Breast cancer has a significant capacity to metastasize to bone. Bisphosphonates are the standard treatment for hypocalcaemia of malignancy (HCM), which is a common complication of bone metastasis. The combination of bisphosphonates with standard anticancer drugs such as paclitaxel or tamoxifen results in a synergistic apoptotic effect greater than that produced by either single agent alone. Potential antitumour effects in vitro of the two bisphosphonates zoledronic acid (Zol) and ibandronate (Ib) (each at 30 µM) combined with different anticancer drug combinations: cyclophosphamide/metotrexate/5-fluorouracil (CMF), epirubicin/cyclophosphamide (EC), epirubicin/paclitaxel (ET), and epirubicin/docetaxel (EDoc) were investigated using ATP-cell viability assay (ATP-CVA). Twenty cases of female primary, invasive breast cancer were assessed. Ibandronate and zoledronic acid alone showed an inhibitory effect on breast cancer tumour cells in vitro. The breast tumour growth inhibition effect for those two drugs amounted to 22 and 25% respectively. Inhibitory effects were clearly visible for all four combinations of anticancer drugs together with both bisphosphonates. Combinations of anticancer drugs with zoledronic acid seem to be more effective with respect to tumour growth inhibition than combinations with ibandronate.

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