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Treatment for Acute Lymphoblastic Leukemia

ILEX Updates Clofarabine NDA with Encouraging Results; Additional Patient Data Resets FDA Action Date

SAN ANTONIO, August 24, 2004 - ILEX Oncology Inc. (Nasdaq:ILXO) announced today that it has chosen to provide the U.S. Food and Drug Administration (FDA) with new patient data to support the New Drug Application (NDA) it submitted for clofarabine for the treatment of refractory or relapsed acute leukemia in children. The decision to update the filing was based on encouraging efficacy results from a cohort of additional patients. Based on the significant new data added to the original filing, the FDA has reset the Prescription Drug User Fee Act (PDUFA) response date to December 30, 2004.

"ILEX chose to submit these results so the FDA could assess a larger body of data," said ILEX Chief Medical Officer and pediatric oncologist, Steve Weitman, M.D. "We continue to be encouraged by clofarabine's activity in this group of patients who have relapsed or are refractory to available treatments."

The NDA filing was based on data from 70 pediatric patients enrolled in two pivotal Phase II acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) trials. The update is based on data from 14 additional patients, bringing the total number of patients included in the filing to 84. Of the new cohort, four of nine ALL patients and two of five AML patients responded to clofarabine.

The total ALL group (n=49) achieved a 31 percent overall response rate, with six complete remissions (CR), four complete marrow remissions in the absence of platelet recovery (CRp) and five partial remissions (PR). The total AML group (n=35) achieved a 26 percent response rate, with one CRp and eight PRs. An interim monitoring of these AML patients showed that seven of the nine responders went on to receive transplants following their responses to clofarabine, which provides an opportunity to prolong life for these patients.

Clofarabine was previously granted orphan drug designation for the treatment of adult and pediatric ALL and AML by the FDA. In the U.S., orphan drug status provides for seven years of market exclusivity for the orphan drug indication following the FDA's marketing approval. The FDA also recently granted six months of extended market exclusivity to clofarabine under the Best Pharmaceuticals for Children Act. If approved by the FDA, clofarabine would be the first drug to be labeled initially for pediatric leukemia in more than a decade.

About Clofarabine
Clofarabine is a next generation of the drug class purine nucleoside analogs which all inhibit DNA production necessary for cancer cell growth. Bioenvision, Inc. (NASDAQ: BIVN) sub-licensed ILEX the right to develop and market clofarabine for human cancer indications 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. As is its exclusive right, Bioenvision is developing clofarabine in the rest of the world. Bioenvision originally obtained clofarabine development and commercialization rights under patents held by Southern Research Institute.

About ILEX
ILEX Oncology Inc. is an oncology drug development company with a marketed product, CAMPATH(R) in the United States and MABCAMPATH(R) in the European Union, as well as a pipeline of investigational compounds focused on the treatment of cancer. ILEX maintains a core competency in oncology drug development in San Antonio, Texas. ILEX also conducts research in angiogenesis inhibition, cell signaling, medical chemistry and nuclear receptor biology at its laboratories. In February 2004, ILEX entered into an agreement and plan of merger with Genzyme(R) Corporation, a leading global biotechnology company. The merger is expected to close this summer, but remains subject to clearance by the Federal Trade Commission and other customary closing conditions.
Further information about ILEX can be found on the company's Web site at

About Bioenvision, Inc.
Bioenvision's (NASDAQ:BIVN) primary focus is the 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); and other products in clinical trials. Bioenvision also is developing anti-infective technologies, including the OLIGON technology, an advanced biomaterial that has been approved for certain indications by the FDA in the U.S., and is being sold by a co-development partner of Bioenvision.

Posted: August 2004

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