Importance of the field: Breast cancer is one of the leading causes of cancer-related deaths in the world. Despite the significant improvements in the adjuvant treatment strategies of early-stage breast cancer, many patients experience relapse. Bisphosphonates are widely used in the treatment of bone metastasis of solid tumors and multiple myeloma, as well as in osteoporosis. The results of clinical studies of adjuvant treatment on earlystage hormone-receptor-positive breast-cancer patients under hormonal treatment - especially with the bisphosphonate zoledronic acid - caused excitement because they demonstrated an additive effect on decreasing disease relapses at bone or other sites. A number of clinical and in vitro and in vivo preclinical studies, which are either ongoing or have just ended, are investigating the mechanisms and antitumoral activity of bisphosphonates.