Background: Changes in the management of patients with cancer and delays in treatment delivery during the COVID-19 pandemic may impact the use of hospital resources and cancer mortality., Patients and Methods: Patient flows, patient pathways and use of hospital resources during the pandemic were simulated using a discrete event simulation model and patient-level data from a large French comprehensive cancer centre's discharge database, considering two scenarios of delays: massive return of patients from November 2020 (early-return) or March 2021 (late-return). Expected additional cancer deaths at 5 years and mortality rate were estimated using individual hazard ratios based on literature., Results: The number of patients requiring hospital care during the simulation period was 13,000. In both scenarios, 6-8% of patients were estimated to present a delay of >2 months. The overall additional cancer deaths at 5 years were estimated at 88 in early-return and 145 in late-return scenario, with increased additional deaths estimated for sarcomas, gynaecological, liver, head and neck, breast cancer and acute leukaemia. This represents a relative additional cancer mortality rate at 5 years of 4.4 and 6.8% for patients expected in year 2020, 0.5 and 1.3% in 2021 and 0.5 and 0.5% in 2022 for each scenario, respectively., Conclusions: Pandemic-related diagnostic and treatment delays in patients with cancer are expected to impact patient survival. In the perspective of recurrent pandemics or alternative events requiring an intensive use of limited hospital resources, patients should be informed not to postpone care, and medical resources for patients with cancer should be sanctuarised., Competing Interests: Conflict of interest statement The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: No author reported potential conflict of interest in link with the submitted work. A.B. reports personal fees from Roche SAS. I.B. reports personal fees from Roche, Novartis, CSL Behring and Takeda. M.F. reports fees from HRA Pharma (participation to board) and travel grants from Ipsen, Pfizer and Novartis. S.D. reports grants and non-financial support from Pfizer, grants from Novartis, grants and non-financial support from AstraZeneca, grants and non-financial support from Roche Genentech, grants from Lilly, grants from Puma, grants from Myriad, grants from Orion, grants from Amgen, grants from Sanofi, grants from Genomic Health, grants from GE, grants from Servier, grants from MSD, grants from BMS, grants from Pierre Fabre, grants from Seagen and grants from Exact Sciences. L.A. reports a consulting/advisory role for Novartis (Institution), Amgen (Institution), Bristol Myers Squibb (Institution), Ipsen (Institution), Roche (Institution), Pfizer (Institution), Astellas Pharma (Institution), Merck (Institution), MSD (Institution), AstraZeneca (Institution), Exelixis (Institution), Corvus Pharmaceuticals (Institution) and Peloton Therapeutics (Institution) and research Funding from Bristol Myers Squibb (Institution). D.P. reports a consulting, advisory role or lectures for AstraZeneca, Bristol Myers Squibb, Boehringer Ingelheim, Celgene, Daiichi Sankyo, Eli Lilly, Merck, Novartis, Pfizer, prIME Oncology, Peer CME, Roche and Samsung; honoraria from AstraZeneca, Bristol Myers Squibb, Boehringer Ingelheim, Celgene, Eli Lilly, Merck, Novartis, Pfizer, prIME Oncology, Peer CME, Roche and Samsung; institutional financial interests (clinical trials research as the principal or co-investigator) from AstraZeneca, Bristol Myers Squibb, Boehringer Ingelheim, Eli Lilly, Merck, Novartis, Pfizer, Roche, MedImmune, Sanofi-Aventis, Taiho Pharma, Novocure and Daiichi Sankyo and travel and accommodation expenses from AstraZeneca, Roche, Novartis, prIME Oncology and Pfizer. M.D. reports honoraria for advisory boards or as a presenter in symposium from Merck Serono, MSD, AMGEN, Roche, Bayer, Ipsen, Pfizer, Servier, Pierre Fabre, HalioDx, Lilly and Sanofi. E.C. reports consulting advisory board activity for BMS, Ipsen, Sanofi, Pfizer, GSK and Merck. C.R. reports a consultant/advisory role for Bristol Myers Squibb, MSD, Roche, Novartis, Amgen, Sanofi and Pierre Fabre. C.M. reports consultant/advisory fees from Amgen, Astellas, AstraZeneca, Bayer, BeiGene, BMS, Celgene, Debiopharm, Genentech, Ipsen, Janssen, Lilly, MedImmune, MSD, Novartis, Pfizer, Roche, Sanofi and Orion and as acted as a principal/sub-investigator of clinical trials for AbbVie, Aduro, Agios, Amgen, Argen-x, Astex, AstraZeneca, Aveo pharmaceuticals, Bayer, BeiGene, Blueprint, BMS, Boehringer Ingelheim, Celgene, Chugai, Clovis, Daiichi Sankyo, Debiopharm, Eisai, Eos, Exelixis, Forma, GamaMabs, Genentech, Gortec, GSK, H3 Biomedecine, Incyte, Innate Pharma, Janssen, Kura Oncology, Kyowa, Lilly, Loxo, Lysarc, Lytix Biopharma, MedImmune, Menarini, Merus, MSD, Nanobiotix, Nektar Therapeutics, Novartis, Octimet, Oncoethix, Oncopeptides AB, Orion, Pfizer, PharmaMar, Pierre Fabre, Roche, Sanofi, Servier, Sierra Oncology, Taiho, Takeda, Tesaro and Xencor. J.B.M. reports personal fees from AbbVie, Jazz PHARMA and Astellas. S.M. reports personal fees from statistical advice to IDDI, Janssen Cilag and Amaris and from data and safety monitoring membership of clinical trials (Hexal, Steba, IQVIA, Roche, Sensorion, Biophytis, Servier and Yuhan). A.A. reports grant support, paid to her institution, from F. Hoffmann-La Roche. F.B. reports personal financial interests with AstraZeneca, Bayer, Bristol Myers Squibb, Boehringer Ingelheim, Eli Lilly Oncology, F. Hoffmann–La Roche Ltd, Novartis, Merck, Mirati, MSD, Pierre Fabre, Pfizer, Seattle Genetics and Takeda; institutional financial interests with AbbVie, ACEA, Amgen, AstraZeneca, Bayer, Bristol Myers Squibb, Boehringer Ingelheim, Eisai, Eli Lilly Oncology, F. Hoffmann–La Roche Ltd, Genentech, Ipsen, Ignyta, Innate Pharma, Loxo, Novartis, MedImmune, Merck, MSD, Pierre Fabre, Pfizer, Sanofi-Aventis and Takeda and non-financial interests (as a principal investigator) for AstraZeneca, BMS, Merck, Pierre Fabre and F. Hoffmann-La Roche, Ltd–sponsored trials (or ISR). J.B. reports honoraria from Bristol Myers Squibb; a consulting or advisory role for Bristol Myers Squibb, MSD, PharmaMar (Inst), Bristol Myers Squibb (Inst) and Merck Serono (Inst) and travel and accommodation expenses from Bristol Myers Squibb. Other authors report no conflict of interest. Y. Takahashi declares no conflict of interest. Her editorial work for the present article has been funded by Inserm., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)