The phase 2 TREASURE clinical trial (NCT04462276) demonstrated that adding consolidative thoracic radiotherapy to atezolizumab maintenance therapy fails to improve survival in patients with extensive-stage small cell lung cancer (ES-SCLC). According to findings published in JAMA Oncology, the combination increased the frequency of fatal adverse events, prompting investigators to halt the study early due to safety concerns.
Survival Outcomes and Treatment Efficacy
The TREASURE trial, which enrolled patients across 20 sites in Germany and Austria, found no clinical benefit to the experimental combination. Patients receiving atezolizumab maintenance combined with 30 Gy of thoracic radiotherapy (arm A) saw a median overall survival (OS) of 6.7 months, compared to 13.4 months for those receiving atezolizumab maintenance alone (arm B). The hazard ratio (HR) for OS was 1.55 (95% CI, 0.90-2.69; P = .34).
The study was designed to enroll 104 patients to detect a 20% improvement in 12-month survival but stopped early at 68 participants. Because of this reduced sample size, researchers categorized the findings as descriptive rather than definitive. Median progression-free survival (PFS) was nearly identical between the two groups—2.4 months for the combination arm versus 2.6 months for the monotherapy arm—suggesting that the radiotherapy provided no meaningful additional tumor control.
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The researchers noted that the survival disparity between the two study arms was likely driven by treatment-related toxicity rather than tumor progression, given that PFS remained stagnant despite the added radiation.
Safety Concerns and Lymphocyte Depletion
The safety data from the TREASURE trial revealed a marked increase in serious adverse events (AEs). According to the study report, 61.3% of patients in the combination arm experienced serious AEs, compared to just 18.2% in the atezolizumab-only arm (P < .001). More critically, 19.4% of patients in the combination arm suffered fatal AEs, compared to 3.0% in the control arm (P = .04).
Investigators identified a physiological mechanism behind these outcomes: patients undergoing radiotherapy experienced pronounced and persistent depletion of lymphocytes. This specific reduction in immune cells, which was not observed in leukocyte or neutrophil counts, appeared to correlate with a higher incidence of infections and respiratory disorders, such as pneumonitis. Additionally, lower baseline diffusing capacity of the lungs for carbon monoxide was identified as a potential predictor for fatal AEs in those receiving radiation.
Contextualizing Results with Prior Trials
These findings align with data from recent non–small cell lung cancer (NSCLC) studies, specifically the PACIFIC-2 (NCT03519971) and CheckMate 73L (NCT04026412) trials. Both studies reported higher rates of fatal infections and toxic effects when concurrent thoracic chemoradiotherapy was paired with immunotherapy. The consistency across these trials suggests a broad challenge in integrating radiotherapy with checkpoint inhibitors in lung cancer treatments.
Clinicians should consider limiting radiation dose exposure to highly perfused organs at risk and carefully adjust the timing of radiotherapy relative to immunotherapy cycles, as recommended by the TREASURE investigators.
Future Directions for ES-SCLC Research
The authors of the TREASURE trial explicitly stated that consolidative thoracic radiotherapy cannot be recommended for unselected patients with ES-SCLC outside of clinical trials. Moving forward, the research community is looking toward biomarker analyses to determine if specific patient subgroups might tolerate this treatment approach without excess risk.
Future study designs are expected to incorporate prospectively defined safety stopping rules to protect patient welfare. Researchers are also investigating whether refining the radiation delivery protocols—specifically focusing on avoiding sensitive organs—could mitigate the severe immune-related toxicities observed in recent trials.
Frequently Asked Questions
Why was the TREASURE trial stopped early?
The trial was stopped early because of significant safety concerns, specifically a higher-than-expected rate of serious and fatal adverse events in the group receiving both atezolizumab and thoracic radiotherapy.
Did the addition of radiotherapy improve survival?
No. The trial found that the addition of radiotherapy did not improve overall survival or progression-free survival compared to atezolizumab maintenance alone.
What caused the increased toxicity in the combination group?
Researchers observed a persistent depletion of lymphocytes in patients who received radiotherapy, which they believe facilitated higher rates of serious infections and respiratory complications.
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