Objectives: The lack of definitive biomarkers presents a significant challenge for chemo-immunotherapy in extensive-stage small-cell lung cancer (ES-SCLC). We aimed to identify key genes associated with chemo-immunotherapy efficacy in ES-SCLC through comprehensive gene expression analysis using machine learning (ML)., Methods: A prospective multicenter cohort of patients with ES-SCLC who received first-line chemo-immunotherapy was analyzed. RNA sequencing was performed on tumor samples to assess gene expression levels. ML techniques were applied to identify key gene features associated with treatment efficacy. A panel of genes was then developed and validated using the nCounter system, and the model's performance in predicting 180-day progression-free survival (PFS) was evaluated., Results: A total of 93 patients were included in the analysis. ML-based gene selection identified a gene set comprising 83 genes from the comprehensive gene expression data. An nCounter panel was developed using these genes, and an ML model was developed based on their expression levels. In the validation set, the model achieved an accuracy of 0.93, precision of 1.00, a true positive rate of 0.83, and a true negative rate of 1.00. PFS was significantly longer in the high-efficacy group than in the low-efficacy group in the validation set (P < 0.001)., Conclusions: These findings provide a foundation for biomarker development in ES-SCLC and highlight the potential of this method as a cost-effective, simple, and rapid tool for assessing treatment efficacy in clinical practice., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships, which may be considered potential competing interests:Daichi Fujimoto has received grants and personal fees from AstraZeneca KK and Boehringer Ingelheim Japan Inc., as well as personal fees from Ono Pharmaceutical Co. Ltd., Bristol-Myers Squibb Co. Ltd., Taiho Pharmaceutical Co. Ltd., Chugai Pharmaceutical Co. Ltd., MSD KK, Eli Lilly Japan KK, Novartis Pharma KK, Kyowa Kirin Co. Ltd., and Janssen Pharmaceutical KK, outside of the submitted work. He also participates on an advisory board for AstraZeneca KK and Chugai Pharmaceutical Co. Ltd.Ryota Shibaki has received personal fees from AstraZeneca KK, Chugai Pharmaceutical Co. Ltd., MSD KK, Taiho Pharmaceutical Co. Ltd., Ono Pharmaceutical Co. Ltd., Daiichi Sankyo Co. Ltd., and Boehringer Ingelheim Japan Inc., outside of the submitted work.Keiichi Kimura has received personal fees from Chugai Pharmaceutical Co. Ltd., outside of the submitted work.Koji Haratani has received grants from AstraZeneca K.K., Mochida Memorial Foundation, Nakatomi Foundation, Takeda Science Foundation, The Osaka Medical Research Foundation for Intractable Disease, YOKOYAMA Foundation for Clinical Pharmacology, SGH Foundation, KANAE Foundation for the Promotion of Medical Science, and Osaka Cancer Society, as well as personal fees from AstraZeneca K.K., outside of the submitted work.Motohiro Tamiya has received personal fees from Ono Pharmaceutical, Boehringer Ingelheim, AstraZeneca, Taiho Pharmaceutical, Eli Lilly, Pfizer, Chugai Pharmaceutical, Takeda Pharmaceutical, MSD, Amgen, Bristol-Myers Squibb, and Daiichi Sankyo, outside of the submitted work.Takashi Kijima has received personal fees from Chugai Pharmaceutical Co. Ltd., outside of the submitted work.Yuki Sato has received personal fees from AstraZeneca, MSD, Novartis, Chugai Pharmaceutical, Ono Pharmaceutical, Pfizer, Taiho Pharmaceutical, Nippon Kayaku, Bristol-Myers Squibb, Eli Lilly, Takeda, Kyowa Kirin, Daiichi Sankyo, Boehringer Ingelheim, and Regeneron Pharmaceuticals, outside of the submitted work.Akito Hata has received grants from MSD, Eli Lilly, Chugai, Taiho, Boehringer Ingelheim, AstraZeneca, and AbbVie, as well as personal fees from Eli Lilly, MSD, Chugai, Pfizer, AstraZeneca, Boehringer Ingelheim, and Taiho, outside of the submitted work.Toshihide Yokoyama has received grants from AbbVie GK, AstraZeneca, Boehringer Ingelheim, Bristol-Myers Squibb, Chugai Pharmaceutical, Daiichi Sankyo, Delta-Fly Pharma, Janssen, MSD, Parexel International, and Takeda, as well as personal fees from AstraZeneca, Bristol-Myers