Why This Study Matters
Atezolizumab plus carboplatin-etoposide is the standard first-line treatment for extensive-stage small cell lung cancer (ES-SCLC), established by the overall survival benefit seen in the IMpower133 trial. Whether adding consolidative thoracic radiotherapy (TRT) to immunotherapy maintenance can further improve outcomes — as radiotherapy has done in non-small cell lung cancer — remained poorly defined for ES-SCLC prior to this trial.
The TREASURE trial set out to test whether adding consolidative TRT to atezolizumab maintenance therapy could improve outcomes for patients with ES-SCLC, building on the modest survival gains seen with radiotherapy in the pre-immunotherapy era (CREST trial) and on encouraging results combining radiotherapy with immunotherapy in non-small cell lung cancer.
Study Design
TREASURE (AIO-TRK-0320) was a multicenter, open-label, randomized (1:1) phase 2 clinical trial conducted at 20 sites in Germany and Austria. The primary endpoint was overall survival (OS), measured from randomization to death from any cause. Patients in Arm A received atezolizumab maintenance plus consolidative thoracic radiotherapy (TRT, 30 Gy in 10 fractions), while Arm B received atezolizumab maintenance alone.
Patient Population
Eligible patients had ES-SCLC with at least stable disease after induction chemoimmunotherapy (carboplatin-etoposide-atezolizumab). Of 96 patients screened, 68 (71%) were randomized 1:1 to the two maintenance strategies, with 34 patients in each arm.
Primary Endpoint: Overall Survival
Median overall survival was numerically shorter in Arm A (atezolizumab + TRT) than Arm B (atezolizumab alone). Notably, the OS curves crossed at approximately 24 months, with 2-year rates numerically favoring Arm A — an observation the authors describe as requiring cautious interpretation given the small number of patients remaining at risk at that timepoint.
Progression-free survival was essentially identical between arms (2.4 vs 2.6 months; HR, 0.92; P=.85). The authors note this dissociation between PFS and OS is clinically informative: because PFS was unaffected, the OS detriment in Arm A points to treatment-related toxicity — rather than accelerated tumor progression — as the primary driver of the survival difference.
Subgroup Analyses
Safety Profile
Toxicity was substantially higher with the addition of TRT. Any toxic effect occurred in 96.8% of Arm A vs 75.8% of Arm B (P=.02); serious adverse events in 61.3% vs 18.2% (P<.001); treatment-related AEs in 71.0% vs 30.3% (P=.001); and fatal AEs in 19.4% (6/34) vs 3.0% (1/34) (P=.04). Predominant Arm A adverse-event categories were infections (urinary, pulmonary), gastrointestinal effects (dysphagia, esophagitis), respiratory events (notably pneumonitis), fever, and skin disorders. Arm A also showed persistent radiation-induced lymphocyte depletion.
| Outcome | Arm A (Atezolizumab + TRT), n=34 | Arm B (Atezolizumab Only), n=34 | P value |
|---|---|---|---|
| Any toxic effect | 96.8% (30) | 75.8% (25) | .02 |
| Serious adverse events (SAEs) | 61.3% (19) | 18.2% (6) | <.001 |
| Treatment-related AEs | 71.0% | 30.3% | .001 |
| Treatment-related SAEs | 29.0% | 6.1% | .01 |
| Fatal adverse events | 19.4% (6) | 3.0% (1) | .04 |
| Absolute Lymphocyte Count <0.001/µL | Arm A | Arm B | P value |
|---|---|---|---|
| Baseline | 25.8% (8/31) | 15.2% (5/33) | .31 |
| Cycle 1 | 25.9% (7/27) | 20.0% (5/25) | .61 |
| Cycle 2 | 91.7% (22/24) | 13.6% (3/22) | <.001 |
| Cycle 3 | 77.8% (14/18) | 26.7% (4/15) | .004 |
| Cycle 4 | 69.2% (9/13) | 8.3% (1/12) | .002 |
Causal attribution of the fatal events was contested: investigators judged 4 of 6 fatalities in Arm A unrelated to treatment, while the trial’s Safety Monitoring Committee classified 3 of these as possibly or probably treatment-related.
Interpretation and Broader Context
These findings argue against routine addition of consolidative thoracic radiotherapy to atezolizumab maintenance in unselected patients with ES-SCLC: toxicity, including fatal events, increased without a survival or progression-free survival benefit. The trial was halted early by the Safety Monitoring Committee due to this unfavorable risk-benefit balance, and the authors state that consolidative TRT in this setting cannot currently be recommended outside clinical trials.
This finding is consistent with the randomized PACIFIC-2 and CheckMate-73L trials in non-small cell lung cancer, both of which observed more fatal infections and toxic effects when thoracic chemoradiotherapy was combined simultaneously with immunotherapy — suggesting a class-level interaction between concurrent thoracic radiotherapy and immunotherapy that spans tumor types.
TREASURE is a negative phase 2 trial: adding consolidative thoracic radiotherapy to atezolizumab maintenance in unselected ES-SCLC increased serious and fatal toxicity without improving overall or progression-free survival, and was stopped early for an unfavorable risk-benefit balance. Future studies should explore mitigation strategies — reduced radiation dose to organs at risk, altered radiotherapy timing relative to immunotherapy cycles, and prospectively defined safety stopping rules — alongside biomarker analyses to identify subpopulations at particular risk or benefit.