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

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