Positive Data on Bioenvision's Clofarabine Published in Blood, the Journal of the American Hematology Society.

Business Editors/Health/Medical Writers

NEW YORK--(BUSINESS WIRE)--Oct. 29, 2003

Bioenvision, Inc. (Amex:BIV) today announced that positive data on its lead anti-cancer drug, clofarabine, has been published in Blood, the journal of the American Hematology Society. In the Phase I study, clofarabine showed a 32% response rate in pediatric patients with advanced leukemia (Jeha S et al, Blood First Edition Paper available online, to be published in the upcoming months; DOI 10.1182/blood-2003-06-2122). The article is available online at www.bloodjournal.org. Clofarabine is currently in Phase II trials for pediatric leukemia in the United States.

The study enrolled 25 children with acute myelogenous leukemia (AML) and acute lymphocytic leukemia (ALL), all of whom were in salvage status, having failed previous therapy, and had a very poor prognosis. These patients had failed a median of three prior chemotherapy regimens and over one third had relapsed after receiving a bone marrow transplant. The results showed clofarabine had significant activity in this poor prognosis patient population. Eight (32%) patients responded to clofarabine, with 5 of these patients (20%) having a complete response (CR). The responses achieved with clofarabine were also durable, with four (80%) of the complete responses lasting over one year.

Four other patients had a reduction in their leukemic cell count that was sufficient to allow them to go on to receive bone marrow transplants. When these patients were included in the analysis the total objective response rate increased to 48%. Side effects of clofarabine were reasonably well tolerated and considered manageable by the investigators.

Commenting on the results, lead investigator, Dr. Sima Jeha, MD of St Jude Children's Research Hospital, said, "We are encouraged that the results showed that clofarabine was safe and had significant activity in this poor prognosis patient population."

The study authors concluded that "clofarabine is the first deoxyadenosine analog with promising activity in pediatric ALL, pediatric AML and adult acute leukaemia at doses that are well tolerated."

"We are pleased to have the results of this pediatric study published in a peer reviewed journal of Blood's stature," said Hugh S. Griffith, Commercial Director of Bioenvision. "Clofarabine has demonstrated significant activity in children with leukemia who are refractory to other therapies and have very limited options. We are very encouraged by these data and look forward to the conclusion of the Phase II studies in pediatric leukemia which are ongoing at leading cancer centers throughout the U.S."

About Clofarabine

Clofarabine is a next-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).

Bioenvision granted ILEX Oncology, Inc. (Nasdaq:ILXO) 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.

About Bioenvision

Bioenvision's (Amex:BIV) primary focus is 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; 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.