Evidence of increased toxicity (i.e. including neutropenia, increased alanine transaminase, diarrhea, and anemia) in the ASCO trial was reported with 24% of patients discontinuing treatment, confirming that dose-limiting toxicity of myelosuppression is consistent with the on-target inhibition of CDK4/6 inhibitors [45]. Here, CDK4 is linked to Decreased total neutrophil count.