Bioenvision's Modrenal -Trilostane- Effective Against Advanced Endocrine Resistant Breast Cancer.

Business Editors/Health/Medical Writers

NEW YORK--(BUSINESS WIRE)--June 7, 2004

Clinical Data and Mechanistic Study on Drug's Effect

on Signal Transduction Pathways Presented at

40th Annual Meeting Of American Society Of Clinical Oncology 

Bioenvision, Inc. (AMEX:BIV) today announced that data on its drug Modrenal(R) (trilostane) were presented at the 40th Annual Meeting of the American Society of Clinical Oncology in New Orleans. Presentations included results of a systematic clinical data analysis of Modrenal in post-menopausal breast cancer patients and data on the drug's mechanism of action. Both presentations suggest the drug is active against breast tumors with acquired endocrine resistance.

The systematic analysis, presented by a consortium of investigators in the UK and the MD Anderson Cancer Center in Houston, TX, included over 700 post-menopausal women with assessable progressing advanced breast cancer were treated with Modrenal in multiple centers across eleven countries. All patients had received prior endocrine and/or chemotherapy. Endocrine resistant patients who received Modrenal for greater than 12 weeks achieved an objective response of 36% and an overall clinical benefit rate of 55%.

An additional study examining Modrenal's mechanism of action, presented by Dr. Gavin Vinson's group at the University of London, compared directly the effect of Modrenal versus tamoxifen on signal transduction pathways known to promote breast cancer cell survival and resistance to traditional anti-cancer agents. Specifically, the study looked at the effect of both drugs on Activating protein-1 (AP1) and progesterone receptor mediated signalling. Both molecules are involved with signalling mechanisms associated with a variety of tumorigenic processes, including cell proliferation and growth factor mediated cell survival. The data showed that Modrenal effectively repressed AP1 signalling in breast cancer cells in the presence of estrogen, while tamoxifen did not. Additionally, the research demonstrated that Modrenal effectively repressed progesterone receptor-mediated signalling while tamoxifen in fact augmented this signalling.

Commenting on the results, Professor Vinson said, "Taken together, the mechanistic data point to Modrenal as a drug with a unique profile of action, and help explain the proven benefit to breast cancer patients who have become refractory to tamoxifen therapy, as seen in the systematic analysis."

About Bioenvision

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 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.