BioNTech and DualityBio reported encouraging data from a Phase II cohort of their global clinical study evaluating the efficacy of trastuzumab pamirtecan (BNT323/DB-1303) in treating advanced endometrial cancer expressing human epidermal growth factor receptor 2 (HER2).
This cohort is part of a Phase I/IIa trial designed to assess both the safety and tolerability of the antibody-drug conjugate (ADC) trastuzumab pamirtecan across various solid tumours.
Essential primary endpoints, including objective response rate and safety, were measured, particularly focusing on patients with confirmed HER2 status through retrospective central testing.
Secondary endpoints collected data on disease control rates, progression-free survival, and overall survival.
The Phase II cohort analysis included 145 patients whose conditions had progressed following initial chemotherapy, with or without previous checkpoint inhibitor therapy.
Trastuzumab pamirtecan, a third-generation topoisomerase-1 inhibitor-based therapy, showed a tolerable safety profile for patients at all levels of HER2 expression.
The primary efficacy endpoint was met, with a confirmed objective response rate of 49.3% among 73 patients who had previously received checkpoint inhibitor therapy and had their HER2 status centrally confirmed.
Across all centrally tested patients, the response rate was 47.9%, with a median progression-free survival of 8.1 months.
Results from 143 patients tested locally for HER2 status revealed a confirmed response rate of 44.1%, showing consistent antitumor activity across various expression levels.
Notably, higher HER2 expression correlated with a more considerable response rate, such as 73.1% in Immunohistochemistry Score 3+ (IHC3+) patients. The median duration of response across the cohort was 10.3 months.
BioNTech co-founder and chief medical officer Professor Özlem Türeci said: “These positive results in patients with endometrial cancer, including those with lower HER2 expression levels, support the potential of trastuzumab pamirtecan.
“We are continuing to advance trastuzumab pamirtecan, both as a monotherapy and in novel-novel treatment combination approaches, with the aim to address the significant unmet medical needs in the treatment of patients with HER2-driven tumours.”
Common side effects that were observed were mild nausea, anaemia, decreased platelet counts, and fatigue.
More serious adverse events of grade 3 or higher affected 46.9% of patients, with interstitial lung disease or pneumonitis occurring in 4.8% of cases.
BioNTech and DualityBio anticipate submitting a biologics licence application this year, contingent upon feedback from the US Food and Drug Administration (FDA).
In December 2025, Bristol Myers Squibb and BioNTech’s pumitamig displayed promising efficacy and safety during a mid-stage trial in front and second-line triple-negative breast cancer.
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