The data demonstrated clinically meaningful efficacy and a manageable safety profile for trastuzumab pamirtecan monotherapy across all HER2 immunohistochemistry (“IHC”) expression levels (IHC1+, IHC2+, IHC3+)ii. Outcomes were consistent among patients regardless of prior checkpoint inhibitor treatment. The data will be presented today in an oral session at the 2026 Society of Gynecologic Oncology (“SGO”) Annual Meeting on Women’s Cancers in San Juan, Puerto Rico.
“Endometrial cancer is one of the few cancers with an increasing mortality rate,1 and there is an urgent need for new treatment options, especially for patients with recurrent disease with lower HER2 expression levels where current standard-of-care chemotherapy offers only a 15 % response rate2,” said Bhavana Pothuri, M.D., Medical Director of the Clinical Trials Office (CTO) and Director of Gynecologic Oncology Research at the NYU Langone Perlmutter Cancer Center. “We are encouraged by these results for trastuzumab pamirtecan, which showed clinically meaningful responses across all HER2 levels. Importantly, these results were seen in a broad patient population that reflects real-world clinical practice, including patients who have received prior immune checkpoint inhibitor treatment and those with visceral metastases.”
The analysis of the Phase 2 cohort included 145 patients with advanced or metastatic HER2-expressing endometrial cancer whose disease had progressed following first- or later lines of therapy. This cohort met its primary efficacy endpoint of objective response rate (“ORR”) evaluated in 73 patients previously treated with checkpoint inhibitor therapy and confirmed HER2 status by central testing, showing a confirmed ORR of 49.3% (95% CI: 37.4, 61.3). In all centrally tested patients (n=96) the confirmed ORR was 47.9% (95% CI: 37.6, 58.4) with a median progression-free survival (“mPFS”) of 8.1 months (95% CI: 5.5, 11.8).
Among the 143 efficacy-evaluable patients by locali HER2 status testing, the confirmed ORR was 44.1% (95% CI: 35.8, 52.6). Trastuzumab pamirtecan consistently demonstrated encouraging antitumor activity across all HER2 expression levels, with comparable results whether HER2 testing was conducted locally or centrally. Among patients with local HER2 testing, the confirmed ORR was 33.9% (IHC1+) and 40.4% (IHC2+) in patients with lower levels of HER2 expression, and 73.1% (IHC3+) in patients with higher HER2 expression levels. The median duration of response (“mDoR”) was 10.3 months. mPFS for all evaluable patients (n=145), whether they had received prior checkpoint inhibitor treatment or not, was 8.0 months (95% CI: 5.6, 8.3).
The safety profile was manageable and as expected for HER2-targeted ADCs. The most common treatment-related adverse events (TRAEs) were low-grade nausea, anemia, platelet count decrease, and low-grade fatigue. Grade ≥3 treatment-related adverse events (TRAEs) were reported in 68 of 145 (46.9%) patients. Adjudicated cases of interstitial lung disease (“ILD”) or pneumonitis of grade ≥3 occurred in 4.8% of patients and were consistent with the known safety profile of HER2-targeted ADC therapies. The majority of events grade 3 or higher were efficiently manageable with appropriate medical interventions.
“These positive results in patients with endometrial cancer including those with lower HER2 expression levels support the potential of trastuzumab pamirtecan,” said Prof. Özlem Türeci, M.D., Co-Founder and Chief Medical Officer at BioNTech. “HER2 remains an important therapeutic target, particularly in gynecologic cancers and breast cancer. 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 tumors.”
Trastuzumab pamirtecan received Fast Track and Breakthrough Therapy designations from the U.S. Food and Drug Administration (“FDA”) for the treatment of endometrial cancer in 2023. A global confirmatory Phase 3 clinical trial Fern-EC-01 (NCT06340568) evaluating trastuzumab pamirtecan monotherapy compared to chemotherapy in previously treated patients with HER2-expressing, recurrent endometrial cancer is ongoing. BioNTech and DualityBio plan to file a biologics license application (“BLA”) in 2026, subject to regulatory feedback from the FDA.
About trastuzumab pamirtecan
Trastuzumab pamirtecan (BNT323/DB-1303) is a third-generation topoisomerase-1 inhibitor-based ADC targeting HER2 and is being developed by BioNTech and Duality Biologics. Trastuzumab pamirtecan was built from DualityBio’s proprietary Duality Immune Toxin Antibody Conjugates (“DITAC”) platform. HER2 is a surface-expressed protein on solid tumors and has been linked to the aggressive growth and spread of cancer cells. Preclinical data and preliminary clinical data for trastuzumab pamirtecan indicate its potential to target HER2 receptors on solid tumors irrespective of expression level with a manageable safety profile and a potentially expanded therapeutic window.
Trastuzumab pamirtecan is being evaluated in an ongoing Phase 1/2 trial (NCT05150691) in patients with advanced/metastatic solid tumors, and in two global Phase 3 clinical trials. Fern-EC-01, a randomized Phase 3 clinical trial (NCT06340568) evaluating trastuzumab pamirtecan compared with investigator's choice of single agent chemotherapy in previously treated patients with HER2-expressing advanced recurrent endometrial cancer, is currently enrolling patients. DYNASTY-Breast02, a Phase 3 clinical trial (NCT06018337) evaluating trastuzumab pamirtecan in patients with Hormone Receptor-positive (“HR+”) and Human Epidermal Growth Factor Receptor 2 (“HER2”)-low, metastatic breast cancer that have progressed on hormone and/or cyclin-dependent kinase 4/6 (“CDK4/6”) therapy, is fully enrolled and expected to read out this year.
About the Phase 1/2a trial
The global, multi-cohort Phase 1/2a clinical trial (NCT05150691) evaluated the safety and tolerability of trastuzumab pamirtecan in patients with advanced solid tumors that express HER2. Cohort 2b is a Phase 2 expansion cohort which enrolled 145 patients with advanced/metastatic HER2-expressing endometrial cancer whose disease had progressed after first- and later lines of therapy. The HER2 status was determined for all patients through local testing and, where possible, confirmed via central testing. The primary endpoints were objective response rate in patients with prior checkpoint inhibitor treatment with HER2 expression, confirmed by retrospective central testing, and safety. Secondary endpoints included ORR, DoR, DCR, PFS and OS.
i Central testing refers to HER2 expression level analysis performed at a single, designated laboratory, whereas local testing refers to analysis performed at a patient’s individual trial site or local laboratory.
ii HER2 immunohistochemistry (“IHC”) expression levels: IHC1+ = low expression, IHC2+ = moderate expression, IHC3+ = high expression
1 National Cancer Institute. Cancer Stat Facts: Uterine Cancer. https://seer.cancer.gov/statfacts/html/corp.html. Accessed March 17, 2026.
2 Makker V, et al. J Clin Oncol. 2023 Apr 14;41(16):2904–2910.
