Background
Phase 3, open-label, randomized; 96 sites, 13 countries. Treatment-naive ES-SCLC without progression after 4 cycles induction (atezolizumab + carboplatin + etoposide). 483 randomized 1:1 into maintenance. Brain metastases excluded at induction.
Results
Interventions and follow up: Arm A: lurbinectedin 3.2 mg/m² IV q3wk (+ G-CSF prophylaxis) + atezolizumab 1200 mg IV q3wk (n=242).
Arm B: atezolizumab 1200 mg IV q3wk alone (n=241).
Primary endpoint: co-primary IRF-PFS and OS, from maintenance randomization.
mFollow up: ~15 mo; data cutoff Jul 29, 2024.
Results: IRF-PFS: 5.4 vs 2.1 mo, stratified HR 0.54, 95% CI 0.43–0.67, P<.001.
OS: 13.2 vs 10.6 mo, stratified HR 0.73, 95% CI 0.57–0.95, P=.017.
Both co-primary endpoints met (first global phase 3 maintenance OS win in ES-SCLC).
Arm B: atezolizumab 1200 mg IV q3wk alone (n=241).
Primary endpoint: co-primary IRF-PFS and OS, from maintenance randomization.
mFollow up: ~15 mo; data cutoff Jul 29, 2024.
Results: IRF-PFS: 5.4 vs 2.1 mo, stratified HR 0.54, 95% CI 0.43–0.67, P<.001.
OS: 13.2 vs 10.6 mo, stratified HR 0.73, 95% CI 0.57–0.95, P=.017.
Both co-primary endpoints met (first global phase 3 maintenance OS win in ES-SCLC).
Adverse events
Grade 3-4: 38% (lurbi+atezo) vs 22% (atezo).
Grade 3-4, lurbi+atezo: anaemia 8%, decreased neutrophils 7%, decreased platelets 7%.
Grade 5: 5% vs 3%.
Pattern: excess myelosuppression with the combination.
Grade 3-4, lurbi+atezo: anaemia 8%, decreased neutrophils 7%, decreased platelets 7%.
Grade 5: 5% vs 3%.
Pattern: excess myelosuppression with the combination.
Conclusions
Lurbinectedin + atezolizumab maintenance significantly prolonged both PFS and OS vs atezolizumab alone in ES-SCLC responders, at the cost of more, mostly hematologic, toxicity. First positive maintenance regimen to extend OS over IO maintenance; supported FDA approval.
Key Limitations
Open-label design (PFS bias risk despite independent review). Only post-induction non-progressors randomized, so benefit applies to a selected fitter subgroup; baseline brain metastases excluded. Short follow-up; absolute OS gain modest (~2.6 mo). Added myelosuppression and routine G-CSF affect tolerability and resource use.
Clinical Context
Builds on the IMpower133 chemoimmunotherapy backbone, moving lurbinectedin from relapse into first-line maintenance. FDA approved this maintenance regimen in ES-SCLC; ESMO/ASCO frameworks endorse maintenance IO after induction, and IMforte adds the first OS-positive maintenance option. Practical use hinges on post-induction responder selection, good performance status, G-CSF support, and cytopenia monitoring; the modest absolute gain invites shared decision-making.