Effectiveness of Zoledronic Acid in the Prevention of Osteoporosis in Early Breast Cancer Patients Receiving Letrozole

Inclusion Criteria:

* Postmenopausal women with histologically documented early (non-metastatic) breast cancer
* Previous treatment with tamoxifen for at least 2.5 years and not more than 3.5 years
* Assigned to receive letrozole treatment
* Karnofsky performance status ≥ 70
* Life expectancy ≥ 16 weeks
* Signed informed consent after full explanation of study by participating clinician and prio to any study specific procedures
* Adjuvant or neoadjuvant chemotherapy is allowed
* No clinical and/or radiologic evidence of distant metastases
* No prior treatment with an aromatase inhibitor
* Able to comply with treatment and scheduled follow-up visits
* Age between 18 and 82 years

Exclusion Criteria:

* Pregnant or lactating women or women with child bearing potential
* Patients with other malignancies except except adequately treated basal cell carcinoma of the skin or in-situ cervix carcinoma
* Active infection or other serious underlying medical condition which would impair the ability of the patient to receive protocol treatment
* Clinical and/or radiological evidence of distant metastases.
* Evidence of pathological fracture
* Prior treatment with an aromatase inhibitor
* Prior administration of any intravenous bisphosphonate during the last year.
* Oral bisphosphonate must be discontinued within 4 weeks of enrollment
* Administration of long-term systemic corticosteroids within the last 12 months (short term steroid treatment is allowed.)
* Prior use of parathyroid hormone treatment for more than 1 week
* Use of any drug known to affect the skeleton (calcitonin, mithramycin, gallium nitrate) within two weeks prior to enrollment
* Abnormal renal function: creatinine clearance must be above 30 ml/min (calculated by Cockroft formula)
* Evidence of metabolic bone disease( Paget's, osteogenesis imperfecta, hyperparathyroidism within the 12 months prior to enrollment)
* Baseline lumbar spine and or total hip Bone Mineral Density T score below -2
* Known hypersensitivity to zoledronic acid
* Psychological, familial, sociologic, or geographic conditions which do not permit medical follow-up and compliance with the study protocol
* White blood cell ≤ 3.0 x 10exp9 /L or granulocytes ≤ 1.5 x 10exp9/L or platelets ≤100 x 10exp9
* Total bilirubin\> 1.5 x upper normal limit, SGOT and SGPT \> 2.5 x upper normal limit
* Unable to undergo DXA bone density scanning (spine deformity, severe scoliosis, lumbar sacral spine surgery)