Letrozole and Imatinib Mesylate in Treating Postmenopausal Participants With Estrogen or Progesterone Positive Metastatic Breast Cancer

PRIMARY OBJECTIVES: I. To determine the efficacy of letrozole plus imatinib mesylate in patients with estrogen receptor (ER) and or progesterone receptor (PgR) positive metastatic breast cancer. II. To determine the safety and tolerability of letrozole plus imatinib mesylate in patients with metastatic breast cancer. III. To determine the time to disease progression and overall survival in patients with metastatic breast cancer who are treated with letrozole plus imatinib mesylate. OUTLINE: Participants receive imatinib mesylate orally (PO) twice daily (BID) and letrozole PO once daily (QD) for 8 weeks in the absence of disease progression or unacceptable toxicity. After completion of study treatment, participants are followed up at 1 and 4 weeks and at 2, 4, 6, 9, and 12 months.