Prospectus posted and EGM date announced for Antisoma's acquisition of Xanthus Pharmaceuticals and related fundraising

NOT FOR DISTRIBUTION, PUBLICATION OR RELEASE IN OR INTO THE UNITED STATES OR CANADA London, UK: 19 May 2008: Cancer-focused biotechnology company Antisoma plc (LSE: ASM; US OTC: ATSMY) announced on 16 May 2008 that it has entered into an agreement to acquire private US oncology company Xanthus Pharmaceuticals, Inc. in an all-share deal valued at GBP 26.8 million (USD 52.2 million). Simultaneously, Antisoma has executed a fundraising that will provide an additional GBP 20.9 million before expenses to the Enlarged Group. The acquisition of Xanthus and, as a consequence, the associated fundraising are conditional on approval of the acquisition by Antisoma's shareholders at an EGM to be held on 9 June 2008. The Antisoma Board recommends that shareholders support the acquisition and fundraising. A prospectus relating to the acquisition and fundraising and containing a Notice of EGM was sent to shareholders on 16 May 2008. Copies are also available for viewing at Antisoma's offices, situated at Chiswick Park Building 5, 566 Chiswick High Road, London W4 5YF and at the offices of Piper Jaffray situated at One South Place, London EC2M 2RB. Note regarding release on Friday 16 May: An error in the transmission of the release on 16 May 2008 entitled "Antisoma to acquire Boston-based Xanthus Pharmaceuticals" resulted in the inadvertent deletion of the following paragraph: The fundraising element of the transaction comprises a placing of 51.9 million new ordinary shares in the Company to new and existing investors in Antisoma (the "Placing") and a subscription of 28.5 million new ordinary shares in Antisoma by existing investors in Xanthus at a price of 26.0p, representing a discount of 5.5% to the closing middle-market price of an Antisoma ordinary share on the day before this announcement. The new shares to be issued in the fundraising represent 18.0% of the number of issued Antisoma ordinary shares before this announcement. The Placing is fully underwritten by Piper Jaffray, which also advised Antisoma on the transaction. It is anticipated that these new ordinary shares, which will rank pari-passu with existing ordinary shares, will commence dealing on or around 10th June 2008. Enquiries: Daniel Elger, Director of Communications +44 7909 915068 Antisoma plc Lisa Baderoon, Mark Court, Rebecca Skye Dietrich +44 (0)20 7466 5000 Buchanan Communications Neil Mackison +44 (0)20 3142 8700 Rupert Winckler Piper Jaffray This document does not constitute an offer or invitation to purchase or subscribe for any securities of Antisoma and no part of it shall form the basis of or be relied upon in connection with any contract or commitment whatsoever. The information contained herein is not for publication, distribution or release in or into the United States. The material set forth herein is for informational purposes only and is not intended, and should not be construed, as an offer of securities for sale in the United States. The securities described herein have not been and will not be registered under the U.S. Securities Act of 1933, as amended (the "Securities Act"), or the laws of any state or other jurisdiction, and may not be offered or sold within the United States, except pursuant to an exemption from, or in a transaction not subject to, the registration requirements of the Securities Act and applicable laws of any state or other jurisdiction. There is no intention to register any portion of the securities described herein in the United States. This document is not an offer to sell or the solicitation of an offer to buy any securities in any jurisdiction where such offer or sale is not permitted. Certain matters discussed in this statement are forward looking statements that are subject to a number of risks and uncertainties that could cause actual results to differ materially from results, performance or achievements expressed or implied by such statements. These risks and uncertainties may be associated with product discovery and development or licensing activities, including statements regarding the clinical development programmes, the expected timing of clinical trials and regulatory filings, out-licensing opportunities, and funding requirements. Such statements are based on management's current expectations, but actual results may differ materially. ---END OF MESSAGE--- ---END OF MESSAGE---