BMC Cancer 2009, 9:154 http://www.biomedcentral.com/1471-2407/9/154 BPs zoledronate and pamidronate. There is preclinical data showing that zoledronate is much more potent than other BPs. However, this has not been confirmed in clini- cal settings. Clinically, the choice among the various N- BPs is dependent on the adherence of patients and prefer- ence of clinicians [11]. Conclusion We conclude that BP treatment may give a survival benefit in metastatic breast cancer patients, particularly in patients with HR negative tumors, which are known to have a poorer prognosis. We believe that this analysis adds insight into the roles of BPs in metastatic breast can- cer, in addition to their ancillary role in supportive care. Based on these results, new strategies could be investi- gated for the possible benefits of BP treatment in meta- static breast cancer patients without bone involvement. Abbreviations HR: hormone receptor; BPs: bisphosphonates; N-BPs: nitrogen containing bisphosphonates; OS: overall sur- vival; DFI: disease free interval; MBD: metastatic bone dis- ease; SREs: skeletal related events; TTP_BD: time to progression of bone disease; IHC: immunohistochemis- try; FISH: fluorescent in situ hybridization; RANKL: recep- tor activator of the nuclear factor-κB ligand; TRAIL: tumor necrosis factor-related apoptosis-inducing ligand. Competing interests The authors declare that they have no competing interests. Authors' contributions IHP and JR designed the study and conducted the data acquisition. IHP and BHN performed the statistical analy- sis. IHP, JR and BHN participated in the interpretation of the data. IHP and JR drafted and revised the manuscript. IHP, JR, BHN, YK and KSL participated in critical review of the manuscript. All authors read and approved the final manuscript. Acknowledgements This study was supported by NCC Grant No-0610240. References 1. 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