Trial results for the Phase 1 study (NCT04166734) investigating pembrolizumab in combination with hypofractionated stereotactic radiotherapy (SBRT) for patients with advanced malignant pleural mesothelioma were posted on ClinicalTrials.gov on 2026-02-04. The study reported no dose-limiting toxicities (DLTs) in the initial safety cohort of 5 participants.
Background
This study investigated pembrolizumab in patients with advanced malignant pleural mesothelioma. The trial focused on patients whose malignant pleural mesothelioma had progressed beyond first-line palliative chemotherapy, typically a platinum-based doublet, and who required further palliative systemic treatment or had declined first-line chemotherapy but were deemed suitable for it.
Trial design
The study (NCT04166734) was a Phase 1, multi-centre, non-randomized, open-label trial. It investigated pembrolizumab given in combination with SBRT to part of a pleural-based lesion. The trial enrolled 5 participants with advanced malignant pleural mesothelioma and was terminated. The study had originally planned to recruit up to 18 patients.
Key results
The trial reported safety and preliminary efficacy outcomes for the initial safety cohort. For the outcome of "Percentage of Patients With Dose Limiting Toxicity (DLT)", 0 Participants in the Initial Safety Cohort experienced a DLT.
Other key measurements from the Initial Safety Cohort included:
- Overall Response Rate: 1 Participant
- Disease Control Rate: 3 Participants
- Overall Survival (OS) at Six Months: 3 Participants
- Overall Survival (OS) at Twelve Months: 2 Participants
- Progression Free Survival at 6 Months: 2 Participants
For the "Expansion Cohort", reported outcomes included 0 Participants for Overall Response Rate, Disease Control Rate, and Overall Survival (OS) at Six Months.
Regarding "Worst Acute Toxicity Grade":
- Initial Safety Cohort: 3 Participants
- Initial Safety Cohort: 2 Participants
- Expansion Cohort: 0 Participants
What this means
The results from this Phase 1 trial suggest that pembrolizumab combined with SBRT for advanced malignant pleural mesothelioma did not lead to dose-limiting toxicities in the initial safety cohort. While preliminary efficacy data showed some responses and disease control in a very small number of participants, the trial was terminated with a limited enrollment of 5 participants. These early safety findings would typically inform further development, but the termination of the study indicates that further investigation in this specific trial design will not proceed.
Source
The information regarding these trial results was obtained from ClinicalTrials.gov, a public database of clinical studies. The results for study NCT04166734, titled "Pembrolizumab and Hypofractionated Stereotactic Radiotherapy in Patients With Malignant Pleural Mesothelioma," were posted on 2026-02-04 on clinicaltrials.gov.