Bioenvision's Clofarabine Shows Promising Activity in Children with Acute Lymphoblastic Leukemia.

Business Editors

SAN DIEGO--(BUSINESS WIRE)--Dec. 9, 2003

Results Presented at Annual Meeting of American Society of Hematology

Bioenvision, Inc. (Amex:BIV) today announced that interim results from a multi-center Phase II study with clofarabine in heavily pretreated children with acute lymphoblastic leukemia (ALL) continue to show promising activity. For the first time, duration of response has also been reported. These data were presented at the American Society of Hematology 45th Annual Meeting and Exposition in San Diego. The Phase II study was conducted by Bioenvision's North American co-development partner, Ilex Oncology Inc. (Nasdaq:ILXO).

A 25 percent overall response rate was achieved in the 36 patients presented, with three complete remissions (CR), three complete marrow remissions in the absence of platelet recovery (CRp) and three partial remissions (PR). Five of the nine children who responded to clofarabine treatment were able to receive a transplant.

Patients enrolled in this study had failed a median of three treatment regimens prior to receiving clofarabine. In addition, 20% of patients had also received a prior bone marrow transplant. This Phase II multi-center study is ongoing and has been expanded to enrol 60 patients.

"We are very excited about these data because, despite the poor prognosis heavily pretreated children face, several patients are achieving durable responses," said Sima Jeha, M.D., Director, Developmental Therapeutics, Division of Leukemia/Lymphoma, St. Jude Children's Research Hospital.

About Clofarabine

Bioenvision's partner in North America, ILEX Oncology Inc. (Nasdaq:ILXO), has submitted the first part of a New Drug Application (NDA) with the U.S. Food and Drug Administration (FDA) for clofarabine for the treatment of refractory or relapsed pediatric acute leukaemia. It is anticipated that the remainder of the NDA will be submitted on a "rolling" basis and is expected to be completed in the first half of 2004.

Bioenvision granted ILEX the right to develop clofarabine in the United States and Canada. Bioenvision is entitled to milestone payments tied to the development of the compound and is entitled to royalties on North American sales. Bioenvision is developing clofarabine exclusively in the rest of the world. Bioenvision originally obtained clofarabine development and commercialization rights under patents held by Southern Research Institute.

Clofarabine is a second-generation purine nucleoside antimetabolite. Nucleoside analogues are antimetabolites that affect DNA synthesis. Clofarabine was rationally designed to combine many of the favorable properties of the two most commonly used nucleoside analogs, fludarabine and cladribine, but is reported to have greater potency at damaging the DNA of Leukemia cells than these other agents. (Blood, "Mitochondrial Toxicity of Deoxyadenoside Analogs", November 15, 2000, Volume 96, Number 10). In a single center Phase II study of clofarabine in patients with refractory AML, 42% of the patients had a complete response rate (CR) and a further 13% had a partial response (CRp).

About Bioenvision

Bioenvision (Amex:BIV), a New York based biopharmaceutical company, is primarily focused on the acquisition, development and distribution of compounds and technologies for the treatment of cancer. Bioenvision has a broad pipeline of products for the treatment of cancer, including: clofarabine (in co-development with ILEX Oncology, Inc.), Modrenal(R) (for which Bioenvision has obtained regulatory approval for marketing in the United Kingdom for the treatment of post-menopausal breast cancer following relapse to initial hormone therapy), and other products in clinical trials. Bioenvision is also developing anti-infective technologies, including the OLIGON technology; an advanced biomaterial that has been incorporated into various FDA approved medical devices. For more information on Bioenvision please visit our Web site at www.bioenvision.com.

Certain statements contained herein are "forward-looking" statements (as such term is defined in the Private Securities Litigation Reform Act of 1995). Because these statements include risks and uncertainties, actual results may differ materially from those expressed or implied by such forward-looking statements. Specifically, factors that could cause actual results to differ materially from those expressed or implied by such forward-looking statements include, but are not limited to: risks associated with preclinical and clinical developments in the biopharmaceutical industry in general and in Bioenvision's compounds under development in particular; the potential failure of Bioenvision's compounds under development to prove safe and effective for treatment of disease; uncertainties inherent in the early stage of Bioenvision's compounds under development; failure to successfully implement or complete clinical trials; failure to receive marketing clearance from regulatory agencies for our compounds under development; acquisitions, divestitures, mergers, licenses or strategic initiatives that change Bioenvision's business, structure or projections; the development of competing products; uncertainties related to Bioenvision's dependence on third parties and partners; and those risks described in Bioenvision's filings with the SEC. Bioenvision disclaims any obligation to update these forward-looking statements.