Following the approval of the first antibody-drug conjugates (ADCs) in the early 2000s, development has increased dramatically, with 14 ADCs now approved and >100 in clinical development. In lung cancer, trastuzumab deruxtecan (T-DXd) is approved in human epidermal growth factor receptor 2 (HER2)-mutated, unresectable or metastatic non-small-cell lung cancer, with ADCs targeting HER3 (patritumab deruxtecan), trophoblast cell-surface antigen 2 [datopotamab deruxtecan and sacituzumab govitecan (SG)] and mesenchymal-epithelial transition factor (telisotuzumab vedotin) in late-stage clinical development. In breast cancer, several agents are already approved and widely used, including trastuzumab emtansine, T-DXd and SG, and multiple late-stage trials are ongoing. Thus, in the coming years, we are likely to see significant changes to treatment algorithms. As the number of available ADCs increases, biomarkers (of response and resistance) to better select patients are urgently needed. Biopsy sample collection at the time of treatment selection and incorporation of translational research into clinical trial designs are therefore critical. Biopsy samples taken peri- and post-ADC treatment combined with functional genomics screens could provide insights into response/resistance mechanisms as well as the impact of ADCs on tumour biology and the tumour microenvironment, which could improve understanding of the mechanisms underlying these complex molecules. Many ADCs are undergoing evaluation as combination therapy, but a high bar should be set to progress clinical evaluation of any ADC-based combination, particularly considering the high cost and potential toxicity implications. Efforts to optimise ADC dosing/duration, sequencing and the potential for ADC rechallenge are also important, especially considering sustainability aspects. The ETOP IBCSG Partners Foundation are driving strong collaborations in this field and promoting the generation/sharing of databases, repositories and registries to enable greater access to data. This will allow the most important research questions to be identified and prioritised, which will ultimately accelerate progress and help to improve patient outcomes., Competing Interests: Disclosure SP reports receipt of institutional educational grants and honoraria (all fees to institution) for consultation, attending advisory boards and/or providing lectures for the following organisations: consultation/advisory role: AbbVie, AiCME, Amgen, Arcus, AstraZeneca, Bayer, Beigene, BerGenBio, Biocartis, BioInvent, Blueprint Medicines, Boehringer Ingelheim, Bristol-Myers Squibb (BMS), Clovis, Daiichi Sankyo, Debiopharm, ecancer, Eli Lilly, Elsevier, F-Star, Fishawack, Foundation Medicine, Genzyme, Gilead, GSK, Illumina, Imedex, IQVIA, Incyte, Ipsen, iTeos, Janssen, Medscape, Medtoday, Merck Sharp & Dohme (MSD), Merck Serono, Merrimack, Mirati, Novartis, Novocure, OncologyEducation, Pharma Mar, Phosplatin Therapeutics, PER, Peerview, Pfizer, Regeneron, RMEI, Roche/Genentech, RTP, Sanofi, Seattle Genetics, Takeda, Vaccibody; Board of Director role: Galenica SA; presentation at a company-organised public event: AiCME, AstraZeneca, Boehringer Ingelheim, BMS, ecancer, Eli Lilly, Foundation Medicine, GSK, Illumina, Imedex, Ipsen, Medscape, MSD, Mirati, Novartis, PER, Peerview, Pfizer, Roche/Genentech, RTP, Sanofi, Takeda; receipt of grants/research support: principal investigator in trials (institutional financial support for clinical trials) sponsored by Amgen, AstraZeneca, Beigene, BMS, GSK, MSD, Roche/Genentech. SL reports receipt of research funding to institution from Novartis, BMS, Merck Sharp & Dohme (MSD), Puma Biotechnology, Eli Lilly, Nektar Therapeutics, AstraZeneca/Daiichi Sankyo, Seattle