HOBOE: A Phase 3 Study of Adjuvant Triptorelin and Tamoxifen, Letrozole, or Letrozole and Zoledronic Acid in Premenopausal Patients With Breast Cancer.

Inclusion Criteria: * Histological diagnosis of breast cancer * Surgical resection of breast cancer (breast conserving surgery or mastectomy) * No evidence of disease * Indication for adjuvant hormonal therapy (ER and/or PgR positive with IHC exam in at least 1% of primary tumor cells, according to St. Gallen criteria) * Patient age at least 18 years * Written informed consent . Premenopausal status defined as LMP within 12 months of randomization (FSH, LH will not be considered as determinants of menopausal status due the chemotherapy induced reversible ovarian suppression) Please note that patients who have received neoadjuvant or adjuvant chemotherapy and/or locoregional radiation therapy may be included in the study Exclusion Criteria: * Performance status (ECOG)\>2. * Previous or concomitant malignancy (with the exception of adequately treated nonmalignant skin cancer and carcinoma in situ of the uterine cervix * Metastatic breast cancer * Creatinine \> 1.25 times the value of upper normal limit * Pregnant or lactating females * Clinical or radiologic evidence of bone fractures * Treatment with systemic cortisone therapy within 12 months prior to randomization * Treatment with drugs that could alter bone metabolism (calcitonin, mithramycin, gallium nitrate) within 2 weeks prior to randomization * Previous treatment with tamoxifen or aromatase inhibitors * AST and/or ALT \> 3 times the value of upper normal limit with clinical and laboratory findings that indicate a grade of hepatic insufficiency that could potentially increase the risk of assuming letrozole * Any concomitant conditions that would, in the Investigator's opinion, contraindicate the use of any of the drugs used in this study * Inability to provide informed consent * Inability to comply with followup * Patient undergoing invasive dental work at time of baseline evaluation or foreseen during the course of adjuvant therapy