CDK4 and neutropenia: However, some TEAEs occurred at a higher frequency in the Japanese subpopulation compared with the overall population [13], including a higher incidence of grade 2 and 3 (but not grade 4) neutropenia and leukopenia, Similar to this finding, a higher frequency of hematological toxicities was previously observed in the Japanese subpopulation of the global phase 3 study of another CDK4 and CDK6 inhibitor, palbociclib, in women with HR + , HER2- ABC, with a higher incidence of ≥ grade 3 neutropenia in Japanese patients treated with palbociclib compared with the overall study population [9].