Genetics; has acted as consultant (not compensated) to Seattle Genetics, Novartis, BMS, MSD, AstraZeneca/Daiichi Sankyo, Eli Lilly, Pfizer, Gilead Therapeutics, Nektar Therapeutics, PUMA Biotechnologies, Roche-Genentech; has acted as consultant (paid to institution) to Novartis, GSK, Roche-Genentech, AstraZeneca/Daiichi Sankyo, Gilead Sciences, Seattle Genetics, MSD, Eli Lilly, BMS. FA reports research grants (compensated to the hospital) from AstraZeneca, Daiichi Sankyo, Roche, Lilly, Pfizer, Owkin, Novartis, Guardant Health; honoraria (compensated to the hospital) for advisory board participation or speaker activities from AstraZeneca, Daiichi Sankyo, Roche, Lilly, Pfizer, Owkin, Novartis, Guardant Health, N-Power Medicine, SERVIER, Gilead, Boston Pharmaceutics; personal honoraria for advisory board participation from Lilly. SC reports receipt of personal consulting fees from Novartis, AstraZeneca, Nuvalent, Genesis Therapeutics, Effector Therapeutics, SAGA Diagnostics, Prelude Therapeutics, Gerson Lehman Group; stock options from Effector Therapeutics, Odyssey Biosciences; research funding from AstraZeneca, Daiichi Sankyo. EF reports receipt of personal speaker honoraria from Amgen, AstraZeneca, BMS, Daiichi Sankyo, Eli Lilly, F. Hoffmann-La Roche, Genentech, Janssen, Medical Trends, Medscape, Merck Serono, MSD, Peervoice, Pfizer, Sanofi, Takeda, Touch Oncology; personal honoraria for advisory board participation from AbbVie, Amgen, AstraZeneca, Bayer, Beigene, Boehringer Ingelheim, BMS, Eli Lilly, F. Hoffmann-La Roche, Gilead, GSK, Janssen, Merck Serono, MSD, Novartis, Peptomyc, Pfizer, Regeneron, Sanofi, Takeda, Turning Point, Daiichi Sankyo; financial support for meeting attendance and/or travel from AstraZeneca, Janssen, Roche. SPF reports receipt of personal honoraria for advisory board participation from Amgen, AstraZeneca, Illumina, Pfizer; honoraria to institution for advisory board participation from Roche; personal speaker honoraria from Takeda; holds personal stocks/shares in Revolution Medicines. PAJ reports receipt of grants and personal fees from AstraZeneca, Boehringer Ingelheim; personal fees from Pfizer, Roche/Genentech, Chugai Pharmaceuticals, Loxo Oncology; grants and personal fees from Eli Lilly; personal fees from SFJ Pharmaceuticals, Voronoi; grants and personal fees from Daiichi Sankyo; personal fees from Biocartis, Novartis, Sanofi, Scorpion Therapeutics, Merus, Frontier Medicines, Hongyun Biotechnology, Duality Biologics, Blueprint Medicines, Phanes Therapeutics; grants and personal fees from Takeda Oncology; personal fees from Mirati Therapeutics, Transcenta, Silicon Therapeutics, Syndax, Nuvalent, Bayer, Eisai, Allorion Therapeutics, Accutar Biotech, AbbVie; grants from Revolution Medicines; grants from PUMA; grants from Astellas, outside the submitted work. In addition, PAJ is a co-inventor on a DFCI patent on EGFR mutations and receives post-marketing royalties from Lab Corp. KMK reports receipt of personal consultancy fees from AbbVie, Amgen, AstraZeneca, Bayer, Boehringer Ingelheim, BMS, Daiichi Sankyo, Janssen, Merck Serono, Merck Sharp & Dohme, Novartis, Pfizer, Regeneron, Roche, Sanofi, Takeda, Ventana; personal speaker honoraria from AbbVie, AstraZeneca, Amgen, Boehringer Ingelheim, BMS, Janssen, Merck Serono, Merck Sharp & Dohme, Mirati, Novartis, Pfizer, Roche, Sanofi, Ventana, Medscape, Mirati, Prime Oncology, PeerVoice, PER. EM reports receipt of personal honoraria for consulting/advisory roles to Exact Sciences, MSD Oncology, Daiichi Sankyo/AstraZeneca, Pfizer, Seagen, Ipsen; reimbursement of travel, accommodation and expenses from Roche, Pfizer, Lilly, Novartis, Gilead Sciences, AstraZeneca, Pierre Fabre. AP reports receipt of personal honoraria