Abstract 4546: Comprehensive analysis using transcriptional factor based molecular subtypes and correlation to clinical outcomes in small-cell lung cancer
Authors: Park Sehhoon , Hong Tae Hee , Hwang Soohyun , Jung Hyun-Ae , Sun Jong-Mu , Ahn Jin Seok , Ahn Myung-Ju , Cho Jong Ho , Choi Yong Soo , Kim Jhingook , Shim Young Mog , Kim Hong Kwan , Choi Yoon-La , Lee Se-hoon , Park Keunchil 
Published: April 2023

Abstract
Background: Several studies have reported the predictive and prognostic value of novel transcriptional factor-based molecular subtypes in small-cell lung cancer (SCLC). We conducted an in-depth analysis using multi-omics data to elucidate the underlying characteristics that lead to differences in clinical outcomes between subtypes.
Patients and Methods: Immunohistochemistry (IHC, n=252), target exome sequencing (n=422), and whole transcriptome sequencing (WTS, n=189) data generated from 427 patients with SCLC patients were comprehensively analyzed. The differences in the mutation profile, gene expression profile were analyzed according to the IHC-based molecular subtype. Clinical implication was evaluated based on treatment outcomes of individual patients.
Results: IHC based molecular subtyping revealed a high incidence of ASCL1 subtype (SCLC-A, 56.3%) followed by ASCL1/NEUROD1 co-expressed (SCLC-trans, 17.9%), NEUROD1 (SCLC-N, 12.3%), POU2F3 (SCLC-P, 9.1%), triple-negative (SCLC-TN, 4.4%) subtypes showing high concordance with WTS-based subtyping. We delineated the SCLC-trans subtype resembling SCLC-A rather than SCLC-N in terms of both gene expression profiles and clinical outcomes. SCLC-TN type was defined as non-significant expression of A, N, P. Favorable overall survival (OS) was observed in SCLC-A compared to SCLC-N (adjusted HR 2.4, 95% CI 1.5-3.9, p &lt; 0.001) and SCLC-P (adjusted HR 1.7, 95% CI 0.9-2.9, p = 0.087). SCLC-TN showed a similar OS with SCLC-A (adjusted HR 1.2, 95% CI 0.6 -2.7, p = 0598). The clinical outcome based on inflamed phenotype, clustered by effector cell gene expression profile which are only found in 5% of SCLC-N but 60% of SCLC-P, was more likely to benefit from first-line immunotherapy treatment than non-inflamed phenotype (p = 0.013). Inflammed phenotype demonstrated longer progression-free survival to the first line immunotherapy compared to the non-inflammed phenotype. (10.5 vs 4.3, p = 0.013)
Conclusions: This study provides fundamental data, including the incidence and basic demographics of molecular subtypes of SCLC using both IHC and WTS from a comparably large cohort including potential differences in the distribution of subtypes based on ethnicity. Additionally, our results reveal differences in the underlying biological pathway activities and immunogenicity based on molecular subtype, possibly related to the difference in clinical outcomes, including immunotherapy response.
Citation Format: Sehhoon Park, Tae Hee Hong, Soohyun Hwang, Hyun-Ae Jung, Jong-Mu Sun, Jin Seok Ahn, Myung-Ju Ahn, Jong Ho Cho, Yong Soo Choi, Jhingook Kim, Young Mog Shim, Hong Kwan Kim, Yoon-La Choi, Se-hoon Lee, Keunchil Park. Comprehensive analysis using transcriptional factor based molecular subtypes and correlation to clinical outcomes in small-cell lung cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4546.