Introduction: The phase 2 TROPiCS-03 study evaluated the efficacy/safety of sacituzumab govitecan (SG) as second-line treatment in patients with previously treated extensive-stage SCLC (ES-SCLC)., Methods: TROPiCS-03 (NCT03964727) is a multicohort, open-label, phase 2 basket study of solid tumors, including ES-SCLC. Adults with ES-SCLC that progressed after one previous line of platinum-based chemotherapy and anti-programmed death-(ligand) 1 (PD-[L]1) therapy received SG 10 mg/kg on days 1 and 8 of a 21-day cycle. The primary end point was the investigator-assessed objective response rate (ORR) according to Response Evaluation Criteria in Solid Tumors version 1.1. Key secondary end points included investigator-assessed duration of response (DOR) and progression-free survival (PFS); blinded independent central review-assessed ORR, DOR, and PFS; overall survival (OS); and safety. Efficacy was evaluated in patients with platinum-resistant and platinum-sensitive disease., Results: Among 43 patients (median follow-up, 12.3 [range, 8.1-20.1] mo), investigator-assessed ORR was 41.9% (95% confidence interval [CI]: 27.0%-57.9%), with 18 confirmed partial responses; median (95% CI) DOR, PFS, and OS were 4.73 (3.52-6.70), 4.40 (3.81-6.11), and 13.60 (6.57-14.78) months, respectively. The efficacy results of the blinded independent central review assessments were similar. The investigator-assessed ORR (95% CI) was 35.0% (15.4%-59.2%) in patients with platinum-resistant disease (n = 20) and 47.8% (26.8%-69.4%) in patients with platinum-sensitive disease (n = 23). Furthermore, 32 patients (74.4%) had grade greater than or equal to 3 treatment-emergent adverse events (TEAEs). No TEAE led to SG discontinuation; one treatment-related TEAE (neutropenic sepsis) led to death., Conclusions: SG has promising efficacy as second-line treatment of ES-SCLC, irrespective of platinum sensitivity. Safety was manageable and consistent with that observed in other SG studies., Competing Interests: Disclosure Dr. Dowlati reports serving on the advisory board with AstraZeneca, Jazz, Seattle Genetics, Bristol Myers Squibb, Prelude Therapeutics, and Puma Biotechnology. Dr. Chiang reports serving on the advisory board with Amgen, AstraZeneca, Daiichi Sankyo, Fosun, Genentech, Janssen, and Zai Labs. Dr. Cervantes reports receiving institutional research funding from AbbVie, Bayer, Beigene, Bristol Myers Squibb, Genentech, HiFiBiO Therapeutics, invoX Pharma, Merck Serono, Merck Sharp & Dohme, Natera, Novartis, Roche, and Servier; serving on the advisory board or receiving speaker fees paid to his institution from AbbVie, Agenus, Arcus Biosciences, GlaxoSmithKline, and Roche. Dr. Babu reports having institutional grants or contracts from 1200 Pharma, AbbVie, Alexion Pharmaceuticals, Amgen, Aptose Biosciences, Argenx, AstraZeneca/MedImmune, Bristol Myers Squibb, Beigene, Genentech/Roche, Gilead Sciences, Janssen Oncology, Lilly, Merck, Nektar, Novartis, Scholar Rock, Sanofi, Syndax, Takeda, TG Therapeutics, and Torl Biotherapeutics; receiving personal consulting fees from Cornerstone Specialty Network, ER Squibb Sons, LLC, Kite (a Gilead Company), Novartis, and Taiho Oncology; receiving personal payment or honoraria for lectures, presentations, speakers’ bureaus, manuscript writing, or educational events from Cornerstone Healthcare Group, Janssen Scientific Affairs, Novartis, and Pfizer; receiving personal support for attending meetings and/or travel from Beigene, Janssen, Karyopharm, Kite (a Gilead Company), and Pharmacyclics; receiving personal support for a leadership or fiduciary role in other board, society, committee or