• Whitney P Kirschbrown, Matts Kågedal, Bei Wang, Lars Lindbom, Adam Knott, Rachelle Mack, Sharareh Monemi, Ihsan Nijem, Sandhya Girish, Christie Freeman, Debora Fumagalli, Robin McConnell, Guy Jerusalem, Chris Twelves, José Baselga, Gunter von Minckwitz, José Bines, and Amit Garg.
• Genentech, 1 DNA Way, South San Francisco, CA, 94080, USA.
• Cancer Chemother. Pharmacol. 2019 Jun 1; 83 (6): 1147-1158.

PurposeTo characterize the pharmacokinetics (PK) of, and perform an exploratory exposure-response (E-R) analysis for, pertuzumab in patients with HER2-positive early breast cancer (EBC) within the APHINITY study (NCT01358877, BIG 4-11/BO25126/TOC4939G).MethodsA previously developed pertuzumab two-compartment linear population pharmacokinetic (popPK) model was subjected to external validation to examine appropriateness for describing pertuzumab concentrations from the APHINITY study. Pharmacokinetic drug-drug interactions (DDIs) between pertuzumab, trastuzumab, and chemotherapy were assessed by comparing observed serum or plasma Cmax, Cmin, and AUClast geometric mean ratios with 90% CIs. Predictions of pertuzumab Cmax,ss, Cmin,ss, and AUCss were derived from individual parameter estimates and used in an exploratory E-R analysis.ResultsUsing data from 72 patients, based on goodness-of-fit, the popPK model was deemed appropriate for predictions of individual exposures for subsequent comparisons to historical data, assessment of DDIs, and E-R analyses. No evidence of DDIs for pertuzumab on trastuzumab, trastuzumab on pertuzumab, or pertuzumab on chemotherapy PK was observed. Analyses of differences in exposure between patients with and without invasive disease-free survival events did not indicate improved efficacy with increased exposure. Overall Grade ≥ 3 diarrhea prevalence was higher with pertuzumab versus placebo, but was not greater with increasing pertuzumab exposure. No apparent E-R relationship was suggested with respect to other grade ≥ 3 AEs.ConclusionOverall, the limited available data from this exploratory study suggest that no dose adjustments are needed for pertuzumab when administered in combination with trastuzumab and an EBC chemotherapy regimen.

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