Trastuzumab Deruxtecan for ERBB2-Mutant Metastatic Non–Small Cell Lung Cancer With or Without Brain Metastases: A Secondary Analysis of Randomized Clinical Trials

Importance Brain metastases reduce overall survival rates of patients with non–small cell lung cancer (NSCLC); patients with epidermal growth factor receptor 2 (ERBB2 [formerly HER2])–mutant NSCLC are more likely to have baseline brain metastases. Trastuzumab deruxtecan (T-DXd) is an approved ERBB2-directed treatment for previously treated unresectable or metastatic ERBB2-mutant NSCLC.<br> Objective To assess the clinical effectiveness and safety of T-DXd 5.4 mg/kg and 6.4 mg/kg doses in patients with previously treated ERBB2-mutant metastatic NSCLC with or without untreated or previously treated stable brain metastases.<br> Design, Setting, and Participants This post hoc secondary analysis pooled patients from the DESTINY-Lung01 (data cutoff date: December 3, 2021) and DESTINY-Lung02 (data cutoff date: December 23, 2022) clinical trials by T-DXd dose (5.4 mg/kg and 6.4 mg/kg). DESTINY-Lung01 was a multicenter, open-label, 2-cohort, nonrandomized phase 2 study, while DESTINY-Lung02 was a dose-blinded, multicenter, 2-cohort, randomized phase 2 study. Participants had a previously treated ERBB2-mutant metastatic NSCLC with or without untreated or previously treated stable brain metastases at baseline. All statistical analyses were performed from April 2023 to October 2024.<br> Intervention Patients received a T-DXd dose of either 5.4 mg/kg or 6.4 mg/kg intravenously every 3 weeks.<br> Main Outcome and Measure Systemic and intracranial effectiveness by blinded independent central review using RECIST (Response Evaluation Criteria in Solid Tumors) version 1.1, sites of progression, and safety.<br> Results This analysis included 102 patients in the T-DXd 5.4-mg/kg dose group (65 females [64%]; median [range] age, 57.5 [37.0-83.0] years and 59.5 [30.0-79.0] years in patients with and without brain metastases, respectively) and 141 patients in the T-DXd 6.4-mg/kg dose group (94 females [67%]; median [range] age, 62.5 [29.0-88.0] years and 59.0 [27.0-83.0] years in patients with and without brain metastases, respectively). In each group, 31% (32 of 102) and 38% (54 of 141) of patients, respectively, had baseline brain metastases and 53% (17 of 32) and 44% (24 of 54), respectively, received prior brain metastasis treatment. In patients with and without brain metastases, systemic confirmed objective response rates (ORRs) were 47% (15 of 32; 95% CI, 29%-65%) and 50% (35 of 70; 95% CI, 38%-62%), respectively, with the T-DXd 5.4-mg/kg dose, and 50% (27 of 54; 95% CI, 36%-64%) and 59% (51 of 87; 95% CI, 48%-69%) with the T-DXd 6.4-mg/kg dose. Median progression-free survival was 7.1 (95% CI, 5.5-9.7) months in the T-DXd 5.4-mg/kg dose group and 7.1 (95% CI, 4.5-9.6) months in the T-DXd 6.4-mg/kg dose group of patients with baseline brain metastases. Among patients with measurable baseline brain metastases, intracranial confirmed ORRs were 50% (7 of 14; 95% CI, 23%-77%) with the T-DXd 5.4-mg/kg dose and 30% (9 of 30; 95% CI, 15%-49%) with the T-DXd 6.4-mg/kg dose. At both doses, the safety profile of T-DXd was generally manageable, regardless of baseline brain metastases, favoring the T-DXd 5.4 mg/kg dose.<br> Conclusions and Relevance In this secondary analysis, T-DXd at the approved dose of 5.4 mg/kg showed antitumor activity in patients with previously treated ERBB2-mutant metastatic NSCLC with or without brain metastases. This finding supports T-DXd 5.4 mg/kg use in this population.