Abstract PO3-04-01: Population Pharmacokinetics of trastuzumab deruxtecan (T-DXd) in HER2-positive breast cancer subjects: analyses across 12 Phase 1-3 studies

Abstract Background: T-DXd, an antibody-drug conjugate composed of a humanized anti-HER2 monoclonal antibody and a topoisomerase I inhibitor payload, is approved for adult patients with unresectable or metastatic HER2-positive (HER2+) BC administered T-DXd 5.4 mg/kg Q3W with a prior anti-HER2–based therapy either in the metastatic setting, or in the neoadjuvant or adjuvant setting and have developed disease recurrence during or within six months of completing therapy. The objective of this analysis was to present pharmacokinetic (PK) characterization of T-DXd and DXd in patients with advanced/metastatic HER2-positive breast cancer from a pooled data source of 12 phase 1 to 3 clinical trials. Methods: Data from subjects with HER2-positive breast cancer and other solid tumors enrolled in studies DS8201-A-J101, DS8201-A-J102, DS8201-A-A103, DS8201-A-A104, DS8201-A-U201, DS8201-AJ202, DS8201-A-U205, DS8201-A-U204, DS8201-A-U206, DS8201-A-U301, DS8201-A-U302, and DS8201-A-U303 were used for this analysis. A population PK (PopPK) analysis was performed using nonlinear mixed effects modeling approach using NONMEM® (version 7.4.3). The effect of significant covariates was evaluated by univariate and multivariate analyses on steady-state exposure of T-DXd and DXd. Results: Data across T-DXd doses 0.8 to 8 mg/kg with 2216 subjects were included. The PK of T-DXd and DXd were adequately described by PopPK analysis based on standard model diagnostic techniques. T-DXd elimination clearance and volume of distribution of central and peripheral compartments were estimated at 0.402 L/day, 2.68 L and 5.91 L, respectively. DXd elimination clearance was estimated at 18.4 L/hour. Covariates previously detected to be statistically significant (cancer type, tumor size, albumin, race-country, body weight and sex for T-DXd; age, cancer type, AST, total bilirubin, ritonavir or itraconazole use, race-country, formulation and body weight for DXd) were retained in the PopPK model. No new covariates were identified as statistically significant in the PopPK analysis. All covariates were contained within the 0.8 to 1.25 exposure ratio interval in T-DXd and DXd steady-state area under the concentration-time curve (AUC), indicating no clinically meaningful effect, except for subjects with high body weight (90 kg; 95th percentile) showing a 28% and 26% higher T-DXd and DXd AUC, respectively, relative to a BC subject with median body weight of 60 kg. None of these changes were clinically meaningful based on exposure-response analyses of efficacy and safety endpoints. T-DXd and DXd post hoc exposure estimates in all BC subjects (HER2-positive and HER2-low) as well as BC subjects with HER2- positive were comparable across hepatic function, renal function, region, race-country and line of therapy. Conclusions: Similar T-DXd and DXd exposures were obtained for the recommended dosing of 5.4 mg/kg Q3W T-DXd in BC subjects across categories of hepatic function, renal function, region, race-country, HER2 status, and line of therapy. Citation Format: Claire Li, Stefanie henning, Kashyap Patel, Katrina Hui, Gerly van der Vleuten, malaz Abutarif, Tushar Garimella, Amit Khatri. Population Pharmacokinetics of trastuzumab deruxtecan (T-DXd) in HER2-positive breast cancer subjects: analyses across 12 Phase 1-3 studies abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-04-01.