CR, PR, and stable disease \>= 6 months). III. Assessment of toxicity. IV. Assessment of compliance with medication adherence. V. Assessment of quality of life. VI. Assessment of bone health. TERTIARY OBJECTIVES: I. Serial measurements of serum estradiol, estrone, and estrone sulfate. II. To investigate treatment resistance (e.g., expression of amphiregulin, epidermal growth factor receptor \[EGFR\]), using molecular and immunohistochemical analyses of blood and tumor samples of pre- and post- (when available) treatment tissues. Microarray analyses to quantitate the expression of specific estrogen-responsive genes (e.g. thyroid transcription factor 1 \[TTF1\] and PDZK1) will also be performed. OUTLINE: Patients receive exemestane orally (PO) once daily (QD) on days 1-14. Courses repeat every 21 days in the absence of disease progression or unacceptable toxicity. After completion of study therapy, patients are followed periodically for 1 year.