Impact Of Abemaciclib On The Time To Subsequent Chemotherapy And The Time To Second Disease Progression Across The Monarch 2 And 3 Studies

1048Background: Abemaciclib is a selective oral inhibitor of CDK4 u0026 6 dosed on a twice-daily continuous schedule. Abemaciclib was an effective treatment with a generally tolerable safety profile in combination with fulvestrant (F) (MONARCH 2) and as initial therapy (MONARCH 3) when combined with a nonsteroidal aromatase inhibitor (NSAI) in patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer. To evaluate the impact of abemaciclib in subsequent treatment, we analyzed time to subsequent chemotherapy (TCT) and time to second disease progression (PFS2). Methods: Enrollment criteria and study designs of MONARCH 2 and 3 were previously reported (Sledge et al., 2017; Goetz et al., 2017). Exploratory analyses were performed to assess TCT and PFS2 using the Kaplan-Meier (KM) method. Hazard ratios (HR) were estimated using a Cox model. TCT was defined as time from randomization (R) to time to first chemotherapy (CT). Since exact progression date on post-t...