Comparison of Six Cycles with Four Cycles of Chemotherapy and Atezolizumab in the First-Line Treatment of ES-SCLC; A Retrospective Multicenter Analysis

Abstract Aim IMpower133 was designed with four cycles of chemoimmunotherapy with atezolizumab, unlike many other studies permitted six-cycle induction. This study aimed to compare the efficacy and safety of a four-cycle regimen with an extended six-cycle regimen of carboplatin, etoposide, and atezolizumab in the first-line treatment of extensive-stage small cell lung cancer (ES-SCLC). Methods This retrospective multicenter study was conducted across 13 oncology centers in Turkey. A total of 181 patients with ES-SCLC who received first-line treatment with chemotherapy plus atezolizumab were analysed, and grouped into those receiving four cycles (n = 101) and six cycles (n = 80) of treatment. Results The median follow-up time was 20.9 months. The objective response rates were similar between the four- and six-cycle groups (79.2% vs. 78.8%, p = 0.940). The disease control rates were also comparable (84.2% vs. 86.3%, p = 0.940). The median progression-free survival (PFS) was 6.3 months in the four-cycle and 8.1 months in the six-cycle group (p = 0.357). The median overall survival (OS) was 16.6 months for the four-cycle and 13.6 months for the six-cycle group (p = 0.583). Intracranial progression was higher in the four-cycle group (50.0% vs. 25.5%, p = 0.007). Immune-related adverse events were similar between the groups. Conclusion XSThis is one of the largest real-world datasets comparing the efficacy and safety of four versus six cycles of induction chemoimmunotherapy. Although there were no significant improvements in PFS or OS, the six-cycle regimen was associated with a lower observed rate of intracranial progression, predominantly among patients without baseline brain metastases. Further studies are needed to identify this subject in future. Implications for Practice Extending the Carboplatin, Etoposide and Atezolizumab induction to six-cycles did not improve either PFS or OS comparing to standard four-cycle regimen. However, it may be considered in patients who do not have baseline brain metastasis, since the intracranial progression rate is significantly lower in the six-cycle group of our study and this effect of prolonged treatment was observed predominantly in patients without baseline brain metastasis. The immune-related adverse events were similar across the six-cycle and the four-cycle groups.