IMpower133
In extensive-stage SCLC, does atezolizumab added to carboplatin–etoposide improve survival?
One underlying study; aliases and follow-up reports consolidated. Primary discipline: Medical.
403 patients with previously untreated extensive-stage small-cell lung cancer.
Previously untreated extensive-stage SCLC fit for carboplatin–etoposide.
403 randomised/evaluable as reported.
Atezolizumab 1,200 mg plus carboplatin AUC 5 and etoposide 100 mg/m² days 1–3 for four 21-day cycles, then atezolizumab maintenance.
Placebo plus the same chemotherapy, followed by placebo maintenance.
Endpoints and results
Co-primary endpoints OS and investigator-assessed PFS.
- Median OS 12.3 vs 10.3 months; HR 0.70 (95% CI 0.54–0.91; p=0.007).
- Median PFS 5.2 vs 4.3 months; HR 0.77 (95% CI 0.62–0.96; p=0.02).
- Grade 3–4 treatment-related AEs 57.1% vs 56.1%; grade 5 treatment-related AEs 1.5% each.
Absolute Effect and outcome visualisation
Median OS
months (median, not fixed-time rate) · Primary analysis. Bars compare reported medians only and are not fixed-time survival probabilities.
Interpretation: No fixed-time OS rates included here; NNT not calculated. Never derive NNT from median OS difference or HR.
Toxicity, discontinuation and quality of life
Trial-specific harms: Myelosuppression and infection from chemotherapy; immune-mediated toxicity from atezolizumab. Overall grade 3–4 treatment-related toxicity was similar.
Treatment burden/discontinuation: Four cycles of combination therapy followed by maintenance; exact discontinuation rates require the primary safety tables.
Quality of life: No numerical comparative QoL effect asserted.
Subgroups, maturity and limitations
Subgroups: Benefit reported across major clinical subgroups; no biomarker selection required.
Maturity: Long-term follow-up supports durable OS benefit; primary report remains foundational.
Limitations: Extensive-stage only; do not conflate with limited-stage consolidation trials.
IMpower133 established first-line chemoimmunotherapy for extensive-stage SCLC with modest median OS gain and similar overall severe treatment-related AE rates.
Current-practice context must be checked against regional guidelines, patient fitness, biomarkers, alternatives and regulatory status before clinical application. Clinical freshness review and browser-rendered QA remain pending.
Primary sources and registry
Registry: NCT02763579
The Absolute Effect · Updated 26 October 2026 · Never derive NNT from median survival.