CDK inhibitor therapy after disease progression on a prior CDK inhibitor

The global, double-blind, placebo-controlled postMONARCH trial (NCT05169567), reported in abstract form, included 368 patients with HER2-negative ER-positive advanced breast cancer. Patients were randomly assigned in a 1:1 ratio to receive either abemaciclib plus fulvestrant or fulvestrant alone. Eligible patients had (1) disease progression during initial therapy for metastatic breast cancer, which included a CDK4/6 inhibitor and aromatase inhibitor (99% of patients), or (2) disease relapse during or after adjuvant therapy for early breast cancer with a CDK4/6 inhibitor plus endocrine therapy. The CDK inhibitor was palbociclib in 59% of patients, ribociclib in 33% of patients, and abemaciclib in 8% of patients. No other prior treatment was permitted for metastatic disease. The primary end point was investigator-assessed PFS.[25]

The global, double-blind, placebo-controlled postMONARCH trial (NCT05169567), reported in abstract form, included 368 patients with HER2-negative ER-positive advanced breast cancer. Patients were randomly assigned in a 1:1 ratio to receive either abemaciclib plus fulvestrant or fulvestrant alone. Eligible patients had (1) disease progression during initial therapy for metastatic breast cancer, which included a CDK4/6 inhibitor and aromatase inhibitor (99% of patients), or (2) disease relapse during or after adjuvant therapy for early breast cancer with a CDK4/6 inhibitor plus endocrine therapy. The CDK inhibitor was palbociclib in 59% of patients, ribociclib in 33% of patients, and abemaciclib in 8% of patients. No other prior treatment was permitted for metastatic disease. The primary end point was investigator-assessed PFS.[25]

The 6-month PFS rate was 50% in the abemaciclib-plus-fulvestrant group and 37% in the fulvestrant-alone group (HR, 0.73; 95% CI, 0.57–0.95).[25][Level of evidence B1]

The global, double-blind, placebo-controlled postMONARCH trial (NCT05169567), reported in abstract form, included 368 patients with HER2-negative ER-positive advanced breast cancer. Patients were randomly assigned in a 1:1 ratio to receive either abemaciclib plus fulvestrant or fulvestrant alone. Eligible patients had (1) disease progression during initial therapy for metastatic breast cancer, which included a CDK4/6 inhibitor and aromatase inhibitor (99% of patients), or (2) disease relapse during or after adjuvant therapy for early breast cancer with a CDK4/6 inhibitor plus endocrine therapy. The CDK inhibitor was palbociclib in 59% of patients, ribociclib in 33% of patients, and abemaciclib in 8% of patients. No other prior treatment was permitted for metastatic disease. The primary end point was investigator-assessed PFS.[25]

Overall response rate, a secondary end point, was 17% in the abemaciclib-plus-fulvestrant group and 7% in the fulvestrant-alone group.