Treatment patterns and clinical outcomes among patients receiving palbociclib in combination with an aromatase inhibitor or fulvestrant for HR+/HER2-negative advanced/metastatic breast cancer in real-world settings in the US: Results from the IRIS study

Abstract Purpose Palbociclib is a selective cyclin-dependent kinase (CDK) 4/6 inhibitor approved for use in postmenopausal women with hormone receptor-positive, human epidermal growth factor 2-negative (HR+/HER2-) advanced/metastatic breast cancer (ABC/MBC). Palbociclib has proven benefits in phase III placebo-controlled studies; however, real-world outcome data are lacking. The Ibrance Real World Insights (IRIS) study evaluated palbociclib use in patients with HR+/HER2- ABC/MBC in the real-world setting in the US, Argentina, and Germany. Here we describe results for the US patient subgroup. Patients and methods IRIS was a retrospective medical chart review study of patients with confirmed HR+/HER2- ABC/MBC who received palbociclib with either an aromatase inhibitor (AI) as initial endocrine-based therapy in postmenopausal women or fulvestrant-based therapy in women with disease progression following endocrine therapy. Physicians extracted data from patient medical records for ≤16 sequential patients each. Outcomes included progression-free and survival rates. Results Records were extracted for 652 patients: 360 (55.2%) treated with palbociclib + AI and 292 (44.8%) treated with palbociclib + fulvestrant. The 12-month progression-free rate was 84.1% for patients treated with palbociclib + AI and 79.8% for those treated with palbociclib + fulvestrant; 12-month survival rates were 95.1% for palbociclib + AI and 87.9% for palbociclib + fulvestrant. Conclusion In this first real-world assessment of clinical outcomes in US patients with HR+/HER- ABC/MBC, treatment with palbociclib in combination with AI or fulvestrant demonstrated favorable effectiveness in terms of progression-free and survival rates. Ongoing studies are needed to deliver mature clinical outcome data beyond 12/24 months in the real-world setting.