Squibb, Chugai Pharmaceutical, Eli Lilly, Merck Biopharma, MSD, Nippon Kayaku, Novartis, Ono Pharmaceutical, Pfizer, and Takeda, outside of the submitted work.Yoshihiko Taniguchi has received personal fees from Ono Pharmaceutical Co. Ltd., AstraZeneca K.K., Chugai Pharmaceutical Co. Ltd., MSD, and Bristol-Myers Squibb K.K., outside of the submitted work.Junji Uchida has nothing to disclose.Hisashi Tanaka has received personal fees from Ono Pharmaceutical Co. Ltd., Bristol-Myers Squibb, AstraZeneca, Chugai Pharmaceutical Co., Boehringer Ingelheim Japan Inc., Pfizer Japan Inc., Takeda, Daiichi Sankyo, MSD K.K., and Amgen, outside of the submitted work.Naoki Furuya has received personal fees from AstraZeneca, Bristol-Myers Squibb, Chugai Pharmaceutical, Eli Lilly, and MSD, outside of the submitted work.Satoru Miura has received personal fees from Chugai Pharmaceutical, Taiho Pharmaceutical, Ono Pharmaceutical, AstraZeneca, Bristol-Myers Squibb, Eli Lilly, Boehringer Ingelheim Japan, and Takeda Pharmaceutical, outside of the submitted work.Mihoko Imaji Onishi has nothing to disclose.Shinya Sakata has received personal fees from AstraZeneca, Chugai Pharmaceutical Co. Ltd., Taiho Pharmaceutical, and Takeda Pharmaceutical, outside of the submitted work.Eisaku Miyauchi has received grants from Chugai Pharmaceutical Co. Ltd. and Eli Lily Japan KK, as well as personal fees from Taiho Pharmaceutical Co. Ltd., Daiichi Sankyo KK, Boehringer Ingelheim Japan Inc., Bristol-Myers Squibb Co. Ltd., Novartis Pharma KK, MSD KK, Kyowa Kirin Co. Ltd., Merck Biopharma Co. Ltd., Pfizer Inc., Ono Pharmaceutical Co. Ltd., Eisai Co. Ltd., Chugai Pharmaceutical Co. Ltd., Amgen Inc., Thermo Fisher Scientific K.K., Nippon Kayaku Co. Ltd., Takeda Pharmaceutical Co. Ltd., Eli Lilly Japan KK, Sysmex Co. Ltd., AstraZeneca K.K., and KYORIN Pharmaceutical Co. Ltd., outside of the submitted work. He also participates on an advisory board for Chugai Pharmaceutical Co. Ltd, Boehringer Ingelheim Japan Inc., Eli Lilly Japan KK, Merck Biopharma Co. Ltd., Daiichi Sankyo KK, and Ono Pharmaceutical Co. Ltd.Nobuyuki Yamamoto has received grants from A2 Healthcare Corporation, Amgen K.K., AstraZeneca K.K., Eli Lilly Japan K.K., Mebix Inc., AbbVie GK, Janssen Pharmaceutical K.K., Bristol-Myers Squibb, RPM Co. Ltd., Pfizer R&D Japan G.K., Chugai Pharmaceutical Co. Ltd., MSD K.K., Nippon Boehringer Ingelheim Co. Ltd., PRiME-R Inc., IQVIA Solutions Japan G.K., Novartis Japan, EPS Corporation, Medpace Japan K.K., and Syneos Health Clinical K.K., as well as personal fees from Amgen K.K., AstraZeneca K.K., Chugai Pharmaceutical Co. Ltd., AbbVie GK, Janssen Pharmaceutical K.K., Accuray Japan K.K., Guardant Health Japan Corp., TAIHO ONCOLOGY INC., Tsumura & Co., Nippon Kayaku Co. Ltd., Merck Biopharma Co. Ltd., Otsuka Pharmaceutical Co. Ltd., Miyarisan Pharmaceutical Co. Ltd., Kyowa Kirin Co. Ltd., ShiftZero K.K., MSD K.K., Nippon Boehringer Ingelheim Co. Ltd., Eli Lilly Japan K.K., Novartis Japan, Bristol-Myers Squibb, Ono Pharmaceutical Co. Ltd., Daiichi Sankyo Inc., Takeda Pharmaceutical Co. Ltd., Terumo Co. Ltd., Pfizer Japan Inc., USACO Corporation, KYORIN Pharmaceutical Co. Ltd., Medical Review Co. Ltd., and KOWA COMPANY LTD., outside of the submitted work. He also participates on advisory boards for Amgen K.K., Daiichi Sankyo Inc., USACO Corporation, AstraZeneca K.K., Ono Pharmaceutical Co. Ltd., and Novartis Japan.Yasuhiro Koh has received grants from Chugai Pharmaceutical Co. Ltd. and personal fees from Chugai Pharmaceutical Co. Ltd., outside of the submitted work.Hiroaki Akamatsu has received grants from Amgen Inc. and Chugai Pharmaceutical Co. Ltd., as well as personal fees from Amgen Inc., AstraZeneca K.K., Boehringer Ingelheim Japan Inc., Bristol-Myers Squibb, Chugai Pharmaceutical Co. Ltd., Eli Lilly Japan K.K., MSD K.K., Nippon Kayaku Co. Ltd., Novartis Pharma K.K., Ono Pharmaceutical Co. Ltd., Pfizer Inc., Takeda Pharmaceutical Co. Ltd., Taiho Pharmaceutical Co. Ltd., and Daiichi Sankyo, outside of the submitted work. He also participates on advisory boards for Amgen Inc., MSD, Janssen Pharmaceutical K.K., and Sandoz., (Copyright © 2024. Published by Elsevier B.V.)