Summary: Patients with recurrent high-grade astrocytoma — an aggressive and often fatal form of brain cancer — historically face a median survival of roughly four to five months. A new Phase 1/2b clinical trial, however, reports a dramatic improvement in outcomes by combining laser interstitial thermal therapy (LITT) with the immune checkpoint inhibitor pembrolizumab.
LITT uses focused laser heat to destroy tumor tissue while temporarily disrupting the blood-brain barrier (BBB). That temporary opening appears to allow cancer-fighting T-cells and immunotherapy agents to enter the brain and target tumor cells. In this trial, patients who received LITT followed by pembrolizumab showed substantially longer survival than those who received surgery followed by pembrolizumab.
Key Facts
- Survival improvement: Nearly 50% of patients treated with LITT plus pembrolizumab were alive at 18 months; over one-third survived beyond three years.
- Blood–brain barrier disruption: Heat from LITT transiently disrupts the BBB for several weeks, creating a therapeutic window for immunotherapy to act in the brain.
- Immune activation: Tumor debris and antigens released after LITT appear in the circulation and help activate T-cells, enhancing the systemic immune response.
- Minimally invasive: LITT is performed with MRI guidance to deliver thermal ablation precisely to tumor tissue while preserving surrounding healthy brain.
- Clinical evidence: A Phase 1/2b trial of 45 patients demonstrated that the combination is safe and associated with marked improvements in progression-free and overall survival.
Source: USC
Background: High-grade astrocytoma, including glioblastoma, is a rapidly growing brain tumor that commonly returns after surgery, leaving few effective treatment options for recurrences. Immune checkpoint inhibitors can ignite anti-tumor T-cell activity in many cancers, but they have shown limited benefit in brain tumors because the blood–brain barrier prevents immune cells and some drugs from accessing tumor tissue.
Researchers at Keck Medicine of USC designed a trial to test whether LITT can prime recurrent high-grade astrocytoma (rHGA) to respond to pembrolizumab. The rationale is that LITT destroys tumor tissue while temporarily “unsealing” the BBB, allowing tumor antigens and immune cells to interact and enabling checkpoint blockade to stimulate a durable anti-tumor response.
Trial design and main findings
The study began with a phase 1 lead-in to determine a safe dose of pembrolizumab, followed by a randomized phase 2b portion planned to compare LITT plus pembrolizumab (LITT + PEM) with non-LITT surgery plus pembrolizumab (NLS + PEM). After an interim review of accumulating data, randomization was stopped because the non-LITT arm showed limited benefit; subsequent patients were treated with LITT + PEM.
Among 39 per-protocol patients, LITT + PEM improved median overall survival to 11.8 months versus 5.2 months for NLS + PEM, and 18-month survival was 42% versus 0%. Median progression-free survival also favored LITT + PEM (4.5 versus 1.6 months). The combination was generally well tolerated with no unexpected dose-limiting toxicities reported.
Laboratory analyses indicated that LITT activates innate immune cells (non-classical monocytes) and that pembrolizumab leads to expansion and coordinated memory responses of CD8+ T cells, supporting the biological mechanism that local thermal ablation can overcome immunosuppression in the tumor microenvironment.
Procedure details
During LITT, neurosurgeons use MRI to localize the tumor and guide a small laser probe into the lesion. Controlled thermal energy destroys tumor tissue while sparing surrounding healthy brain. The transient disruption of the BBB after LITT provides a window of several weeks during which tumor-derived antigens can enter the circulation and T-cells can infiltrate the brain, allowing pembrolizumab to amplify that immune response.
Key Questions Answered
A: The study demonstrates a practical method to temporarily overcome the blood–brain barrier, enabling immunotherapy to reach and activate immune cells against brain tumors — a major obstacle in neuro-oncology.
A: This trial specifically targeted recurrent high-grade astrocytoma, one of the most aggressive brain cancers. While results are promising for this group, further studies are needed to define which patients and tumor types will benefit most.
A: LITT is minimally invasive and performed with real-time MRI monitoring to limit damage to healthy tissue. In this trial the combination with pembrolizumab was generally well tolerated, even in patients with advanced, recurrent disease.
Editorial Notes
- This article was edited by a Neuroscience News editor.
- The journal article was reviewed in full.
- Additional context was provided by staff.
About this research news
Author: Gabbi Robison ([email protected])
Source: USC
Contact: Gabbi Robison – USC
Image credit: Neuroscience News
Original Research: Open access. “Laser interstitial thermal therapy and adjuvant pembrolizumab in recurrent high-grade astrocytoma: a Phase 1/randomized Phase 2b trial” by Jian L. Campian et al., published in Nature Communications. DOI: 10.1038/s41467-026-69522-w
Abstract
Laser interstitial thermal therapy and adjuvant pembrolizumab in recurrent high-grade astrocytoma: a Phase 1/randomized Phase 2b trial
Immune checkpoint inhibitors have shown limited efficacy in recurrent high-grade astrocytoma. Laser interstitial thermal therapy (LITT) is a minimally invasive technique that may sensitize these tumors to immunotherapy by inducing tumor antigen release and transiently disrupting the blood–brain barrier.
A phase 1/randomized phase 2b trial (ClinicalTrials.gov: NCT02311582) evaluated pembrolizumab with or without LITT in patients with recurrent high-grade astrocytoma. The lead-in phase established 200 mg pembrolizumab every three weeks as the recommended dose without dose-limiting toxicities. The randomized phase compared LITT followed by pembrolizumab (LITT + PEM) to non-LITT surgery followed by pembrolizumab (NLS + PEM).
After an interim analysis, randomization stopped and subsequent participants received LITT + PEM. Among 39 per-protocol patients, LITT + PEM improved median overall survival (11.8 versus 5.2 months) and 18-month survival (42% versus 0%) compared to NLS + PEM. Median progression-free survival also favored LITT + PEM (4.5 versus 1.6 months). Treatment was well tolerated. Immunologic analyses showed activation of non-classical monocytes following LITT and expansion and coordinated memory responses of CD8+ T cells after pembrolizumab.
Overall, LITT combined with pembrolizumab appears safe and may overcome immunosuppression in recurrent high-grade astrocytoma to generate effective antitumor immunity.