for consulting or an advisory role for AstraZeneca, Bayer, BMS, Boehringer Ingelheim, Daiichi Sankyo, Lilly, GSK, Janssen, MSD, Mundipharma, Novartis, Roche; speakers bureaus for AstraZeneca, Boehringer Ingelheim, Daiichi Sankyo, eCancer, Janssen, MSD, Medscape, PeerVoice, touchONCOLOGY. MP reports receipt of personal honoraria for consultancy to Roche, Eli Lilly, Pfizer, Boehringer Ingelheim, MSD, BMS, Novartis, AstraZeneca, Takeda, Gritstone, Sanofi, GSK, Amgen, AbbVie, Ipsen, Esaï, Daiichi Sankyo, Janssen, AnHeart Therapeutics, Novocure; lecture fees from Eli Lilly, Roche, AstraZeneca, Pfizer, Amgen, Boehringer Ingelheim, BMS, Takeda, MSD, Chugai, Illumina, Sanofi, Janssen; research grants (paid to institution) from Roche, AstraZeneca, Takeda, Boehringer Ingelheim. EFS reports consultancy fees (paid to institution) from AstraZeneca, BMS, Boehringer Ingelheim, Daiichi Sankyo, Eli Lilly, Janssen, MSD, Roche Sanofi, Takeda; personal honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from Boehringer Ingelheim, Daiichi Sankyo; participation on a Data Safety Monitoring Board for DSI. CS reports grants from AstraZeneca, Boehringer Ingelheim, BMS, Pfizer, Roche-Ventana, Invitae (previously Archer Dx Inc.), Ono Pharmaceutical, Personalis; is Chief Investigator and Steering Committee Chair for the AZ MeRmaiD 1 and 2 clinical trials; is Co-Chief Investigator of the NHS Galleri trial funded by GRAIL and a paid member of GRAIL’s Scientific Advisory Board; has received consultancy fees from Achilles Therapeutics (also SAB member), Bicycle Therapeutics (also SAB member), Genentech, Medicxi, China Innovation Centre of Roche (CICoR) formerly Roche Innovation Centre—Shanghai, Metabomed (until July 2022), Relay Therapeutics SAB member, Saga Diagnostics SAB member, the Sarah Cannon Research Institute; has received honoraria from Amgen, AstraZeneca, BMS, GSK, Illumina, MSD, Novartis, Pfizer, Roche-Ventana; has previously held stock options in Apogen Biotechnologies and GRAIL, currently has stock options in Epic Bioscience and Bicycle Therapeutics, and has stock options and is co-founder of Achilles Therapeutics; declares a patent application (PCT/US2017/028013) for methods to lung cancer, targeting neoantigens (PCT/EP2016/059401), identifying patent response to immune checkpoint blockade (PCT/EP2016/071471), methods for lung cancer detection (US20190106751A1), identifying patients who respond to cancer treatment (PCT/GB2018/051912), determining HLA LOH (PCT/GB2018/052004), predicting survival rates of patients with cancer (PCT/GB2020/050221), methods for systems and tumour monitoring (PCT/EP2022/077987); is an inventor on a European patent application (PCT/GB2017/053289) relating to assay technology to detect tumour recurrence—this patent has been licensed to a commercial entity and under their terms of employment, he is due a share of any revenue generated from such license(s). GV reports receipt of honoraria for consulting and participation in advisory boards from Roche, AstraZeneca, Daiichi Sankyo, Gilead, Pfizer and Agilent. RAS reports receipt of personal speaker honoraria from Amgen, AstraZeneca, Boehringer Ingelheim, Roche; honoraria for advisory board participation from AstraZeneca, Eisai, GSK, Guardant, Janssen, Merck, MSD, Novocure, Pfizer, Pharmamar, Roche; financial compensation for his role as Editor for CTR and Editor in Chief for Lung Cancer; receipt of institutional research grants for ETOP and/or IBCSG studies from Amgen, AstraZeneca, BMS, Celgene, Ipsen, Janssen, Mirati, MSD, Novartis, Pfizer, Pierre Fabre, Roche; is an ETOP IBCSG Partners Foundation Member and President of the Board of Directors (uncompensated)., (Copyright © 2024 European Society for Medical Oncology. All rights reserved.)