The following is a summary of “Abemaciclib Plus Fulvestrant in Advanced Breast Cancer Following Progression on CDK4/6 Inhibition: Results from the Phase III postMONARCH Trial,” published in the December 2024 issue of Oncology by Kalinsky et al.
Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy (ET) are the standard first-line treatment for hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC), but progression occurs in nearly all patients.
Researchers conducted a prospective study assessing the effectiveness of abemaciclib + fulvestrant in people with HR+, HER2- ABC after disease progression on CDK4/6 inhibitors.
They randomized 368 people (abemaciclib+fulvestrant, n=182; placebo+fulvestrant, n=186) who had disease progression after prior CDK4/6 inhibitors plus aromatase inhibitors or after adjuvant therapy. The primary endpoint was progression-free survival (PFS), with secondary endpoints including PFS by blinded independent central review (BICR), objective response rate (ORR), and safety.
The results showed that abemaciclib + fulvestrant significantly improved investigator-assessed PFS compared to placebo + fulvestrant (HR, 0.73; 95% CI, 0.57-0.95; nominal P=0.017), with median PFS of 6.0 months (95% CI, 5.6-8.6) vs. 5.3 months (95% CI, 3.7-5.6), and a 6-month PFS rate of 50% vs. 37%. Results were further supported by BICR-assessed PFS (HR, 0.55; 95% CI, 0.39-0.77; nominal P<0.001). For people with measurable disease, the ORR was higher in the abemaciclib + fulvestrant group (17%) than placebo + fulvestrant (7%; nominal P=0.015). Safety findings were consistent with the known safety profile of abemaciclib.
They concluded that abemaciclib + fulvestrant significantly improved PFS after progression on prior CDK4/6 inhibitors in HR+, HER2- ABC, offering an additional treatment option for these people.
Source: ascopubs.org/doi/10.1200/JCO-24-02086
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