December 5, 2003

News Release: Bioenvision Announces New Breast Cancer Studies with Modrenalby a New, Proprietary, Method Improves Therapeutic Effectiveness in Human Breast Cancer Model

Bioenvision, Inc. (Amex:BIV) today announced its intention to conduct new studies in the U.K. in pre-menopausal, pre-operative and post-menopausal women for its lead breast cancer treatment Modrenal(R) (trilostane).

The announcement was made at the prestigious International Breast Cancer Symposium in San Antonio, Texas, where key consultations are taking place with leading breast cancer specialists to finalize protocols for the new studies. The aim of the post-menopausal Phase IV study is to confirm Modrenal's proven clinical benefit in patients who have relapsed after third generation aromatase inhibitor therapy. Sixty patients will be enrolled into the study, completion of which is planned for fourth quarter 2004.

The Phase II study of pre-menopausal breast cancer patients will evaluate Modrenal's efficacy following relapse to first line endocrine therapy. Fifty-five patients will be enrolled in this study, which is expected to be completed by the end of 2004.

The research, planned to commence in the first quarter of 2004, will build upon the existing large database and further evaluate the efficacy of Modrenal in women with breast cancer who may fall outside the current U.K. indication for the treatment of advanced, post-menopausal breast cancer following relapse on prior endocrine therapy.

Leading U.K. Cancer Specialist, Professor Robert Leonard of The South Wales Cancer Institute, Swansea, present in San Antonio commented, 'Modrenal has shown impressive clinical benefit rates in patients with previously treated breast cancers. The new studies will help to ensure that the full potential of Modrenal, as part of a fully integrated treatment programme, can be determined for wider patient groups such as pre-menopausal women and those who have been diagnosed with breast cancer and are awaiting surgery.'

Modrenal is licensed in Europe and marketed by Bioenvision for the treatment of advanced post-menopausal breast cancer.

Modrenal has been thrust into the spotlight further by the recent discovery of two novel mechanisms of action, which are helping physicians to explain the high clinical benefit rates reported for the drug.

The first discovery, by a team led by Professor Gavin Vinson at Queen Mary, University of London and published in the International Journal of Cancer in 2002(1), explained how Modrenal can uniquely change the effect of the hormone estrogen at a binding site now known to be important in the proliferation of breast cancer - estrogen receptor beta. The effect is to reverse or slow the progression of breast cancer.

Additional research presented for the first time at the Nottingham International Breast Cancer Conference in September 2003, also outlined the ability of Modrenal to block the action of estrogen through a mechanism involving an important protein, AP1, providing an additional means to reverse or reduce the rate of cancer cell proliferation.

Dr. Christopher B. Wood, Chairman and CEO of Bioenvision, commented, 'Our new understanding of the mechanism of action has helped physicians recognize how Modrenal could benefit an even larger number of patients with breast cancer. We look forward to commencing the new research studies to ensure that Modrenal can become available to all who need it.'

To confirm the scientific data in the clinical setting, a Phase II study of Modrenal also has been designed to assess the changes in biological indices. Modrenal will be given in the neo-adjuvant setting three weeks prior to surgery for breast cancer. Key markers of cell proliferation and apoptosis will be measured on biopsy samples taken pre- and post Modrenal therapy.

1. Puddefoot JR et al 'Non-Competitive Steroid Inhibition of Oestrogen Receptor Functions'. Int J Cancer: 101, 17-22 (2002)

About Modrenal

Modrenal has been approved for the treatment of advanced post-menopausal breast cancer by United Kingdom regulatory authorities. It has been extensively studied in controlled trials in the United States, Europe and Australia. Over 700 patients with breast cancer have received Modrenal in clinical trials, and its anti-tumor activity has been well documented; it is effective in a significant proportion of breast cancer patients, particularly those with hormone-sensitive tumors.

About Bioenvision

Bioenvision (Amex:BIV), a New York based biopharmaceutical company, primarily focuses on 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 approval for marketing in the United Kingdom for the treatment of advanced 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.

SOURCE: Bioenvision, Inc.

Bioenvision Ltd Media: Executive Director Hugh S Griffith, +44 (0) 131 248 3555 This email address is being protected from spambots. You need JavaScript enabled to view it. or Investors: Director of Finance, General Counsel David P. Luci, 212-750-6700 This email address is being protected from spambots. You need JavaScript enabled to view it.

WEBSITE EMAIL