ESG401, a trophoblast cell-surface antigen 2 (TROP2) antibody drug conjugate (ADC), for the treatment of first-line metastatic triple negative breast cancer (mTNBC).
Authors: Fei Ma, Fuming Qiu, Zhongsheng Tong, Yehui Shi, Guohua Yu, Xinhong Wu, Hong Wang, Jiani Wang, Hua Yang, Anwen Liu, Yan Zhang, Hongmei Zheng, Qiongyu Lan, Yongqiang Zhang, Ying Cheng, Qing Zhou, Xiaoyan Xing, Xiaomei Chen
Journal: Journal of Clinical Oncology (2024)

e13132 Background: ESG401, a novel ADC comprising a humanized anti-TROP2 IgG1 monoclonal antibody conjugated to the Topoisomerase I Inhibitor SN-38, with the Drug-Antibody Ratio at 8, by a stable cleavable linker, exhibited preliminary efficacy and tolerability in the Phase Ia trial (Ma, ASCO 2023). This report summarizes current results from the first-line mTNBC cohort of the Phase Ib trial. Methods: Patients (pts) aged ≥18 years with confirmed local advanced/unresectable or metastatic TNBC, without prior metastatic treatment, received ESG401 (16 mg/kg IV on Day 1,8, and 15, with a 28-day cycle) until unacceptable toxicity, progressive disease, or consent withdrawal. Results: As of the cutoff date (Jan 30 th , 2024), 23 pts in the cohort received ≥1 dose of ESG401. Median age was 52 years (range: 33-73), 34.8% were ECOG 0, 26.1% were de novo stage IV, 73.9% had visceral disease (8.7% brain, 34.8% liver, 52.2% lung), 43.5% received radiotherapy, and 73.9% received chemotherapy (73.9% Taxanes, 69.6% Anthracycline, 4.3% Platinum)as prior treatments for early-stage disease. Among 14 Efficacy Evaluable (EE) pts, the ORR was 78.6%, including one (7.1%) patient who achieved a complete response. DCR was 100%, and CBR was 85.7%. Eight pts (57.1%) achieved confirmed Partial Response (PR). As of the cutoff date, 14 pts (63.6%) remained on treatment, with the longest on-treatment duration being 8.0 mons. Two (2) pts in this cohort had brain metastases. One pt achieved a complete intracranial response, and the overall response evaluation was PR. The evaluation time for the other pt has not yet been reached. Across the entire Phase Ia/1b trials, including 15 EE pts with brain metastases, the best overall intracranial response rate was 33%, with an intracranial disease control rate of 73%. The response of the intracranial tumor lesion is correlated with the response of the non-CNS lesion. The safety profile of ESG401 remained consistent with previous reports, showing no new or unexpected safety signals. The most common TRAEs were leukopenia (65.2%), neutropenia (69.6%), anemia (43.5%), fatigue (21.7%), nausea (43.5%), and vomiting (34.8%). The most common TRAEs≥ Grade 3 were neutropenia (43.5%). There was no ≥ Grade 3 diarrhea. No interstitial lung disease (ILD) has been reported so far for the entire PhIa/b trials containing 139 pts. Conclusions: ESG401 demonstrates promising antitumor activity in the first-line mTNBC pts, with efficacy comparable to the combination therapy reported by the BEGONIA Study. Additionally, the efficacy of ESG401 in brain metas in the first-line mTNBC pts is in alignment with our previous observations made in the late-line mTNBC and HR+/HER2- BC pts. These results warrant further clinical investigation of ESG401. Clinical trial information: NCT04892342 .