These preclinical studies have prompted the clinical testing of AZD4573 in hematologic malignancies (Rule et al. 2018; Barlaam et al. 2020) and suggest that H3K27M-mutant tumors that are characterized by AFF4 upregulation are candidates for clinical CDK9 inhibition (Barlaam et al. 2020). Here, CDK9 is linked to hematologic disorder.