Impact of Dose Reduction on Efficacy: Implications of Exposure-Response Analysis of Palbociclib
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ORIGINAL RESEARCH ARTICLE
Impact of Dose Reduction on Efficacy: Implications of Exposure‑Response Analysis of Palbociclib Jenny Zheng1 · Yanke Yu2 · Chandrasekar Durairaj2 · Véronique Diéras3 · Richard S. Finn4 · Diane D. Wang2
© The Author(s) 2020
Abstract Background Palbociclib is indicated for hormone receptor–positive, human epidermal growth factor receptor 2–negative advanced breast cancer (ABC). Objective Exposure-response analyses were conducted to evaluate efficacy in Asian versus non-Asian patients and in patients with versus without dose reduction in PALOMA-2. Patients and Methods PALOMA-2 compared palbociclib plus letrozole versus placebo plus letrozole in patients with ABC. Population pharmacokinetic analysis provided apparent palbociclib clearance (CL/F) for each patient. The time-varying exposure metric, Cavg,t, was calculated using average dose intensity and CL/F at the time of each progression-free survival (PFS) event. A Cox proportional model characterized PFS and palbociclib Cavg,t relationships. Significant prognostic factors for PFS were identified by univariate analysis, which were subsequently included in multivariate analyses, in addition to the Cavg,t effect on PFS. PFS profiles in Asian/non-Asian patients and patients with/without dose reduction were simulated and compared using observed palbociclib exposures and established exposure-response relationships. Results Patients (n = 421) received palbociclib plus letrozole (Asian = 64, non-Asian = 357; no dose reduction = 272, dose reduction = 149). Based on univariate analyses, significant prognostic factors were Ki67 score, age, and baseline aspartate aminotransferase (BAST), tumor size, alkaline phosphatase, and albumin levels. In multivariate analysis, only Ki67 and BAST remained significant. Palbociclib exposure did not significantly affect PFS in either univariate (P = 0.12) or multivariate (P = 0.44) analyses. Conclusions This analysis suggests that palbociclib exposure has no impact on PFS when the dose reduction algorithm from palbociclib clinical trials is used. There is no difference in efficacy between Asians and non-Asians, despite the higher level of dose reductions in Asians. Pfizer NCT01740427. Key Points Palbociclib dose reduction does not affect efficacy of the drug. Although Asian patients experienced greater dose reduction, palbociclib efficacy was not compromised. * Jenny Zheng [email protected] 1
Pharmacometrics, Global Product Development, Pfizer Inc, Col-D/006/D6400, 500 Arcola Rd., Collegeville, PA 19426, USA
2
Clinical Pharmacology, Global Product Development, Pfizer Inc, San Diego, CA, USA
3
Department of Medical Oncology Institut Curie, Paris and Centre Eugène Marquis, Rennes, France
4
David Geffen School of Medicine at UCLA, Santa Monica, CA, USA
1 Introduction Breast cancer is the most common cancer among women worldwide, with ∼ 2.1 million cases reported in 2018 [1]. Treatment choice for breast cancer is decided based on several factors, including the status of hormone (estrog
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