IMpower 133: Primary PFS, OS and Safety in a PH1/3 Study of 1L Atezolizumab + Carboplatin + Etoposide in Extensive-Stage SCLC
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First-line (1L) standard-of-care treatment for extensive-stage small cell lung cancer (ES-SCLC) is platinum (carboplatin or cisplatin) with etoposide. Despite high initial response rates, there has been limited progress in the last two decades and outcomes remain poor with a median overall survival (OS) of ~10 months. IMpower133 (NCT02763579), a global Phase 1/3, double-blind, randomized, placebo-controlled trial evaluated efficacy and safety of adding atezolizumab, a humanized monoclonal anti–PD-L1 antibody, or placebo to 1L carboplatin and etoposide in ES-SCLC.

Patients with measurable (RECIST v1.1) ES-SCLC, ECOG performance status 0 or 1, who had not received prior systemic treatment for ES-SCLC were enrolled. PD-L1 immunohistochemical testing was not required. Patients were randomized 1:1 to receive four 21-day cycles of carboplatin (AUC 5 mg/mL/min IV, Day 1) plus etoposide (100 mg/m2 IV, Days 1-3) with either atezolizumab (1200 mg IV, Day 1) or placebo, followed by maintenance therapy with atezolizumab or placebo until intolerable toxicity or progressive disease per RECIST v1.1. Patients meeting predefined criteria could receive treatment beyond progression. Co-primary endpoints were OS and investigator-assessed progression-free survival (PFS). Adverse events (AEs) were graded per NCI-CTCAE v4.0. Blood-based tumor mutation burden (bTMB) was assessed using prespecified cutoffs of ≥16 vs. <16 and ≥10 vs. <10 mutations/Mb.

In total, 201 patients were randomized to the atezolizumab group, and 202 to the placebo group. Median follow-up was 13.9 months. Median OS was 12.3 months in the atezolizumab group and 10.3 months in the placebo group (hazard ratio [HR] 0.70 [95% confidence interval (CI): 0.54, 0.91; P=0.0069]). Median PFS was 5.2 months and 4.3 months, respectively (HR 0.77 [95% CI: 0.62, 0.96; P=0.017]). OS and PFS benefits were consistent across key patient subgroups. Investigator-assessed confirmed objective response rates were 60.2% and 64.4% in the atezolizumab and placebo groups, respectively; median duration of response, 4.2 and 3.9 months. Exploratory analyses showed OS survival benefits in subgroups above and below prespecified bTMB cutoffs. Grade 3-4 treatment-related AEs were reported in 56.6% vs. 56.1% patients in atezolizumab vs. placebo groups, respectively; serious treatment-related AEs occurred in 22.7% and 18.9% patients, respectively.

Addition of atezolizumab to carboplatin and etoposide provided a significant improvement in OS and PFS in 1L ES-SCLC in an all-comer patient population. No unexpected safety signals were identified. Atezolizumab plus carboplatin and etoposide may represent a new standard regimen for patients with untreated ES-SCLC.
All Author(s) ListStephen V Liu, Aaron S. Mansfield, Aleksandra Szczesna, Libor Havel, Maciej Krzakowski, Maximilian Johannes Hochmair, Florian Huemer, Gyorgy Losonczy, Melissa L. Johnson, Makoto Nishio, Martin Reck, Tony S. Mok, Sivuonthanh Lam, David S. Shames, Juan Liu, Beiying Ding, Fairooz Kabbinavar, Wei Lin, Alan Sandler, Leora Horn
Name of ConferenceWCLC 2018, 19th World Conference on Lung Cancer
Start Date of Conference23/09/2018
End Date of Conference26/09/2018
Place of ConferenceToronto
Country/Region of ConferenceCanada
Proceedings TitleJournal of Thoracic Oncology
Series TitlePlenary Session
Number in SeriesAbst PL02.07
Volume Number13
Issue NumberSuppl 10
PagesS185 - S186
LanguagesEnglish-United Kingdom
KeywordsAtezolizumab, Carboplatin, Etoposide

Last updated on 2020-12-07 at 00:55