Study to Assess Efficacy of Risedronate in Preventing Bone Loss in Postmenopausal Women Treated for Breast Cancer

Inclusion Criteria: * Postmenopausal women (more than one year since last menstrual period or removal of ovarian function by surgical or radiotherapic means) * Operated for an invasive breast cancer (histologically proven) * Surgical treatment completed and cycles of adjuvant chemotherapy (if necessary) completed * Treated with aromatase inhibitor * Osteopenic (-2.5\<T score\<-1) without osteoporotic fracture * With written informed consent signed * With social security Exclusion Criteria: * Women presenting a history of osteoporotic fracture or a T score less than -2.5 at at least one measure site * Women presenting clinical signs of metastases * Having received other hormonal treatment in the last 3 months * Having received treatment by bisphosphonates, raloxifene, tamoxifen, parathormone, strontium ranelate, tibolone,calcitonin and corticosteroids at more than 5mg/d for 3 months in the last year * Presenting a known and untreated hyperthyroid * Presenting a known hyperadrenocorticism * Patients treated and followed for Paget's disease of bone * Presenting a untreated primary hyperparathyroid * Presenting an indication against risedronate (known hypersensibility to risedronate monosodium and/or one of its excipients, non-corrected hypocalcemia, pregnancy or breast feeding, severe renal insufficiency inferior to 30 ml/min) * Patients presenting malabsorption syndrome for glucose/galactose * Person participating in another clinical trial concerning a medicine susceptible to influence bone mass