• Richard S Finn, Katalin Boer, Igor Bondarenko, Ravindranath Patel, Tamas Pinter, Marcus Schmidt, Yaroslav V Shparyk, Anu Thummala, Nataliia Voitko, Eustratios Bananis, Lynn McRoy, Keith Wilner, Xin Huang, Sindy Kim, Dennis J Slamon, and Johannes Ettl.
• David Geffen School of Medicine, University of California Los Angeles, 2825 Santa Monica Blvd, Suite 200, Santa Monica, CA, USA. RFinn@mednet.ucla.edu.
• Breast Cancer Res. Treat. 2020 Sep 1; 183 (2): 419-428.

PurposePalbociclib is a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, approved in combination with endocrine therapy for the treatment of women and men with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer (HR+/HER2- ABC). In the phase 2, open-label, PALOMA-1 trial, palbociclib plus letrozole significantly prolonged progression-free survival (PFS) versus letrozole alone (hazard ratio, 0.488; 95% CI 0.319‒0.748; P = 0.0004; median PFS, 20.2 vs 10.2 months, respectively) in postmenopausal women with estrogen receptor-positive (ER+)/HER2- ABC. Here, we present the final overall survival (OS) and updated safety results.MethodsPostmenopausal women with ER+/HER2- ABC were randomized 1:1 to receive either palbociclib (125 mg/day, 3/1 schedule) plus letrozole (2.5 mg/day, continuous) or letrozole alone (2.5 mg/day, continuous). The primary endpoint was investigator-assessed PFS; secondary endpoints included OS and safety.ResultsA total of 165 patients were randomized. At the data cutoff date of December 30, 2016 (median duration of follow-up, 64.7 months), the stratified hazard ratio for OS was 0.897 (95% CI 0.623-1.294; P = 0.281); median OS in the palbociclib plus letrozole and letrozole alone arms was 37.5 and 34.5 months, respectively. The median time from randomization to first subsequent chemotherapy use was longer with palbociclib plus letrozole than letrozole alone (26.7 and 17.7 months, respectively). The most frequently reported adverse event in the palbociclib plus letrozole arm was neutropenia (any grade, 75%; grade 3 or 4, 59%).ConclusionsPalbociclib plus letrozole treatment led to a numerical but not statistically significant improvement in median OS. Pfizer Inc (NCT00721409).

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