Bone Density and Bone Loss in Postmenopausal Women With Breast Cancer Receiving Treatment in Clinical Trial IBCSG-1-98

DISEASE CHARACTERISTICS:

* Diagnosis of breast cancer

  * Resected disease
* Enrolled on protocol IBCSG-1-98

  * Receiving adjuvant endocrine therapy comprising 1 of the following regimens:

    * Letrozole
    * Tamoxifen
    * Letrozole after 2 years of tamoxifen
    * Tamoxifen after 2 years of letrozole
  * Not yet completed 5 years of treatment
* No breast cancer recurrence or second primary cancer
* No known, symptomatic bone disease, including osteomalacia or osteogenesis imperfecta
* No prior registration to protocol IBCSG-1-98 Bone Mineral Density substudy
* Hormone receptor status:

  * Estrogen receptor-positive and/or progesterone receptor-positive tumor

PATIENT CHARACTERISTICS:

* Female
* Postmenopausal
* No uncontrolled thyroid or parathyroid disease, Cushing's disease, or other pituitary diseases
* No malabsorption syndrome or clinically relevant vitamin D deficiency
* No patients for whom the bone density determination is impossible

PRIOR CONCURRENT THERAPY:

* See Disease Characteristics
* More than 1 year since prior and no concurrent anticonvulsants
* More than 6 weeks since prior and no concurrent corticosteroids (at doses \> the equivalent of 5 mg/day prednisone) for \> 2 weeks total
* No prior or concurrent sodium fluoride (at daily doses ≥ 5 mg/day) for \> 1 month
* More than 12 months since prior and no concurrent anabolic steroids
* More than 6 months since prior treatment, either investigational or not, for the prevention of osteoporosis (excluding calcium or cholecalciferol \[vitamin D\])
* No concurrent raloxifene
* Concurrent therapeutic intervention for osteoporosis comprising bisphosphonates allowed
* Concurrent warfarin allowed provided it is given for ≤ 4 weeks