[Toxicity of Palbociclib in Patients Aged 70 Years and Older with Metastatic Breast Cancer].

We aimed to examine palbociclib toxicity in patients aged 70 years and older with metastatic breast cancer(MBC). From December 2017 to August 2018, 32 patients with estrogen receptor(ER)-positive, human epidermal growth factor receptor 2(HER2)-negative MBC were included in this study. The most common adverse event(AE)observed was neutropenia, and comparative rates of grade 3 or 4 AE were identified in the groups of patients aged ≥70 years(n=11)and <70 years(n=21) (91% vs 81%). Febrile neutropenia occurred in one patient. Although dose interruption rate was higher in the older group (≥70 years of age)than in the younger group(<70 years of age)(100% vs 86%, respectively), reduction rates were similar between the two groups(64% vs 62%, respectively). Palbociclib was well-tolerated in Japanese older(≥70 years of age) MBC patients.