Real-world multicenter study of T-DXd treatment in Chinese patients with metastatic breast cancer

Background: Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate (ADC) approved in China for HER2-positive or HER2-low metastatic breast cancer (MBC) patients. Little real-world evidence is available in China. This study aimed to investigate the real-world effectiveness and safety of T-DXd in Chinese MBC patients. Methods: This study retrospectively enrolled 309 MBC patients treated with T-DXd across 9 institutions nationwide in China between December 2019 and March 2024. T-DXd was administered intravenously at a dose of 5.4 mg/kg on day 1 of a 21-day cycle. Real-world progression-free survival (rwPFS) and overall survival (OS) were estimated using the Kaplan-Meier method. Real-world adverse events (AEs) were graded according to CTCAE 4.0. The study was registered at ClinicalTrials.gov (NCT05594082). Findings: A total of 309 MBC patients were included, with 168 HER2-positive and 141 HER2-negative patients (133 of HER2-low and 8 of HER2 0). Among HER2-positive and HER2-negative patients, median age was 53.5 and 55.0 years, 14.3% and 17.7% ECOG scores of 2, 83.9% and 84.4% patients with visceral metastases, 32.7% and 23.4% patients with brain metastasis, respectively. The median number of lines of therapy (LOT) for MBC patients receiving T-DXd was 4 for both groups. At the cutoff date of 30 July 2024, in patients with HER2-positive MBC, median rwPFS and OS was 12.1 [95% confidence interval (CI): 8.5-14.7] and 22.7 months (95% CI: 16.6-28.8). The longer rwPFS, median 23.3 months, was observed in LOT 1-2, than 12.2 months in LOT 3-5 and 8.2 months in LOT≥6 (P=0.001). In patients with HER2-negative MBC, median rwPFS and OS was 7.7 (95% CI: 6.6-8.8) and 15.7 months (95% CI: 11.4-20.0). The median rwPFS for HR+ and HR- patients was 7.7 and 8.1 months, respectively (P=0.870). Longer rwPFS of 9.5 months was observed in LOT 1-4 compared to 6.4 months in LOT≥6 among HER2-negative patients (P=0.026). Patients with prior ADCs exposure showed significantly shorter rwPFS of T-DXd in both HER2-positive (P=0.032) and negative patients (P=0.039). Brain metastasis did not impact the effectiveness of T-DXd. Incidence of AEs of any grade was 69.3% and severe (grade 3 or above) AEs was 13.9%; no fatal AEs were observed. Interstitial lung disease (ILD) occurred in 23 patients (7.4%), with 15 (4.9%) of grade 1, 4 (1.3%) of grade 2, and 4 (1.3%) of grade 3. 80.7% of ILD patients, including all with grade 1 and one with grade 2, underwent a rechallenge with T-DXd after symptomatic treatments and careful evaluations. Interpretation: In this largest dataset of T-DXd for Chinese patients with MBC to date, encouraging rwPFS of T-DXd was seen in heavily pretreated HER2-positive and HER2-negative MBC patients. Longer rwPFS was observed in MBC patients with fewer LOT and no prior ADC exposure. Meanwhile, T-DXd showed a manageable toxicity profile in understudied real-world patients. Rechallenge of T-DXd is feasible following effective symptomatic treatments and comprehensive assessments of ILD severity and recovery. Funding: This work was supported by grants from Beijing Science and Technology Innovation Medical Development Foundation (KC2022-ZZ-0091-4).