Bone-Targeted Agents and Metastasis Prevention

SIMPLE SUMMARY: Bone metastases are common in cancer patients and the role of bone-targeted agents in prevention of metastasis have been evaluated in multiple clinical trials over the past 20 years. Results show that in breast cancer the use of adjuvant bisphosphonates (and possibly denosumab) reduce bone metastases and breast cancer deaths in postmenopausal women. These effects are in addition to the benefits associated with the use of standard adjuvant endocrine, cytotoxic and targeted treatments with prevention of one in six breast cancer deaths at 10 years. Similar benefits have not been observed in other cancers that typically spread to bone, such as prostate or lung cancers. Biomarkers that can predict patient benefit from the use of bone targeted treatments in the adjuvant setting are being evaluated. Currently, tumour expression of the transcription factor, MAF, seems to be the most promising biomarker; benefits from adjuvant bisphosphonates are seen in the 80% of patients with normal levels of expression irrespective of menopausal status, while over-expression is associated with a poor prognosis and a higher rate of visceral metastases. ABSTRACT: The use of bone-targeted treatments has transformed the clinical care of many patients with metastatic breast cancer. In addition, due to the profound effects of bisphosphonates and denosumab on bone physiology and the bone microenvironment, the potential of bone-targeted agents to modify the process of metastasis has been studied extensively. Many adjuvant trials with bisphosphonates in early breast cancer have been performed. Variable outcomes in terms of disease recurrence have been reported, with any treatment benefits apparently influenced by the age and menopausal status of the patients. The Early Breast Cancer Trialists’ Collaborative Group (EBCTCG) conducted a meta-analysis of individual patient data from all available randomised trials to investigate this observation further. This meta-analysis failed to show any benefits of adjuvant bisphosphonates in premenopausal women, but highly significant improvements in bone recurrence (RR = 0.72; 95% CI 0.60–0.86, 2p = 0.0002) and breast cancer mortality (RR = 0.82; 95% CI 0.73–0.93, 2p = 0.002) were seen in the 11,767 postmenopausal women included in the meta-analysis. As a result, clinical guidelines recommend the incorporation of adjuvant bisphosphonates that inhibit osteoclast activity into routine clinical care. Denosumab, which has similar effects on bone cell physiology, appears not to consistently influence disease outcomes, perhaps suggesting that it is the “off target” effects of bisphosphonates on immune function and the biological processes involved in metastasis that are important. Predictive biomarkers beyond menopause are being sought and assessment of the transcription factor MAF (mesenchymal aponeurotic fibrosarcoma gene) appears to identify patients able to benefit from the addition of a bisphosphonate to standard adjuvant anticancer therapies.