A new multicenter clinical trial has revealed complex findings regarding the use of pembrolizumab immunotherapy in patients with recurrent glioblastoma. The study, which expanded upon previous research, demonstrated significant molecular changes in treated tumors while yielding mixed clinical outcomes.
The expansion cohort enrolled 25 patients across four institutions between June 2020 and August 2021. Participants received a single dose of pembrolizumab approximately two weeks before tumor resection, followed by regular pembrolizumab treatment every three weeks until disease progression or unacceptable toxicity.
Key Molecular Findings
The trial met its primary pharmacodynamic endpoint, showing that pembrolizumab treatment significantly decreased cell cycle and cancer proliferation gene signatures in treated tumor tissue. The median cell cycle-related enrichment score dropped to -0.2996 in pembrolizumab-treated tumors, compared to 0.5172 in untreated tissue (p=0.009).
Analysis revealed that patients whose tumors showed both high interferon signatures and low cell cycle signatures demonstrated the best survival outcomes, with a median survival of 420 days (13.8 months). This favorable molecular profile was exclusively observed in patients who received neoadjuvant pembrolizumab treatment.
Clinical Outcomes and Survival
The expansion cohort showed more modest survival outcomes compared to the initial study:
- Median overall survival: 204 days (6.8 months) in the expansion cohort vs. 417 days (13.7 months) in the initial neoadjuvant cohort
- Progression-free survival: 75 days (2.5 months) in the expansion cohort vs. 99.5 days (3.3 months) in the initial cohort
- Six-month progression-free survival rate was 0% in the expansion cohort, compared to 33.3% in the initial neoadjuvant cohort
Safety Profile
The treatment demonstrated an acceptable safety profile, with six grade 3 or higher adverse events reported, including:
- Cerebral edema (2 cases)
- Headache
- Fatigue
- Adrenal insufficiency
- Hyperthyroidism
Biomarker Insights
Detailed analysis identified four distinct patient subgroups based on cell cycle and interferon-gamma gene signatures. The study found that STAT3 and TNF-α-related gene signatures were elevated in patients with poorer outcomes, suggesting potential resistance mechanisms to immunotherapy.
The findings underscore the importance of molecular profiling in predicting treatment response and highlight the complex relationship between immune activation and tumor control in glioblastoma. While the treatment showed promising biological effects, the variable clinical outcomes suggest the need for further investigation into resistance mechanisms and potential combination strategies.
