P66.01 Characterize the Heterogeneity of the Immunophenotype in Different Neuroendocrine (NE) Subtypes of Small-Cell Lung Cancer (SCLC)

Abstract

SCLC is a typical neuroendocrine carcinoma, however, a variant subtype of SCLC with low expression of NE markers and a variant morphology has been reported mainly based on cell lines and xenograft models. The difference of the tumor immune microenviroment (TIME) and other clinicopathological characteristics between the two subtypes in human specimens remain to be investigated. Forty-eight resected Formalin-Fixed and Paraffin-Embedded (FFPE) SCLC tissues were collected for mRNA detection using Nanostring technology. Patients were assigned into NE-high and NE-low group according to NE gene signature score, and the expression level of immune-related genes and abundance of immunocytes estimated by CIBERSORT was compared between the two groups. Nanostring digital spatial profiling (DSP) was performed in 6 NE score paired tumors to dissect the heterogeneity of spatial distribution of immune cells and immunotherapeutic drug targets between the two subtypes. Kaplan-meier method and COX regression model was used to compare the survival of the two subtypes and identify the independent prognostic factors and potential immunotherapeutic targets respectively. Forty-eight patients were assigned into the NE-high and NE-low group respectively based on NE score. NE-low group had earlier clinical stages (P=0.030), higher positive rates of lymph nodes (P=0.017) and higher frequency of variant morphology (P=0.047) than that of NE-high group. Compared with NE-high tumors, most of the detected immune-related genes were up-regulated in NE-low tumors. CIBERSORT results indicated NE-high subtypes had a higher relative proportion of Treg cells and M2 macrophages. However, higher absolute abundance of activated mast cells, CD8+ T cells and M1 macrophages enriched in NE-low TME. DSP results showed NE-high tumors were lack of dendritic cells and macrophages in peritumor area and normal tissue compartments and also lack of effector T cells in tumor center and surrounding area. However, a set of targetable negative immune checkpoints were up-regulated in NE-low TME. The prognosis was better for NE-low patients with 5-year DFS% 75% vs.38.6% (hazard ratio [HR] 0.35, 95% confidence interval [CI] 0.08-1.46; P=0.130) and 5-year OS% 87.5% vs.53.9% (HR 0.19, 95% CI 0.03-1.43; P=0.073). SCLC patients exhibited heterogeneous NE gene expression profile, implicating two entities with distinct TIME and prognosis. Compared with NE-high subtypes, patients with NE-low tumors had higher expression of immune-related genes, showing T cell-inflamed immunophenotypes, which might be one of causes for longer survival and suggested a higher propensity to benefit from immunotherapy.