• Primary endpoint met in first randomized Phase 2 study, FOURLIGHT-1, showing a 40% reduction in the risk of disease progression or death with manageable safety profile
  • More than 90% of patients initiated atirmociclib within 3 months of prior CDK4/6 inhibitor therapy
  • Results strengthen confidence in atirmociclib as a potential first-in-class, next-generation cell cycle inhibitor backbone for HR+, HER2- breast cancer and provide further support for development strategy in earlier lines of treatment

Pfizer Inc. (NYSE:PFE) today announced positive topline results from the randomized Phase 2 FOURLIGHT-1 study evaluating atirmociclib in combination with fulvestrant, versus fulvestrant or everolimus plus exemestane, in people with hormone receptor (HR)-positive, human epidermal growth factor receptor 2-negative (HER2-) advanced or metastatic breast cancer (MBC) who had received prior cyclin-dependent kinase (CDK) 4/6 inhibitor-based treatment. The study met its primary endpoint, demonstrating a statistically significant and clinically meaningful improvement in progression-free survival (PFS) as assessed by the investigator [HR: 0.60 (95% CI: (0.440, 0.825)), p=0.0007].

The PFS results were consistent across all prespecified subgroups, including performance status, menopausal status, presence of visceral disease, duration of treatment with prior CDK4/6 inhibitor (< or > 12 months), and regardless of prior CDK4/6 inhibitor received. More than 90% of patients initiated treatment with atirmociclib within three months of their last CDK4/6 inhibitor treatment. Overall survival (OS), a secondary endpoint, was not mature at the time of the analysis, with approximately 20% of participants having an event. These are the first randomized Phase 2 data in HR+ MBC for atirmociclib, an investigational, potential first-in-class CDK4 inhibitor.