Trial results for the Phase 1/2 study (NCT03272334) investigating pembrolizumab in combination with HER2 BATs for patients with metastatic breast cancer were posted on ClinicalTrials.gov on 2026-02-27. The study reported a low incidence of dose-limiting toxicities (DLTs), with only 1 participant experiencing a DLT across all evaluated schedules in the Phase 1 portion.
Background
The study, titled "Her2-BATS and Pembrolizumab in Metastatic Breast Cancer," investigated the combination of HER2Bi armed activated T-cells (HER2 BATs) and pembrolizumab (also known as Keytruda) in women with metastatic breast cancer (MBC).
Trial design
The PHASE1/PHASE2 study (NCT03272334) enrolled 22 participants diagnosed with metastatic breast cancer. The trial aimed to determine a safe dose of the combination of pembrolizumab and HER2 BATs in Phase 1, followed by further evaluation of safety and preliminary efficacy in Phase 2. The interventions included HER2 BATs using an established schedule and pembrolizumab (200 mg per dose).
Key results
The trial reported on dose-limiting toxicities (DLTs) and overall survival.
- For "Dose Limiting Toxicities (Escalation and Expansion Cohorts)":
- In Phase 1: Schedule #1, 0 participants experienced DLTs.
- In Phase 1: Schedule #2, 1 participant experienced DLTs.
- In Phase 1: Schedule #3, 0 participants experienced DLTs.
- In Phase 2: Schedule #3, 0 participants experienced DLTs.
- For "Dose Limiting Toxicities on the Selected Arm in the Expansion Cohort," across all schedules (Phase 1: Schedule #1, Phase 1: Schedule #2, Phase 1: Schedule #3, and Phase 2: Schedule #3), 0 participants experienced DLTs.
Overall Survival (OS) was also measured:
- For Phase 1: Schedule #1, the mean OS was 687 days (Standard Deviation: 224 days).
- For Phase 1: Schedule #2, the mean OS was 677 days (Standard Deviation: 547 days).
- For Phase 1: Schedule #3, the mean OS was 547 days (Standard Deviation: 406 days).
- For Phase 2: Schedule #3, the mean OS was 405 days (Standard Deviation: 339 days).
What this means
The results from this Phase 1/2 study indicate that the combination of pembrolizumab and HER2 BATs demonstrated a favorable safety profile in patients with metastatic breast cancer, with a low number of dose-limiting toxicities observed across the evaluated schedules. The overall survival data provides preliminary insights into the duration of response in this patient population. These findings support further investigation into this combination therapy.
Source
The information regarding these trial results was obtained from ClinicalTrials.gov, a public database of clinical studies. The results for study NCT03272334, titled "Her2-BATS and Pembrolizumab in Metastatic Breast Cancer," were posted on 2026-02-27 on clinicaltrials.gov.