Consistent with the safety profile of other CDK4/6 inhibitors with similar potencies for CDK4 and CDK6 (palbociclib and ribociclib) [22–24], the most frequent grade 3 or 4 AEs of dalpiciclib were neutropenia and leukopenia, observed in 52.5 and 35.0% of patients respectively. The gene discussed is CDK6; the disease is neutropenia.