It is important to note that due to differences in how palbociclib is metabolized due to genetic variants of Cytochrome P450 Family 3 Subfamily A Member 4 (CYP3A4) and Sulfotransferase Family 2A Member 1 (SULT2A1) in certain patients, Asian patients in particular are more likely to experience serious neutropenia [25]. The gene discussed is SULT2A1; the disease is neutropenia.