Letrozole in Preventing Cancer in Postmenopausal Women Who Have Received 4-6 Years of Hormone Therapy for Hormone Receptor-Positive, Lymph Node-Positive, Early-Stage Breast Cancer

Inclusion Criteria

• DISEASE CHARACTERISTICS: - Confirmed diagnosis of prior operable, noninflammatory breast cancer meeting the following criteria: - Steroid hormone receptor-positive tumors (estrogen receptor and/or progesterone receptor), determined by immunohistochemistry, after primary surgery and before commencement of prior endocrine therapy - Prior local treatment including surgery with or without radiotherapy for primary breast cancer with no known clinical residual loco-regional disease - Following primary surgery, eligible patients must have had evidence of lymph node involvement either in the axillary or internal mammary nodes, but not supraclavicular nodes - Clinically disease-free - Must have completed 4-6 years of prior adjuvant selective estrogen receptor modulators (SERMs), aromatase inhibitors (AIs), or a sequential combination of both - When calculating 4-6 years, neoadjuvant endocrine therapy should not be included - No evidence of recurrent disease or distant metastatic disease - No prior bilateral breast cancer PATIENT CHARACTERISTICS: - Female - Must be postmenopausal by any of the following criteria: - Patients of any age who have had a bilateral oophorectomy (including radiation castration AND amenorrheic for > 3 months) - Patients 56 years old or older with any evidence of ovarian function must have biochemical evidence of definite postmenopausal status (defined as estradiol, luteinizing hormone [LH], and follicle-stimulating hormone [FSH] in the postmenopausal range) - Patients 55 years old or younger must have biochemical evidence of definite postmenopausal status (defined as estradiol, LH, and FSH in the postmenopausal range) - Patients who have received prior luteinizing-hormone releasing-hormone (LHRH) analogues within the last year are eligible if they have definite evidence of postmenopausal status as defined above - Clinically adequate hepatic function - No bone fracture due to osteoporosis at any time during the 4-6 years of prior therapy - No prior or current malignancy except adequately treated basal cell or squamous cell carcinoma of the skin, in situ carcinoma of the cervix or bladder, or contra- or ipsilateral in situ breast carcinoma - No other nonmalignant systemic diseases (cardiovascular, renal, lung, etc.) that would prevent prolonged follow-up - No psychiatric, addictive, or any other disorder that compromises compliance with protocol requirements PRIOR CONCURRENT THERAPY: - See Disease Characteristics - More than 12 months since prior and no other concurrent endocrine SERM/AI therapy - Any type of prior adjuvant therapy allowed including, but not limited to, any of the following: - Neoadjuvant chemotherapy - Neoadjuvant endocrine therapy - Adjuvant chemotherapy - Trastuzumab (Herceptin®) - Ovarian ablation - Gonadotropin releasing hormone analogues - Lapatinib ditosylate - No concurrent hormone-replacement therapy, bisphosphonates (except for treatment of bone loss), or any other investigational agent