Mabwell said Phase II data showed 9MW2821 produced a 30% response rate among patients with ADC-pretreated triple-negative breast cancer, findings it plans to present at the European Society for Medical Oncology (ESMO) Congress.
The analysis covered 60 patients with locally advanced or metastatic triple-negative breast cancer (TNBC) who had previously received an antibody-drug conjugate (ADC) carrying a topoisomerase I inhibitor payload. Mabwell set April 10, 2026, as the data cutoff and reported an objective response rate of 30.0%.
The company also reported an 80.0% disease control rate, median progression-free survival of 3.7 months and median duration of response of 8.7 months. Median overall survival had not matured by the cutoff. Mabwell said its safety monitoring had identified no additional signals; the announcement did not give adverse-event counts.
9MW2821 is a Nectin-4-targeting ADC also known as Bulumtatug Fuvedotin (BFv). Mabwell’s Phase II trial description assigns the drug alone to the previously ADC-treated group, while a separate cohort of patients who had not received prior systemic therapy receives it with a PD-1 inhibitor. The reported Phase II results do not compare 9MW2821 with another treatment.
Mabwell has said it is pursuing the approach because chemotherapy remains the main treatment after patients progress on topoisomerase I-payload ADCs. Separately, a first-in-human Phase I/II study published in Annals of Oncology reported a 50% objective response rate and an 80% disease control rate among 20 TNBC patients in the 1.25 mg/kg dose group. That was a different cohort, and the study did not establish whether those patients had received a topoisomerase I-payload ADC, so the results are not directly comparable.
Mabwell announced May 29 that the first patient had been dosed in a Phase III TNBC trial. The randomized, open-label study compares 9MW2821 with investigator-selected chemotherapy in patients previously treated with taxane-based chemotherapy and an ADC carrying a topoisomerase inhibitor payload.
Mabwell plans to present the Phase II findings orally at the ESMO Congress in Madrid, scheduled for Oct. 23-27.
