Abstract 6614: Small cell lung cancer (SCLC) at recurrence has a “colder” tumor microenvironment than primary SCLC according to gene expression profiling

Abstract Recent studies have described the tumor microenvironment and the key transcription factors in untreated small cell lung cancer (SCLC), but less is known about the salient features in recurrent SCLC (rSCLC). This information could provide valuable insight about the effectiveness of second and later line therapies. In this study, we compared transcriptome profiles (by RNA-seq) of rSCLC against untreated primaries (pSCLC). rSCLC samples (n=23) were obtained from frozen biopsies in patients enrolled in our MC1923 (NCT04607954) phase 2 clinical trial whose disease progressed after chemoimmunotherapy. The pSCLC group (n=73) included publicly available data from fresh frozen primary tumors after surgical resections. Normalized expression data were used in immune deconvolution and gene set enrichment analysis (GSEA) in molecular signature database. Additional GSEA included gene sets describing ASCL1 (A), NEUROD1 (N), ASCL1 and NEUROD1 (AN), and POU2F3 (P) transcription factor activities which are used for subtyping of SCLC. Immune deconvolutions by multiple software algorithms suggested depletion of immune infiltrates in rSCLC compared with pSCLC including dendritic cells, B cells, CD8+ T cells, and M1 macrophages. Furthermore, we found decreased chemotaxis and increased apoptosis of dendritic cells, reduced TNF signaling, and reduced lymphocyte co-stimulation in rSCLC by GSEA. Additionally, in comparisons with pSCLC, rSCLC tumors had significantly lower enrichment scores for POU2F3 activity, representing the SCLC-P subtype (p < 0.007). Importantly, the SCLC-P was recently reported to be more immune inflamed than the other A, N, and AN subtypes. Altogether, our analyses provide strong evidence that the tumor microenvironment of rSCLC is significantly more immunosuppressed and with reduced immune cell infiltrates compared to pSCLC. Developing therapeutic strategies aimed at “warming” the tumor microenvironment and enhancing anti-tumor immune activity in ongoing multimodal therapies of recurrent SCLC will likely provide significant benefits to patients. Citation Format: Farhad Kosari, Mohamed Ali, Sarah H. Johnson, Alex Adjei, Julian R. Molina, Aaron S. Mansfield, Anastasios Dimou, Kaushal Parikh, Mohamed Shanshal, Katherine E. Smith, Ailsa G. Luce, Anna J. Schwecke, Janet Lensing, Ying-Chun Lo, John C. Cheville, George Vasmatzis, Konstantinos Leventakos. Small cell lung cancer (SCLC) at recurrence has a “colder” tumor microenvironment than primary SCLC according to gene expression profiling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6614.