Management of bone loss in postmenopausal breast cancer patients treated with aromatase inhibitors

Breast cancer is the most commonly diagnosed cancer among women, but despite survival rates improvement, it is still the second major cause of cancer related death. In postmenopausal women with estrogen receptor (ER) dependent breast cancer, hormone therapy is an option, either by direct inhibition of ER using tamoxifen or by aromatase inhibition, resulting in decreased estrogen production. In this paper these two endocrine therapy approaches are compared in terms of their impact on bone health. Guidance for the prevention of bone loss and occurrence of fractures in postmenopausal women receiving AIs is also proposed. Despite intervention strategies to maintain bone health in AI-treated patients are not well established, recommendations by international societies to identify women with high risk of fracture and advice on the preventive anti-fracture therapy are exposed. Finally, available therapeutic options for management of bone loss in patients receiving AIs are presented. The search strategy for this literature review was conducted by using the key words “aromatase inhibitor*” and “bone loss” OR “aromatase inhibitor*” and “osteoporosis” in the MEDLINE/PubMed database. Nowadays, hormone-responsive breast cancer in postmenopausal women is preferably being treated with AIs instead of tamoxifen, due to clear benefits in disease-free survival and reduced recurrence. AIs have an advantageous side effect profile compared to tamoxifen, however all AIs have detrimental long-term effects on bone, due to nearly complete depletion of estrogens, resulting in increased bone loss and increased risk of fracture. Current recommendations state that all women treated with AIs should be evaluated for their fracture risk prior to initiation of AI-treatment, taking in consideration individual bone mineral density and several risk factors. The thresholds to introduce preventive therapy and drugs proposed differ among the available recommendations. Lifestyle modifications and adequate calcium and vitamin D supplementation have been documented to have good impact in long-term bone health. Additionally, bisphosphonates are the first therapeutic option for AI induced bone loss and should be continued as long as AI-treatment is maintained, being iv zoledronic acid 4mg every 6 months the best tolerated option.