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A Pilot Study of Pembrolizumab Combined With Stereotactic Ablative Radiotherapy for Patients With Advanced or
Jeremy P Harris1, Jino Park1, Eric Ku1
1Department of Radiation Oncology, University of California Irvine, Orange, CA, USA.
Objectives:
Immunotherapy with immune checkpoint inhibitors has shown only limited success in the management of metastatic soft tissue sarcoma. Overall response rates (ORR) with single agent pembrolizumab were 18% and median PFS was 18 weeks on the clinical trial SARC028. One strategy to improve the responses to immunotherapy is with stereotactic body radiation therapy (SBRT), which can enhance the antitumor CD8 T cell response through the release of tumor-specific antigens, potentially priming a more diverse class of T cell receptors.
Methods:
This is a phase 0, pilot prospective study taking place at a single center with 2 arms. In Arm A, patients are treated with pembrolizumab 400 mg IV infusion on day 1 of a 42-day cycle. Stereotactic body radiation therapy (SBRT) is delivered in 1-5 fractions starting on C1D15-28 and given every other day. In Arm B, patients who have started an immune checkpoint inhibitor within 60 days are treated with SBRT in addition to the current therapy.
Results:
In this study we outline testing the feasibility of adding SBRT to pembrolizumab.
Conclusion:
The ultimate goal of combination therapy is improved overall response, including tumors not treated with SBRT. This trial can be found registered online: NCT05488366.
Insights
This pilot study explores combining stereotactic body radiation therapy (SBRT) with pembrolizumab to improve responses in metastatic soft tissue sarcoma patients. The goal is to enhance immunotherapy effectiveness beyond the treated tumor site.
Area of Science:
- Oncology
- Immunotherapy
- Radiation Oncology
Background:
- Metastatic soft tissue sarcoma (STS) has limited response rates to single-agent immunotherapy like pembrolizumab (18% ORR, 18-week PFS).
- Stereotactic body radiation therapy (SBRT) may enhance immunotherapy by releasing tumor antigens and boosting CD8 T cell responses.
- Combining SBRT with immune checkpoint inhibitors (ICIs) is a strategy to improve clinical outcomes in STS.
Purpose of the Study:
- To test the feasibility of combining SBRT with pembrolizumab in patients with metastatic STS.
- To evaluate the potential of combination therapy to improve overall response rates, including abscopal effects.
Main Methods:
- A phase 0, pilot prospective single-center study with two arms.
- Arm A: Patients receive pembrolizumab (400 mg IV) every 42 days, with SBRT delivered in 1-5 fractions starting between C1D15-28.
- Arm B: Patients already on an ICI receive SBRT in addition to their current therapy.
Main Results:
- This study outlines the feasibility testing of adding SBRT to pembrolizumab treatment.
- Results focus on the procedural and safety aspects of the combination therapy.
Conclusions:
- The combination of SBRT and pembrolizumab aims to improve overall response in metastatic STS.
- The ultimate goal is to achieve enhanced responses in both irradiated and non-irradiated tumors.
- Clinical trial registration: NCT05488366.
