Inclusion Criteria

DISEASE CHARACTERISTICS:

- Diagnosis of breast cancer

- Stage I, II, or IIIA disease

- Completed ≤ 6 years of adjuvant tamoxifen therapy

- Total baseline lumbar spine or femoral neck bone mineral density T-score below -2.0
standard deviation (e.g., a patient with a T-score of -2.1 in ineligible; a patient
with a T-score of -1.9 is eligible)

- No clinical or radiological evidence of recurrent or metastatic disease

- Hormone receptor status:

- Estrogen receptor- and/or progesterone receptor-positive

PATIENT CHARACTERISTICS:

Age

- Postmenopausal

Sex

- Female

Menopausal status

- Postmenopausal, defined by 1 of the following:

- Over 55 years of age with cessation of menses

- 55 years of age and under with spontaneous cessation of menses for > 1 year

- 55 years of age and under with spontaneous cessation of menses for ≤ 1 year, but
amenorrheic (e.g., spontaneous or secondary to hysterectomy) with postmenopausal
estradiol levels (< 5 ng/dL)

- Undergone bilateral oophorectomy

Performance status

- ECOG 0-2

Life expectancy

- At least 5 years

Hematopoietic

- WBC ≥ 3,000/mm^3

- Platelet count ≥ 100,000/mm^3

Hepatic

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

- AST ≤ 3 times ULN

Renal

- Creatinine < 2.0 mg/dL

- No hypercalcemia (i.e., calcium > 1 mg/dL above ULN within the past 6 months)

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

Other

- No uncontrolled infection

- No uncontrolled diabetes mellitus

- No uncontrolled thyroid dysfunction

- No disease affecting bone metabolism (e.g., hyperparathyroidism, hypercortisolism,
Paget's disease, or osteogenesis imperfecta)

- No malabsorption syndrome

- No uncontrolled seizure disorder associated with falls

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

- No mental illness that would preclude giving informed consent

- 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 non-malignant systemic disease

- No clinical or radiologic evidence of existing fracture in the lumbar spine and/or
total hip

- No history of fracture with low intensity or not associated with trauma

- No contraindication to spinal dual energy x-ray absorptiometry (DEXA) due to any of
the following:

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

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

- Immobility, hyperostosis, or sclerotic changes at the lumbar spine

- Evidence of sufficient sclerotic abdominal aorta that would interfere with DEXA
scan

- Any disease of the spine that would preclude proper acquisition of a lumbar
spine DEXA

- Considered reliable

PRIOR CONCURRENT THERAPY:

Biologic therapy

- Not specified

Chemotherapy

- No concurrent chemotherapy

Endocrine therapy

- See Disease Characteristics

- Prior parathyroid hormone allowed provided it was not administered for > 1 week

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

- More than 12 months since prior endocrine therapy (including estrogen) except for the
following:

- Tamoxifen

- Insulin

- Oral hypoglycemics

- Thyroid hormone

- Steroid inhalers

- More than 12 months since prior systemic corticosteroids except short-term
corticosteroids to prevent or treat chemotherapy-induced nausea and vomiting or acute
respiratory illness

- Concurrent short-term corticosteroids allowed

- No other concurrent hormonal therapy

- No concurrent parathyroid hormone

Radiotherapy

- Not specified

Surgery

- Not specified

Other

- Prior systemic sodium fluoride allowed provided it was not administered for > 3
months within the past 2 years

- More than 3 weeks since prior oral bisphosphonates

- More than 2 weeks since prior and no concurrent drugs known to affect the skeleton
(e.g., calcitonin, mithramycin, or gallium nitrate)

- More than 30 days since prior systemic investigational drugs and/or devices

- More than 7 days since prior topical investigational drugs

- No prior IV bisphosphonates

- No prior aromatase inhibitor therapy

- No concurrent calcitonin, sodium fluoride, or Tibolone

- No other concurrent anticancer therapy

- No other concurrent bisphosphonates

- No other concurrent investigational drugs or devices