Our findings showed that palbociclib, a protein kinase inhibitor, was strongly associated with neutropenia and granulocytopenia but weakly associated with febrile neutropenia, neutropenic colitis, neutropenic sepsis, and neutropenic infection, with asymptomatic neutropenia being considered the main adverse effect of palbociclib. This evidence concerns the gene WEE1 and Decreased total neutrophil count.