advocacy group, paid or unpaid from Exigent Research; having stock or stock options in Fort Wayne Medical Oncology and Hematology and Lutheran Hospital; and having personal employment at Fort Wayne Medical Oncology and Hematology. Dr. Hamilton reports receiving institutional support for the present manuscript (e.g., funding, provision of study materials, medical writing, article processing charges) from Gilead Sciences; receiving institutional grants or contracts from AbbVie, Acerta Pharma, Accutar Biotechnology, ADC Therapeutics, AKESOBIO Australia, Amgen, Aravive, ArQule, Artios, Arvinas, AstraZeneca, AtlasMedX, BeiGene, Black Diamond, Bliss BioPharmaceuticals, Boehringer Ingelheim, Bristol Myers Squibb, Cascadian Therapeutics, Clovis, Compugen, Context Therapeutics, Cullinan, Curis, CytomX, Daiichi Sankyo, Dana Farber Cancer Institute, Dantari, Deciphera, Duality Biologics, eFFECTOR Therapeutics, Eisai, Ellipses Pharma, Elucida Pharma, EMD Serono, Fochon Pharmaceuticals, FujiFilm, G1 Therapeutics, Gilead Sciences, H3 Biomedicine, Harpoon, Hutchinson MediPharma, Immunogen, Incyte, Infinity Pharmaceuticals, Inspirna, InvestisBio, Jacobio, Karyopharm, K-Group Beta, Kind Pharmaceuticals, Leap Therapeutics, Lilly, Loxo Oncology, Lycera, Mabspace Biosciences, Macrogenics, MedImmune, Mersana, Merus, Millennium, Molecular Templates, Myriad Genetic Laboratories, Novartis, Nucana, Olema, OncoMed, Oncothyreon, ORIC Pharmaceuticals, Orinove, Orum Therapeutics, Pfizer, PharmaMar, Pieris Pharmaceuticals, Pionyr Immunotherapeutics, Plexxikon, Prelude Therapeutics, Profound Bio, Radius Health, Regeneron, Relay Therapeutics, Repertoire Immune Medicine, Rgenix, Roche/Genentech, SeaGen, Sermonix Pharmaceuticals, Shattuck Labs, Silverback Therapeutics, StemCentRx, Stemline Therapeutics, Sutro, Syndax, Syros, Taiho, TapImmune, Tesaro, Tolmar, Torque Therapeutics, Treadwell Therapeutics, Verastem, Zenith Epigenetics, and Zymeworks; and receiving institutional consulting fees from Accutar Biotechnology, AstraZeneca, Daiichi Sankyo, Ellipses Pharma, Entos, Fosun Pharma, Gilead Sciences, Jazz Pharmaceuticals, Jefferies, Lilly, Medical Pharma Services, Mersana, Novartis, Olema Pharmaceuticals, Pfizer, Roche/Genentech, Stemline Therapeutics, Tempus Labs, Theratechnologies, Tubulis, Verascity Science, and Zentalis Pharmaceuticals. Dr. Sullivan reports receiving support for participation on a data safety monitoring board or advisory board from Roche and is an employee of and owns stock in Gilead Sciences, Inc. Dr. van Marcke reports (all institutional compensations) serving on the advisory board with AstraZeneca, Lilly, Merck, and Novartis; receiving research grants from DigiCore and Gilead Sciences, Inc. Dr. Italiano reports having grants or contracts from AstraZeneca, Bayer, Bristol Myers Squibb, Merck, Merck Sharp & Dohme, and Roche; receiving consulting fees from AstraZeneca, Bayer, Domain Therapeutics, Merck, Merck Sharp & Dohme, and Roche; receiving support for attending meetings and/or travel from AstraZeneca and Roche; and receiving support for participation on data safety monitoring boards or advisory boards from AbbVie, Boehringer, Daiichi Sankyo, Merck, Merck Sharp & Dohme, and Roche. Drs. Patel, Mekan, and Wu are employees of and own stock in Gilead Sciences, Inc. Dr. Waqar reports serving on the advisory board for AstraZeneca, Daiichi Sankyo, Gilead Sciences, Inc., Janssen Pharmaceuticals, Boehringer Ingelheim, and Pfizer. The remaining authors declare no conflict of interest., (Copyright © 2025 International Association for the Study of Lung Cancer. Published by Elsevier Inc. All rights reserved.)