CDK9 and neoplasm: Treatment with 17.5 mg/kg the CDK9 inhibitor for 20 days plus 5 Gy of radiation once on day 4 (Figure 4A) reduced PDX tumor volumes by 67% compared with radiation alone (p = 0.016) and by 48% compared with the CDK9 inhibitor alone (p = 0.062) (Figure 4B and 4C).