Onxeo

Report Publication Announcement • Apr 25, 2018

Publication of 2017 Registration Document

Paris, April 25, 2018 – 6:30 pm CEST – Onxeo S.A. (Euronext Paris, NASDAQ Copenhagen: ONXEO FR0010095596), a biotechnology company specializing in the development of innovative drugs in oncology, in particular against rare or resistant cancers, today announced the publication of the Company's 2017 Registration Document.

The 2016 Registration Document, filed with the French Market Authorities (Autorité des Marchés Financiers) on April 25, 2018, is available to the public free of charge upon request, as per current legal regulations, at on the Company's website: http://www.onxeo.com/en/investisseurs/resultats-et-publications.

Copies of the Registration Document are also available at the head offices of Onxeo – 49 Boulevard du Général Martial Valin, 75015.

The annual financial report, the report on corporate governance, as well as the auditors' reports and information on the fees paid to the statutory auditors in 2017 are included in this Registration Document

About Onxeo

Onxeo (Euronext Paris, NASDAQ Copenhagen: ONXEO) is a French biotechnology company developing innovative oncology drugs based on DNA-targeting and epigenetics, two of the most sought-after mechanisms of action in cancer treatment today. The Company is focused on bringing early-stage first-in-class or disruptive compounds (proprietary, acquired or in-licensed) from translational research to clinical proof-of-concept, a value-creating inflection point appealing to potential partners.

Onxeo's R&D pipeline includes belinostat, an HDAC inhibitor (epigenetics) currently being developed in oral form to be used in combination with other anti-cancer agents for liquid or solid tumors. Belinostat is already conditionally FDA-approved in the US as a 2 nd line treatment for patients with peripheral T cell lymphoma and marketed in the US by Onxeo's partner, Spectrum Pharmaceuticals, under the name Beleodaq® (belinostat IV form).

Onxeo is also developing AsiDNA™, a first-in-class DNA break repair inhibitor based on a unique decoy mechanism. AsiDNA™ has already successfully completed a Phase I trial in metastatic melanoma via local administration, and is currently being developed for systemic (IV) administration in solid tumors.

AsiDNA™ is the first compound generated from platON™, the Company's proprietary chemistry platform of decoy oligonucleotides based on three components, a sequence of double strand oligonucleotides, a linker and a cellular uptake facilitator. PlatON™ will continue to generate new compounds that will broaden Onxeo's pipeline.

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 section 5.5.1.4 "Risk Factors" ("Facteurs de Risque") of the 2016 reference document filed with the Autorité des marchés financiers on April 24, 2017 under number D.17-0423, which is available on the Autorité des marchés financiers website (www.amf-france.org) or on the Company's website (www.onxeo.com).

Onxeo Media Relations Caroline Carmagnol / Tatiana Vieira Investor Relations / Strategic Communication

PRESS RELEASE

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

alize-onxeo@alizerp.com 33 (0) 1 44 54 36 65

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

Investor Relations US Brian Ritchie LifeSci Advisors britchie@lifesciadvisors.com +1 212 915 2578