Abstract
Background: Trastuzumab emtansine (T-DM1) is an antibody–drug conjugate composed of trastuzumab, the cytotoxic agent DM1, and a stable thioether linker. The effects of T-DM1 exposure on safety in patients with HER2-positive locally advanced or MBC are reported. Methods: The exposure–safety analysis included 618 patients with pharmacokinetic (PK) data who received single-agent T-DM1 3.6 mg/kg q3w from five phase 2 or 3 studies: TDM4258g, TDM4374g, TDM4450g/BO21976, TDM4688g, and EMILIA. Exposure parameters observed in cycle 1 were T-DM1 conjugate AUC, T-DM1 conjugate Cmax, and DM1 Cmax, (no PK accumulation). Safety endpoints were worst grade of thrombocytopenia (TCP) or hepatotoxicity (HPT) by protocol definitions. A multivariate logistic regression analysis was conducted to evaluate the association of exposure and clinically relevant covariates with the probability of experiencing TCP or HPT. Platelet counts (PLT), alanine transaminase (ALT), aspartate transaminase (AST), and total bilirubin (TBL) versus time profiles were also evaluated by exposure quartiles to further test exposure effect on lab values. A secondary analysis for patients in the EMILIA study alone (n=307) was also conducted. Results: Grade ≥3 TCP and grade≥ 3 HPT were observed in 72 patients and 45 patients in the exposure–safety data set, respectively. Data from the pooled studies showed no statistically significant association between exposure and the incidence of grade ≥3 TCP (T-DM1 AUC P=0.99, T-DM1 Cmax P=0.97, DM1 Cmax P=0.72), or grade ≥3 HPT (T-DM1 AUC P=0.25, T-DM1 Cmax P=0.93, DM1 Cmax P=0.95). Additionally, no obvious difference was observed for longitudinal PLT, ALT, AST, or TBL profiles across exposure quartiles, with no exposure–safety relationship for the probability that PLT, ALT, AST, or TBL exceeded grade 3 thresholds. Similar results were observed for the EMILIA analysis. Conclusions: For patients with HER2-positive locally advanced or MBC treated with T-DM1 3.6 mg/kg q3w, no exposure–safety relationship was observed for TCP, HPT, PLT, or liver function based on T-DM1 or DM1 exposure.