Introduction: Tarlatamab demonstrated a durable response and promising survival outcomes in patients with previously treated small cell lung cancer (SCLC) in the phase 2, open-label DeLLphi-301 trial. Patient-reported outcomes (PROs) were evaluated to assess the benefit-risk profile of tarlatamab., Methods: Patients received tarlatamab intravenously every 2 weeks at a dose of 10 mg (regulatory approved dose) or 100-mg until progression or loss of benefit. PROs, including European Organization for Research and Treatment of Cancer 30-item Quality of Life Questionnaire (EORTC-QLQ-C30) and 13-item lung cancer module (LC13), Patient-Reported Outcomes Version of the Common Terminology Criteria for Adverse Events (PRO-CTCAE), and the GP5 question of the Functional Assessment of Cancer Therapy - General Form (FACT-GP5), were collected at Cycle 1 (days 1, 8, 22), Cycle 2 (days 1, 15) and every 6 weeks from Cycle 3 onwards. PROs were summarized descriptively alongside the amount and reason for missing data and analyzed using a mixed model for repeated measures. In addition, median time to deterioration (TTD) for symptom and functional scales was analyzed., Results: A total of 100 patients were PRO-evaluable at the selected target dose (10 mg). EORTC-QLQ-C30 and LC13 completion rates (proportion of PRO assessments expected to be completed) were high (> 80%) throughout the study. Least square mean changes from baseline showed a trend towards improvement for the QLQ-C30 subscale of global health status and stabilization for physical functioning. Patients experienced reduced symptom burden for dyspnea which was more pronounced for patients at later cycles (≥ 10 points), and stabilization for chest pain and cough. Median TTD exceeded 6 months for cough and dyspnea and was not estimable for chest pain. Overall, tarlatamab was well tolerated with the majority of patients reporting no bother or a little bit of bother from side effects post baseline. Patient-reported adverse events were generally of mild to moderate severity occurring rarely or occasionally., Conclusion: Alongside previously reported antitumor activity, tarlatamab demonstrated a positive benefit-risk profile in previously treated SCLC with favorable PROs across a range of functional outcomes and symptoms, while showing manageable and sustained tolerability., Gov Number: NCT05060016., Competing Interests: Declarations. Conflict of Interest: Horst-Dieter Hummel reports consultancy work and steering board membership, support for attending meetings, and participation on a data safety monitoring board with Amgen. Myng-Ju Ahn received consultancy fees from Amgen, Astra-Zeneca, Daiichi-Sankyo, Eli Lilly, F. Hoffman-La-Roche, Merck, Merck KGaA, and is employed as a professor of the Samsung Medical Centre. Fiona Blackhall reports consulting fees and payment or honoraria from Amgen and AstraZeneca. Martin Reck has been a paid member speaker bureau and/or consultant for Amgen, AstraZeneca AB, BeiGene USA Inc, Boehringer Ingelheim, Bristol Myers Squibb Company, Daiichi Sankyo Company LTD Eli Lilly F. Hoffmann-La Roche, GlaxoSmithKline, Merck Sharp and Dohme, Pfizer, Regeneron Pharmaceuticals, and conducted Data and Safety Monitoring for Sanofi. Hiroaki Akamatsu received honoraria from Amgen Inc, AstraZeneca K.K., Boehringer Ingelheim Japan Inc., Bristol-Myers Squibb, Chugai Pharmaceutical Co. Ltd., Daiichi Sankyo 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 Pharmatheutical Co. Ltd. and Taiho Pharmaceutical Co. Ltd.. He served as an advisor role for Amgen Inc, Janssen Pharmaceutical K.K., and Sandoz. He received research funding from Amgen Inc, Chugai Pharmaceutical Co. Ltd., and MSD K.K. Suresh Ramalingan reports consultancy fees from Amgen, AstraZeneca, Bristol-Myers Squibb, GlaxoSmithKine, Merck, Takeda Oncology. Hossein Borghaei reports research support (Clinical Trials) from BMS, Lilly, Amgen; Advisory16 Board/Consultant role for BMS, Lilly, Genentech, Pfizer, Merck, EMD-Serono, Boehringer Ingelheim, Astra Zeneca, Novartis, Genmab, Regeneron, BioNTech, Amgen, Axiom, PharmaMar, Takeda, Mirati, Daiichi, Guardant, Natera, Oncocyte, Beigene, iTEO, Jazz, Janssen, DaVolterra; Data and Safety Monitoring Board participation with University of Pennsylvania: CAR T Program, Takeda, Incyte, Novartis; employment with Fox Chase Cancer Center; Scientific Advisory Board participation with Sonnetbio (Stock Options); Inspirna (formerly Rgenix, Stock