Inclusion Criteria

DISEASE CHARACTERISTICS:

- Diagnosis of localized breast cancer

- Stage I-IIIA disease

- Adequately treated breast cancer

- No clinical or radiological evidence of recurrent or metastatic disease

- Baseline total lumbar spine or femoral neck bone mineral density T-score < -2.0
standard deviation (e.g., a patient with a T score of -2.1 is eligible)

- Hormone-receptor status:

- Estrogen receptor and/or progesterone receptor-positive breast cancer

PATIENT CHARACTERISTICS:

- Female

- Postmenopausal, defined by 1 of the following criteria:

- Age > 55 years with cessation of menses

- Age ≤ 55 years with spontaneous cessation of menses for > 1 year

- Age ≤ 55 years with spontaneous cessation of menses for ≤ 1 year, but
amenorrheic (e.g., spontaneous or secondary to hysterectomy), AND has
postmenopausal estradiol levels

- Bilateral oophorectomy

- ECOG performance status 0-2

- Life expectancy ≥ 5 years

- WBC ≥ 3,000/mm³ OR granulocyte count ≥ 1,500/mm³

- Platelet count ≥ 100,000/mm³

- Alkaline phosphatase ≤ 3 times upper limit of normal (ULN)

- AST ≤ 3 times ULN

- Creatinine < 2.0 mg/dL

- Creatinine clearance ≥ 45 mL/min

- No hypercalcemia (i.e., calcium level > 1 mg/dL above ULN) OR hypocalcemia (i.e.,
calcium level > 0.5 mg/dL below lower limit of normal) within the past 6 months

- No other malignancy within the past 5 years except adequately treated basal cell or
squamous cell skin cancer or carcinoma in situ of the cervix

- No other nonmalignant systemic diseases, including any of the following:

- Uncontrolled infection

- Uncontrolled diabetes mellitus

- Uncontrolled thyroid dysfunction

- Disease affecting bone metabolism (hyperparathyroidism, hypercortisolism,
Paget's disease, osteogenesis imperfecta)

- Malabsorption syndrome

- No uncontrolled seizure disorders associated with falls

- No known hypersensitivity to zoledronate or other bisphosphonates, letrozole,
calcium, or vitamin D

- No concurrent active dental problems, including any of the following:

- Infection of the teeth or jawbone (maxillary or mandibular)

- Dental or fixture trauma

- Prior or current diagnosis of osteonecrosis of the jaw

- Exposed bone in the mouth

- Slow healing after dental procedures

- No contraindication to spine dual energy x-ray absorptiometry (DXA) as defined by any
of the following:

- History of surgery at the lumbosacral spine, with or without implantable devices

- Scoliosis with a Cobb angle > 15 degrees at the lumbar spine

- Immobility, hyperostosis, or sclerotic changes at the lumbar spine, or evidence
of sclerotic abdominal aorta sufficient to interfere with DXA scan

- Disease of the spine that would preclude the proper acquisition of a lumbar
spine DXA

- No condition that would preclude study follow-up or compliance

- No psychiatric illness that would preclude giving informed consent

PRIOR CONCURRENT THERAPY:

- More than 3 weeks since prior and no other concurrent oral bisphosphonates

- No prior intravenous bisphosphonates

- No prior aromatase inhibitor therapy

- More than 6 months since prior anabolic steroids or growth hormone

- More than 2 weeks since prior and no concurrent inhibitor of osteoclastic bone
resorption (e.g., calcitonin, mithramycin, or gallium nitrate)

- More than 30 days since prior systemic investigational drug and/or device

- More than 7 days since prior topical investigational drug

- More than 6 weeks since prior and no concurrent dental or jaw surgery (e.g.,
extraction, implants)

- Concurrent short-term corticosteroid therapy allowed

- No concurrent sodium fluoride, parathyroid hormone, or tibolone

- No other concurrent investigational drug or device