Abstract 7567: In-depth mass cytometry analysis reveals different immune cell composition of unique molecular subtypes in extensive stage small-cell lung cancer

Abstract Background: A novel molecular subtype classification was fashionable for small cell lung cancer (SCLC). However, the distribution of SCLC molecular subtype classification in Chinese patients were unknown, especially extensive stage (ES) -SCLC. It should validate and define their associated microenvironments across subtypes in ES-SCLC. Method: We used immunohistochemical (IHC) to evaluate SCLC markers of the subtypes including ASCL1, NEUROD1, POU2F3, SCLC-A/N/P in 135 ES-SCLC tumors. Peripheral blood of 24 ES-SCLC patients was test by mass cytometry using time-of-flight (CyTOF) to evaluate the differences in immune subsets regard to the subtype tumor microenvironment (TME). Validation was performed using flow cytometry and multiplex IF. Results: ASCL1, NEUROD1, POU2F3, and Inflamed were account for 60. 7%, 28. 9%, 7. 4%, and 18. 5% of SCLC tumors, respectively. Significant intratumoral heterogeneity was observed with 15. 6% of the tumors being both positive for SCLC-A and -N subtype markers, respectively. The SCLC-I type possessed more CD8+ T-cells infiltration and had higher frequency an ‘inflamed’ immunophenotyped. CyTOF data showed greater CD161+CD127+CD8+T cells proportion in SCLC-I than SCLC-N subtypes before and after anti-immunotherapy. Furthermore, we validated that lung tissue of SCLC-I were infiltrated more CD161+CD127+CD8+T cells compared to SCLC-N subpopulation (P=0. 0281). Flow cytometry further showed the stronger immune activation of CD161+CD127+CD8+T cells in SCLC-I types induced higher expression of GZMB and GNLY and lower-expression of T-cell exhaustion markers PD-1, TIGIT and LAG3 in comparison with SCLC-N types. We further confirmed that the high level of CD161+CD127+CD8+T associated with a favorable treatment response and prolonged overall survival. Conclusion: The present study validated the molecular subtypes in ES-SCLC patients. Furthermore, SCLC-I subtype has longer PFS and OS than SCLC-A, -N and -P patients. Our research not only provides an insight into the immune landscape of ES-SCLC but also sheds light on a special subset of CD161+CD127+CD8+T cells with prognostic and therapeutic significance. Citation Format: Yuekang Li, Jingjing Qu, Binggen Wu, Qian Shen, Wenjia Sun, Lijun Chen, Bo Wang, Lixiong Ying, Jianya Zhou, Jianying Zhou. In-depth mass cytometry analysis reveals different immune cell composition of unique molecular subtypes in extensive stage small-cell lung cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 7567.