Options); Nucleai (stock options); Honoraria from Amgen, Pfizer, Daiichi, Regeneron; Travel support from Amgen, BMS, Merck, Lilly, EMD-Serono, Genentech, Regeneron. Melissa Johnson reports a grant or contract for research on behalf of AbbVie, Acerta Pharma, Adaptimmune, Amgen, Apexigen, Arcus Biosciences, Array Biopharma, ArriVent BioPharma, Artios Pharma, AstraZeneca, Atreca, BeiGene, BerGenBio, BioAtla, Black Diamond, Boehringer Ingelheim, Calithera Biosciences, Carisma Therapeutics, Checkpoint Therapeutics, City of Hope National Medical Center, Corvus Pharmaceuticals, Curis, CytomX, Daiichi Sankyo Company, Dracen Pharmaceuticals, Dynavax Technologies, Eli Lilly and Company, Elicio Therapeutics, EMD Serono, EQRx, Erasca, Exelixis, Fate Therapeutics, Genentech USA, Inc, Genmab, Genocea Biosciences, GlaxoSmithKline, Gritstone Oncology, Guardant Health, Harpoon, Helsinn Healthcare SA, Hengrui Therapeutics, Hutchinson MediPharma, IDEAYA Biosciences, IGM Biosciences, Immunitas Therapeutics, Immunocore, Incyte Corporation, Janssen Research & Development, LLC, Jounce Therapeutics, Kadmon Pharmaceuticals LLC, Kartos Therapeutics, LockBody Therapeutics, Loxo Oncology, Lycera, Memorial Sloan-Kettering Cancer Center, Merck, Merus, Mirati Therapeutics, Mythic Therapeutics, NeoImmune Tech, Neovia Oncology, Novartis, Numab Therapeutics, Nuvalent, OncoMed Pharmaceutical, Palleon Pharmaceuticals, Pfizer, PMV Pharmaceuticals, Rain Therapeutics, RasCal Therapeutics, Regeneron Pharmaceuticals, Inc, Relay Therapeutics, Revolution Medicines, Ribon Therapeutics, Rubius Therapeutics, SANOFI US SERVICES INC, Seven and Eight Bipharmaceuticals, Shattuck Labs, Silicon Therapeutics, Stem Centrx, Syndax Pharmaceuticals, Takeda Pharmaceuticals America, Inc, Tarveda, TCR2 Therapeutics, Tempest Therapeutics, Tizona Therapeutics, TMUNITY Therapeutics, Turning Point Therapeutics, University of Michigan, Vyriad, WindMIL Therapeutics, Y-mAbs Therapeutics, Melissa Johnson also reports consultancy fees from AbbVie, Amgen, Astellas Pharma, AstraZeneca, Boehringer Ingelheim, Bristol-Myers Squibb, Calithera Biosciences, D3 Bio Limited, Daiichi Sankyo Company, EcoR1, Fate Therapeutics, Genentech USA, Inc, Genmab, Genocea Biosciences, Gilead Sciences, Inc, GlaxoSmithKline, Gritstone Oncology, IDEAYA Biosciences, Immunocore, Janssen Research & Development, LLC, Jazz Pharmaceuticals Inc, Merck, Mirati Therapeutics, Molecular Axiom, Normunity, Pyramid Biosciences, Regeneron Pharmaceuticals, Revolution Medicines, SANOFI-AVENTIS U.S. LLC, Seagen Inc, Synthekine, Takeda Pharmaceutical Company, and VBL Therapeutics. Franziska Dirnberger is an employee of Amgen and owns Amgen stocks. Kim Cocks is an employee of Adelphi Values who received consultancy fees for the conduct of the analyses and medical writing. Shuang Huang is an employee of Amgen and owns Amgen stocks. Sujoy Mukherjee is an employee of Amgen and owns Amgen stocks. Luis Paz-Ares: Financial Interests, Personal, Advisory Board, Speaker fees: Roche, MSD, BMS, AZ, Lilly, PharmaMar, Beigene, Daiichi, Medscape, PER; Financial Interests, Personal, Advisory Board: Merck Serono, Pfizer, Bayer, Amgen, Janssen, GSK, Novartis, Takeda, Sanofi, Mirati; Financial Interests, Personal, Other, Board member: Genomica, Altum sequencing; Financial Interests, Institutional, Invited Speaker: Daiichi Sankyo, AstraZeneca, Merck Sharp & Dohme Corp, BMS, Janssen-Cilag International25 NV, Novartis, Roche, Sanofi, Tesaro, Alkermes, Lilly, Takeda, Pfizer, PharmaMar; Financial Interests, Personal, Invited Speaker: Amgen; Financial Interests, Other, Member: AACR, ASCO, ESMO; Financial Interests, Other, Foundation Board Member: AECC; Financial Interests, Other, President: ASEICA (Spanish Association of Cancer Research); Financial Interests, Other, Foundation President: ONCOSUR; Financial Interests, Other, member: Small Lung Cancer Group. Ethical Approval: The trial was conducted in accordance with the International Council for Harmonisation Good Clinical Practice guidelines and the principles of the Declaration of Helsinki (WCG (approval number 20233898). The protocol and amendments were approved by the institutional review board at each participating site and by regulatory authorities in the participating countries. All the patients provided written informed consent. A data-review team external to the trial team provided oversight of safety throughout the trial., (© 2025. The Author(s).)