164P Immune cells distribution and spatial relationship within microenvironment as predictive biomarkers of benefit in extended stage small cell lung cancer patients receiving atezolizumab plus carboplatin and etoposide as first-line treatment

Atezolizumab plus carboplatin-etoposide (ACE) represents the new first-line (1L) standard of care for extended stage (ES) Small Cell Lung Cancer (SCLC) patients (pts). This is a single-center retrospective-prospective translational study aiming at investigating correlation immune cell distribution and their spatial metrics in tumor samples ES SCLC pts receiving ACE as 1L treatment, with response rate (RR), progression-free survival (PFS), time to treatment failure (TTF) overall (OS). A 9-color multiplex immunofluorescence panel including primary antibodies (Abs) against CD68, CD163, CD8, FoxP3, CD4, CD20 HLA-I mix Abs markers has been performed. Preliminary data on first 39 are reported. After median follow-up 7.2 months (mos), estimated PFS, TTF OS were 5.4 (95% CI 4.5–6.3), 5.8 3.5–8.1), 7.8 mos 1.9–13.7), respectively. Lower CD163+ M2-polarized macrophages density ratio CD8+ cells total tumoral areas favorably associated RR, (p < 0.05). High intra-tumoral CD4+FoxP3+ correlated better PFS = 0.004), 0.011) 0.026). CD20+ B lymphocyte infiltration longer OS. positive role interaction 0.038), (intra-tumoral, p 0.036) 0.032) observed. percentage (%) stromal close low % 0.045) TTF(p 0.034). CD4+ closed area 0.025) stroma 0.002), intra peri-tumoral between 0.020) 0.008), 0.012), We identified that populations cell-to-cell ES-SCLC significantly outcome, highlighting importance microenvironment survival.