Lynce F, Blackburn MJ, Zhuo R, et al. - This single-arm, open-label, investigator-initiated study (PALINA) was undertaken to determine the hematologic safety of palbociclib (a cyclin-dependent kinase 4/6 inhibitor) in African American females suffering from hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (ABC). These patients with a baseline absolute neutrophil count ≥1000/mm ³ were administered palbociclib (125 mg daily; 21 days on and 7 days off) plus endocrine therapy. Febrile neutropenia or permanent study cessation due to neutropenia did not occur. Occurrence of grade 3 and 4 neutropenia as well as necessity for a palbociclib dose reduction were found in significantly more patients with the Duffy null vs the wild-type variant. Lower overall relative dose intensity and a lower clinical benefit rate were seen in patients with the Duffy null vs the wild-type variant. Findings indicated the good tolerability of palbociclib in African American women with HR-positive/HER2-negative ABC. There may exist an impact of Duffy null status on the incidence of grade 3 neutropenia, dose intensity, and possibly on clinical benefit.