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Treatment for Acute Lymphoblastic Leukemia

FDA Begins Priority Review of ILEX NDA for Clofarabine in Pediatric Acute Leukemia; Filing Acceptance Indicates Start of Official Review Period

SAN ANTONIO, June 3, 2004--ILEX(tm) Oncology Inc. (Nasdaq:ILXO) announced today that the U.S. Food and Drug Administration (FDA) has accepted the filing of its New Drug Application (NDA 21-673) for clofarabine for the treatment of refractory or relapsed acute leukemia in children. The NDA has been granted a priority review by the FDA. Clofarabine received fast-track designation in 2003. If approved, clofarabine will become the Company's second marketed product.

"We are very pleased with the FDA's decision to accept the clofarabine filing and we will work closely with the agency during this critical period," said ILEX CEO and President Jeff Buchalter.

On March 29, 2004, ILEX completed a "rolling" NDA submission for clofarabine. The application seeks marketing approval for clofarabine in refractory or relapsed acute pediatric leukemias.

Historically, cancer drugs are approved and made available for adults first and then modified for children. If approved by the FDA, clofarabine would be the first drug to be labeled for pediatric leukemia exclusively in more than a decade. Cure rates for pediatric leukemia have improved dramatically over the past several decades. However, children who do not respond to initial therapy have a very poor prognosis and long-term remissions are rare.

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
Founded in 1994 as an oncology drug development company, ILEX has a marketed product, CAMPATH(R) in the United States and MABCAMPATH(R) in the European Union, and is advancing an innovative and diversified pipeline of compounds focused on the treatment of cancer. The ILEX pipeline comprises product candidates at various stages of clinical development, including monoclonal antibodies, novel cytotoxic agents, angiogenesis inhibitors and signal transduction inhibitors. Based in San Antonio, Texas, ILEX maintains a core competency in oncology drug development. ILEX also conducts research in angiogenesis inhibition, cell signaling, medicinal chemistry and nuclear receptor biology at its laboratories in Boston, Mass., and Geneva, Switzerland. In February 2004, ILEX announced its agreement to merge with Genzyme Corporation, a global biotechnology company. The merger, subject to ILEX stockholder approval and other customary conditions, is expected to close in mid-2004.

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: June 2004

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