IMpower133: Atezolizumab in Combination With Chemotherapy in Previously Untreated, Extensive-Stage Small Cell Lung Cancer

The phase III IMpower133 study recently met its coprimary endpoints of overall survival (OS) and progression-free survival (PFS) at its first interim analysis. The study demonstrated that first-line treatment with the combination of atezolizumab (Tecentriq) plus chemotherapy (carboplatin and etoposide) helped people with extensive-stage small cell lung cancer live significantly longer compared to chemotherapy alone. The atezolizumab-based combination improved progression-free survival (PFS) compared to chemotherapy alone. Safety for the atezolizumab and chemotherapy combination appeared consistent with the known safety profile of the individual medicines, and no new safety signals were identified with the combination. These data will be presented at an upcoming medical meeting.

“These are the first positive phase III survival results for any immunotherapy-based combination in the initial treatment of extensive-stage small cell lung cancer, a particularly difficult-to-treat type of disease,” said Sandra Horning, MD, Chief Medical Officer and Head of Global Product Development, Genentech. “The clinically meaningful results from the IMpower133 study add to the growing body of evidence demonstrating that atezolizumab-based combinations may be an effective treatment for different types of advanced lung cancer. We look forward to working with health authorities globally to bring this potential treatment option to people with this type of disease as soon as possible.” 

About the IMpower133 study

IMpower133 is a phase III, multicenter, double-blinded, randomized placebo-controlled study evaluating the efficacy and safety of atezolizumab in combination with carboplatin and etoposide vs chemotherapy (carboplatin plus etoposide) alone in chemotherapy-naive patients with extensive-stage small cell lung cancer. The study enrolled 403 people who were randomized equally (1:1) to receive:

  • Atezolizumab in combination with carboplatin and etoposide (arm A), or
  • Placebo in combination with carboplatin and etoposide (arm B, control arm)

During the treatment-induction phase, people received treatment on 21-day cycles for four cycles, followed by maintenance with atezolizumab or placebo until progressive disease as assessed by the investigator using Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST v1.1). Treatment could be continued until persistent radiographic progressive disease or symptomatic deterioration was observed.

 The coprimary endpoints were:

  • PFS as determined by the investigator using RECIST v1.1 in the intention-to-treat (ITT) population
  • OS in the ITT population

IMpower133 met its OS and PFS co-primary endpoints as per the study protocol.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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