Real-world clinical outcomes and toxicity in metastatic breast cancer patients treated with palbociclib and endocrine therapy

Purpose Real-world data are critical to demonstrate the reproducibility of evidence and external generalizability of randomized clinical trials. Palbociclib is an oral small-molecule inhibitor of cyclin-dependent kinases 4 and 6 that has been shown to improve progression-free survival (PFS) when combined with letrozole or fulvestrant in phase 3 clinical trials. We evaluated real-world outcomes in metastatic breast cancer patients who received palbociclib in combination with endocrine therapy in routine clinical practice.