Hoste G, et al. - In postmenopausal women with highly pretreated endocrine therapy-resistant metastatic breast cancer (MBC), researchers tested palbociclib, a first-in-class cyclin-dependent kinase 4 and 6 inhibitor. For the efficacy and safety analysis, they included 82 patients who had taken at least one dose of palbociclib and who, at the data cut-off point, had at least 6-months follow-up. Findings revealed that treatment with palbociclib in combination with endocrine therapy provided an surprisingly high clinical benefit rate and demonstrated favorable safety profile in heavily pretreated endocrine-resistant estrogen receptor-positive, HER2-negative MBC patients.