FOURLIGHT-1
What it tests: Atirmociclib plus fulvestrant in HR+/HER2− advanced or metastatic breast cancer following progression on a prior CDK4/6 inhibitor. Randomized phase 2 study.
4Sight: FOURLIGHT-1
All ESMO 2026 4Sights
In brief
OncoAlert 4Sight, #ESMO2026
Efficacy and Safety of Atirmociclib + Fulvestrant in Patients With HR+/HER2– Advanced/Metastatic Breast Cancer Who Progressed on Prior CDK4/6 Inhibitor in a Randomized Phase 2 Study (FOURLIGHT-1)
Randomized phase 2 (n=263): atirmociclib + fulvestrant vs investigator’s choice (fulvestrant or everolimus + exemestane) in HR+/HER2– mBC after prior CDK4/6i. Primary: investigator-assessed PFS.
Median PFS 9.4 vs 6.6 mo; HR 0.60 (0.440–0.825); 1-sided p=0.0007
ORR in patients with measurable disease: 19.3% vs 11.3%; CBR: 61.9% vs 46.0%
Atirmociclib discontinuation due to TRAEs: 4.0%; most common TRAE neutropenia (46.4%)
First next-generation CDKi to show significant and clinically meaningful PFS improvement after prior CDK4/6i, with a manageable safety profile.
Antonio Giordano