Five-year survival in patients with extensive-stage small cell lung cancer treated with atezolizumab in the Phase III IMpower133 study and the Phase III IMbrella a extension study

Abstract

Objectives IMbrella A is a Phase III extension study that allowed rollover from Roche/Genentech–sponsored atezolizumab trials, including IMpower133, a Phase I/III trial of first-line atezolizumab or placebo plus carboplatin/etoposide in extensive-stage small cell lung cancer. We report outcomes from an exploratory analysis of IMpower133 with extended time-to-event data for patients who rolled over to IMbrella A. Materials and Methods IMpower133 patients could roll over to IMbrella A to receive atezolizumab 1200 mg intravenously every 3 weeks if they continued to receive atezolizumab at IMpower133 closure or were in survival follow-up after atezolizumab discontinuation. Overall survival and safety were assessed; only serious adverse events and AEs of special interest were collected in IMbrella A. Results Eighteen of 26 eligible patients rolled over to IMbrella A. At clinical cutoff (March 16, 2023), median follow-up in the atezolizumab plus carboplatin/etoposide arm (IMpower133 and IMbrella A) was 59.4 months. The 3-, 4-, and 5-year overall survival (95 % CI) estimates were 16 % (11 %–21 %), 13 % (8 %–18 %), and 12 % (7 %–17 %), respectively. In IMbrella A, serious adverse events occurred in three patients (16.7 %), and one adverse event of special interest was reported (grade 2 hypothyroidism). Conclusion This long-term analysis of patients from IMbrella A previously enrolled in IMpower133 provides the first report of 5-year overall survival outcomes in patients with extensive-stage small cell lung cancer treated with first-line cancer immunotherapy and chemotherapy. While limited by small patient numbers and lack of long-term data for the IMpower133 control arm, exploratory overall survival analyses in patients treated with atezolizumab plus carboplatin/etoposide compared favorably with historical data with chemotherapy alone. NCT03148418.