First-line sintilimab combined with platinum-based chemotherapy in extensive stage small cell lung cancer: A phase II study and post-hoc biomarker analysis.

e20127 Background: Immune checkpoint inhibitors (ICIs) combined with etoposide and platinum-based chemotherapy improves prognosis of patients with extensive-stage small-cell lung cancer (ES-SCLC). However, nearly 40% of patients do not benefit from Immunochemotherapy. Herein, this phase II study of first-line immunochemotherapy was conducted aiming to investigate potential biomarkers associated with therapeutic efficacy. Methods: A multi-center, single-arm, prospective phase II trial (ChiCTR2000038354) was designed and conducted to evaluate the efficacy and safety of sintilimab combined with platinum-based chemotherapy in patients with ES-SCLC who had not previously received treatment. The primary endpoint of this study is progression-free survival (PFS), with patients being defined as disease progression according to RECIST 1.1. Pre-treatment FFPE samples were analyzed using whole exome sequencing (WES) and whole transcriptome sequencing (WTS) to investigate biomarkers. Results: A total of 44 patients were included in the study, with a median follow-up of 10 months and a median PFS of 7.57 months. 8 patients with a PFS greater than 6 months were defined as the responder group (R group) and 5 patients with a PFS less than 6 months belonged to the non-responder group (NR group). WES and WTS were performed on the pre-treatment samples of these 13 patients. WES results revealed mutation frequencies of TP53 (69%), RB1 (31%) and FAT1 (31%) aligning with prior research. Significantly, ZFHX4 mutations correlated with R group (p = 0.05). Genomic instability, as defined by Homologous Recombination Deficiency (HRD) scores, displayed higher scores in NR group than in R group (p = 0.023), which suggests potential benefits of PARP inhibition in the NR group. WTS data revealed that higher M2/M1 macrophage ratio (p = 0.028) in NR group. Additionally, the NR group demonstrated significant VEGFA overexpression. Besides, NOTCH-signaling (p = 0.034), KRAS-signaling-DN (p<0.001), Angiogenesis (p<0.001) and EMT (p<0.001) pathway were also enriched in NR group. Conversely, M1 macrophages (p = 0.079), CD4+T cells (p = 0.093), Mast cells (p = 0.045), NK cells (p = 0.045) and neutrophils (p = 0.06) was higher in R group. Conclusions: This study highlights genomic instability as well as activation of cancer hallmarks such as angiogenesis, EMT may result the resistance to immunotherapy in ES-SCLC patients. These findings may shed light on combinational strategy overcoming therapeutic resistance. Clinical trial information: ChiCTR2000038354.