Background: The development of targeted agents, such as osimertinib for EGFR-mutated non-small-cell lung cancer (NSCLC), has drastically improved patient outcome, but tumor resistance eventually always occurs. In osimertinib-resistant NSCLC, the emergence of a second molecular driver alteration (such as ALK, RET, FGFR3 fusions or BRAF, KRAS mutations) has been described. Whether those alterations and the activating EGFR mutations occur within a single cancer cell or in distinct cell populations is largely debated., Patients and Methods: Tumor sequencing was used to identify the acquired resistance mechanisms to osimertinib in the MATCH-R trial (NCT0251782). We implemented single-cell next-generation sequencing to investigate tumor heterogeneity on patient's frozen tissues in which multiple alterations have been identified. Patient-derived models, cell lines, and patient-derived xenografts were exposed to specific inhibitors to investigate combination treatment strategies., Results: Among the 45 patients included in MATCH-R who progressed on osimertinib, 9 developed a second targetable alteration (n = 2 FGFR3-TACC3, n = 1 KIF5B-RET, n = 1 STRN-ALK fusions; n = 2 BRAF V600E , n = 1 KRAS G12V , n = 1 KRAS G12R , n = 1 KRAS G12D mutations). Single-cell analysis revealed that the two driver alterations coexist within one single cancer cell in the four patients whose frozen samples were fully contributive. A high degree of heterogeneity within samples and sequential acquisitions of molecular events were highlighted. A combination treatment concomitantly targeting the two driver alterations was required on the corresponding patient-derived models to restore cell sensitivity, which was consistent with clinical data showing efficacy of brigatinib in the patient with ALK fusion after progression to osimertinib and crizotinib administered sequentially., Conclusions: Distinct molecular driver alterations at osimertinib resistance coexist with initial EGFR mutations in single cancer cells. The clonal evolution of cancer cell populations emphasized their heterogeneity leading to osimertinib relapse. Combining two targeted treatments is effective to achieve clinical benefit., Competing Interests: Disclosure AG Principal/sub-investigator of Clinical Trials for Abbvie, Adaptimmune, Adlai Nortye USA Inc., Aduro Biotech, Agios Pharmaceuticals, Amgen, Argen-X Bvba, Arno Therapeutics, Astex Pharmaceuticals, AstraZeneca Ab, Aveo, Basilea Pharmaceutica International Ltd., Bayer Healthcare Ag, Bbb Technologies Bv, Beigene, BicycleTx Ltd., Bioalliance Pharma, Blueprint Medicines, Boehringer Ingelheim, Boston Pharmaceuticals, Bristol-Myers Squibb, Ca, Celgene Corporation, Chugai Pharmaceutical Co, Cullinan-Apollo, Curevarc, Daiichi Sankyo, Debiopharm, Eisai, Eisai Limited, Eli Lilly, Exelixis, Faron Pharmaceuticals Ltd., Forma Tharapeutics, Gamamabs, Genentech, GlaxoSmithKline, H3 Biomedicine, Hoffmann La Roche Ag, Imcheck Therapeutics, Innate Pharma, Institut De Recherche Pierre Fabre, Iris Servier, Iteos Belgium SA, Janssen Cilag, Janssen Research Foundation, Kura Oncology, Kyowa Kirin Pharm. Dev, Lilly France, Loxo Oncology, Lytix Biopharma As, Medimmune, Menarini Ricerche, Merck Sharp & Dohme Chibret, Merus, Molecular Partners Ag, Nanobiotix, Nektar Therapeutics, Novartis Pharma, Octimet Oncology Nv, Oncoethix, Oncopeptides, Onyx Therapeutics, Orion Pharma, Oryzon Genomics, Ose Pharma, Pfizer, Pharma Mar, Pierre Fabre Medicament, Plexxikon, Roche, Sanofi Aventis, Seattle Genetics, Sotio A.S, Syros Pharmaceuticals, Taiho Pharma, Tesaro, Turning Point Therapeutics, Xencor Research Grants from AstraZeneca, BMS, Boehringer Ingelheim, GSK, INCA, Janssen Cilag, Merck, Novartis, Pfizer, Roche, Sanofi, non-financial support (drug supplied) from AstraZeneca, Bayer, BMS, Boringher Ingelheim, GSK, Medimmune, Merck, NH TherAGuiX, Pfizer, Roche. SM Outside the scope of the submitted work: statistical advice to IDDI, Janssen Cilag, Amaris, Roche; data and safety monitoring member of clinical trials: Sensorion, Biophytis, Servier, Yuhan Bye. SP research grants: Merck Sharp and Dohme, F. Hoffmann-La Roche, Foundation Medicine, PharmaMar. Personal fees: Merck Sharp and Dohme, Bristol-Myers Squibb, F. Hoffmann-La Roche, Foundation Medicine, AstraZeneca, Boehringer Ingelheim, Eli Lilly, Pfizer, Amgen, Celgene. Non-financial support: Merck Sharp and Dohme, Bristol-Myers Squibb, F. Hoffmann-La Roche. FF Personal fees: Bristol-Myers Squibb, F. Hoffmann-La Roche, BeiGene. LT Research grants: BMS foundation, Terumo. Consulting and personal fees: Boston Scientific, GE healthcare, IPSEN, Quantum Surgical. FB Personal fees from AstraZeneca, Bayer, Bristol-Myers Squibb, Boehringer Ingelheim, Eli Lilly Oncology, F. Hoffmann-La Roche Ltd., Novartis, Merck, MSD, Pierre Fabre, Pfizer and Takeda. LF Research funding from Debiopharm, Incyte, Relay Therapeutics. DP Consulting, advisory role or lectures: AstraZeneca, Bristol-Myers Squibb, Boehringer Ingelheim, Celgene, Daiichi Sankyo, Eli Lilly, Merck, Novartis, Pfizer, prIME Oncology, Peer CME, Roche, Janssen, Abbvie; Honoraria: AstraZeneca, Bristol-Myers Squibb, Boehringer Ingelheim, Celgene, Eli Lilly, Merck, Novartis, Pfizer, prIME Oncology, Peer CME, Roche, Janssen, Abbvie. Clinical trials research as principal or co-investigator (Institutional financial interests): AstraZeneca, Bristol-Myers Squibb, Boehringer Ingelheim, Eli Lilly, Merck, Novartis, Pfizer, Roche, Medimmun, Sanofi-Aventis, Taiho Pharma, Novocure, Daiichi Sankyo, Janssen, Abbvie Travel, Accommodations, Expenses: AstraZeneca, Roche, Novartis, prIME Oncology, Pfizer. BB Sponsored Research at Gustave Roussy Cancer Center: 4D Pharma, Abbvie, Amgen, Aptitude Health, AstraZeneca, BeiGene, Blueprint Medicines, BMS, Boehringer Ingelheim, Celgene, Cergentis, Cristal Therapeutics, Daiichi Sankyo, Eli Lilly, GSK, Inivata, Janssen, Onxeo, OSE immunotherapeutics, Pfizer, Roche-Genentech, Sanofi, Takeda, Tolero Pharmaceuticals. JCS In the last 2 years consultancy fees and shares from: Relay Therapeutics, Gritstone bio; Board of Directors Hookipa Pharmaceuticals 2018-2021; Full time employee at AstraZeneca 2017-2019; Full time employee at Amgen August 2021-present. All other authors have declared no conflicts of interest., (Copyright © 2022 The Author(s). Published by Elsevier Ltd.. All rights reserved.)