Regarding individual CDK4/6i therapies, grade 3 or 4 neutropenia was observed in 23% (7/31) of patients receiving abemaciclib, 41% (11/27) of those on ribociclib, and 30% (3/10) of those on palbociclib (Figure 6C-D and Table S5 in Multimedia Appendix 1). Here, CDK4 is linked to Decreased total neutrophil count.