Onxeo

Pre-Annual General Meeting Information • May 21, 2021

Onxeo's Combined General Meeting on June 10, 2021 in camera: availability of preparatory documents and live webcast login information

Paris (France), May 21, 2021 - 5:45 p.m. CEST - Onxeo S.A. (Euronext Paris, NASDAQ Copenhagen: ONXEO - FR0010095596), ("Onxeo", "the Company" or "the Group"), a clinical-stage biotechnology company specializing in the development of innovative drugs targeting tumor DNA Damage response (DDR) in oncology, in particular against rare or resistant cancers, announces today the availability of the preparatory documents for its Combined General Meeting of June 10, 2021 and specifies the live webcast login information.

In the context of the Covid-19 pandemic, the Combined General Meeting on June 10, 2021 at 03:00 p.m., will be held in camera, without the presence of shareholders or other persons usually eligible to attend.

The General Meeting will be webcasted live (in French) via a web conferencing system and shareholders of Onxeo are invited to login through the following link:

https://us02web.zoom.us/webinar/register/WN\_GkVbNWV8RhutMoH7cekSyw

• This link allows shareholdersto pre-register for the General Meeting by indicating your name, first name and e-mail. They will then receive a confirmation of their registration with the possibility to add the event to their agenda.
• On June 10, 2021, the shareholders will be able to log on to this same link. The Meeting will start at 03:00 pm sharp and they will be able to follow the presentation commented by the management of Onxeo and the course of the Meeting directly on their computer.
• At any time during the presentation, they will be able to send their questions via the web platform. Questions will be answered during the Q&A session*.

In accordance with current regulations and the recent recommendations of the French stock-market authority (AMF), Onxeo shareholders are requested to cast their votes exclusively through mail or online voting prior to the General Meeting:

• online voting is available and must be used as a priority: the secure voting platforms VOTACCESS in France and Computershare in Denmark will be active on May 21, 2021 at 9 a.m.;
• alternatively, shareholders can also vote by postal ballot, in accordance with the terms and conditions indicated in the prior notice published in the BALO on May 5, 2021.

All documents relating to this General Meeting are available on the company's website, in the General Meetings section.

The Meeting will be chaired by Mrs Danièle Guyot-Caparros as Chairman of the Board of Directors. Mr. Nicolas Fellmann, Chief Financial Officer of the Company, will act as Secretary of the Bureau. In accordance with the terms of Article 8 of Decree dated December 18, 2020, Financière de la Montagne, represented by Mr. Nicolas Trebouta, and Invus Public Equities LP, represented by Mr. Julien Miara, have been appointed scrutineers and have agreed to perform these duties.

If you have any questions about voting procedures, please contact the Investor Relations team by e-mail at ag2021@onxeo.com.

^* Please note that, given the impossibility of verifying the shareholder status of participants in the video transmission, the Q&A session is informal and has no legal value within the meaning of Article L 225-108 of the French Commercial Code. The procedures for written questions from shareholders within the meaning of the regulations are detailed in the notice of meeting published in the BALO and the JAL on May 21, 2021 and available on the Company's website.

About Onxeo

Onxeo (Euronext Growth Paris: ALONX, Nasdaq First North Copenhagen: ONXEO) is a clinical-stage biotechnology company developing innovative oncology drugs targeting tumor DNA-binding functions through unique mechanisms of action in the sought-after field of DNA Damage Response (DDR). The Company is focused on bringing early-stage first-in-class or disruptive compounds from translational research to clinical proof-of-concept, a value-creating inflection point appealing to potential partners.

platON™ is Onxeo's proprietary chemistry platform of oligonucleotides acting as decoy agonists, which generates new innovative compounds and broaden the Company's product pipeline.

AsiDNA™, the first compound from platON™, is a first-in-class, highly differentiated DNA Damage Response (DDR) inhibitor based on a decoy and agonist mechanism acting upstream of multiple DDR pathways. Translational research has highlighted the distinctive properties of AsiDNA™, notably its ability to abrogate tumor resistance to PARP inhibitors regardless of the genetic mutation status. AsiDNA™ has also shown a strong synergy with other tumor DNAdamaging agents such as chemotherapy and PARP inhibitors. The DRIIV-1 (DNA Repair Inhibitor-administered IntraVenously) phase I study has evaluated AsiDNA™ by systemic administration (IV) in advanced solid tumors and confirmed the active doses as well as a favorable human safety profile. The ongoing DRIIV-1b extension study is evaluating the safety and efficacy of AsiDNA™ at a dose of 600 mg in combination with the reference chemotherapy, carboplatin -/+ paclitaxel, in advanced metastatic tumors. Preliminary results from both cohorts showed good tolerability, stabilization of the disease and an increase in treatment duration compared to previous treatments. The ongoing REVOCAN phase 1b/2 study evaluates the effect of AsiDNA™ on the acquired resistance to PARP inhibitor niraparib in relapsed ovarian cancer (sponsored by Gustave Roussy). A phase 1b/2 study, AsiDNA™ Children, will be initiated in 2021 to evaluate the association of AsiDNA™ with radiotherapy in children with relapsed high-grade glioma (sponsored by Institut Curie).

OX401 is a new drug candidate from platON™, optimized to be a next-generation PARP inhibitor acting on both the DNA Damage Response and the activation of immune response, without inducing resistance. OX401 is undergoing preclinical proof-of-concept studies, alone and in combination with immunotherapies.

For further information, please visit www.onxeo.com.

Forward looking statements

This communication expressly or implicitly contains certain forward-looking statements concerning Onxeo and its business. Such statements involve certain known and unknown risks, uncertainties and other factors, which could cause the actual results, financial condition, performance or achievements of Onxeo to be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements. Onxeo is providing this communication as of this date and does not undertake to update any forward-looking statements contained herein as a result of new information, future events or otherwise. For a discussion of risks and uncertainties which could cause actual results, financial condition, performance or achievements of Onxeo to differ from those contained in the forward-looking statements, please refer to the risk factors described in the most recent Company's registration document or in any other periodic financial report and in any other press release, which are available free of charge on the websites of the Company Group (www.onxeo.com) and/or the AMF (www.amf-france.org).

Contacts

Onxeo

Valerie Leroy, Investor Relations investors@onxeo.com +33 1 45 58 76 00

Media Relations Nicolas Merigeau NewCap onxeo@newcap.eu +33 1 44 71 94 98

Investor Relations / Strategic Communication Dušan Orešanský / Emmanuel Huynh NewCap onxeo@newcap.eu +33 1 44 71 94 92