Onxeo

Report Publication Announcement • May 12, 2015

Publication of a Letter to Shareholders – May 2015

Paris (France), Copenhagen (Denmark), May 12, 2015 – Onxeo S.A. (Euronext Paris, NASDAQ Copenhagen: ONXEO), an innovative company specializing in the development of orphan oncology drugs, today announces the publication of the Letter to Shareholders - May 2015.

The Shareholders Letter is available on the website at: www.onxeo.com (Media or Investors/Shareholders).

About Onxeo

Onxeo has the vision to become a global leader and pioneer in oncology, with a focus on orphan or rare cancers, through developing innovative therapeutic alternatives designed to "make the difference". The Onxeo team is determined to develop innovative medicines that provide patients with hope and significantly improve their lives.

Key orphan oncology products at the advanced development stage are:

Livatag® (Doxorubicin Transdrug™): Phase III in hepatocellular carcinoma Validive® (Clonidine Lauriad® ): Phase II in severe oral mucositis: Positive preliminary top-line results Beleodaq® (belinostat): registered in the US in peripheral T-cell lymphoma For more information, visit the website www.onxeo.com

Disclaimer

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 ("Facteurs de Risque") section of the 2014 Reference Document filed with the AMF on April 14, 2015, which is available on the AMF website (http://www.amf-france.org) or on the company's website (www.onxeo.com).

Contacts :

Judith Greciet, CEO j.greciet@onxeo.com Nicolas Fellmann, CFO n.fellmann@onxeo.com +33 1 45 58 76 00

Caroline Carmagnol onxeo@alizerp.com +33 6 64 18 99 59 / +33 1 44 54 36 61