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

Letrozole is an aromatase inhibitor used in the treatment of hormone receptor positive metastatic breast cancer in postmenopausal women.It has more recently been approved for use in many countries as adjuvant therapy for early breast cancer; and is often used in an adjuvant regimen following 2-3 years of tamoxifen treatment or as an extended adjuvant therapy after up to 5 years of tamoxifen. Letrozole inhibits the conversion of androgens to estrogens in vitro and in vivo. Plasma levels of estradiol and related estrogen compounds in postmenopausal patients receiving letrozole are suppressed up to 95% from baseline and are often undetectable.The estrogen deprivation in women receiving letrozole may cause increased bone resorption and bone loss.Studies comparing tamoxifen and aromatase inhibitors, in adjuvant therapy have shown an increase fracture rate, and decreased bone mineral density in patients receiving aromatase inhibitors. Zoledronic acid is an intravenously administered bisphosphonate that inhibits osteoclastic bone resorption. Intravenous bisphosphonates are effective in reducing the rate of skeletal complications, including fractures, in patients with metastatic breast cancer and other tumors when given every few weeks. Small clinical trials have given some evidence that osteoporosis can be effectively treated by one or two doses of intravenous zoledronic acid per year. This study will determine the effect of giving zoledronic acid every 6 months on the bone mineral density of patients receiving letrozole as adjuvant therapy for early breast cancer after having received adjuvant tamoxifen for at least 2.5 years. Patients will be randomized to receive zoledronic acid either at the start of letrozole therapy or when bone mineral density T score drops below - 2 standard deviation or at the occurrence of a non-trauma related fracture.