Several important studies were presented at the 2015 ASCO Annual Meeting in the field of breast cancer. Austrian Breast and Colorectal Study Group trial 18 again indicated the importance of bone health in postmenopausal women receiving endocrine therapy and showed that denosumab, a monoclonal antibody targeting the RANK ligand, was highly active in the reduction of fracture rates in this population. In the metastatic setting, addition of palbociclib to fulvestrant nearly tripled progression-free survival in pretreated women with luminal breast cancer as shown in the randomized phase III PALOMA-3 trial. In HER2-positive breast cancer, results from a randomized phase II study suggested that T-DM1 with or without endocrine therapy may be a valuable option as neoadjuvant treatment. In this trial, pathologic complete remission rates of > 40 % were observed after only four cycles of T-DM1. The phase III ExteNET study evaluated the role of neratinib, a tyrosine-kinase inhibitor targeting HER2 and epidermal growth factor receptor, as extended adjuvant therapy after 1 year of trastuzumab; while the future role of neratinib remains still undefined, this was the first study to show an improvement in terms of disease-free survival over the current treatment standard. Finally, the MARIANNE trial showed that T-DM1 was as effective as trastuzumab plus docetaxel as first-line therapy, while dual HER2-inhibition with T-DM1 plus pertuzumab yielded no further benefit.