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Treatment for Acute Lymphoblastic Leukemia

FDA Will Grant ILEX's Clofarabine Additional Six-Month Pediatric Exclusivity; Incentive Provides Extended Patent Protection Upon Marketing Approval

SAN ANTONIO, Jul 21, 2004 - ILEX(TM) Oncology Inc. (Nasdaq:ILXO) announced today that the U.S. Food and Drug Administration (FDA) will grant six months of extended market exclusivity to clofarabine under the Best Pharmaceuticals for Children Act. Clofarabine is currently under priority review by the FDA for the treatment of refractory or relapsed acute leukemia in children. If approved by the FDA, clofarabine would be the first drug to be labeled initially for pediatric leukemia in more than a decade.

"This is an important milestone for children with cancer and for the FDA because children are usually an afterthought in oncology drug development," said Children's Cause for Advocacy President, Susan L. Weiner, Ph.D. "Hopefully this good news will set a precedent for other companies to make children with cancer a priority in their drug development plans."

The Best Pharmaceuticals for Children Act offers extended market exclusivity to drug developers as an incentive to increase therapeutic research in children.

Clofarabine was previously granted orphan drug designation for the treatment of adult and pediatric acute lymphoblastic leukemia and acute myeloid leukemia. In the United States, orphan drug status provides for seven years of market exclusivity for the orphan drug indication following the FDA's marketing approval.

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. (AMEX:BIV) 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 Boston, Mass., and Geneva, Switzerland. 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 (AMEX:BIV) 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 United States, and is being sold by a co-development partner of Bioenvision.

Posted: July 2004

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