PRAECIS PHARMACEUTICALS INCORPORATED Study Results Published at the American Society of Clinical Oncology Annual Meeting.

Business Editors/Health/Medical Writers

WALTHAM, Mass.--(BUSINESS WIRE)--May 31, 2003

PRAECIS PHARMACEUTICALS INCORPORATED (NASDAQ: PRCS) today announced that results from its clinical study of Plenaxis(TM) (abarelix for injectable suspension) in the treatment of advanced, symptomatic prostate cancer were published in the 39th Annual American Society of Clinical Oncology (ASCO) "Meeting Proceedings." The Company previously reported results from this clinical study in February 2003. The two abstracts published today include data relating to the avoidance of surgical castration and reduction in pain and the use of pain medication, as well as 48-week follow-up data not previously reported relating to the anti-cancer response rates seen in advanced, symptomatic prostate cancer patients treated with the Company's investigational therapy, Plenaxis(TM).

"The data presented today demonstrates how the novel mechanism of action of Plenaxis(TM), a GnRH antagonist, can work to improve the clinical symptomatology in advanced prostate cancer patients," stated William K. Heiden, PRAECIS' President and Chief Operating Officer. "If approved, Plenaxis(TM) could provide an important treatment alternative for certain advanced prostate cancer patients who today have limited therapeutic options."

Prostate cancer grows under the influence of the male hormone, testosterone. The goal of treatment is to reduce testosterone rapidly. Today, many advanced, symptomatic prostate cancer patients are destined for bilateral orchiectomy (surgical castration) due to the perceived risks associated with currently available hormonal therapies, known as LHRH agonists. These therapies induce an initial testosterone surge and may result in worsening symptoms. In contrast, GnRH antagonists have been shown to rapidly reduce testosterone levels while avoiding the initial testosterone surge characteristic of LHRH agonists.

The Company resubmitted its New Drug Application (NDA) for Plenaxis(TM) to the United States Food and Drug Administration (FDA) on February 27, 2003. The Company is seeking approval to market Plenaxis(TM) in the United States for use in a defined sub-population of advanced prostate cancer patients for whom the use of existing hormonal therapies may not be appropriate. The Company expects to receive a response from the FDA regarding the approvability of its NDA by August 27, 2003.

PRAECIS PHARMACEUTICALS INCORPORATED is a biotechnology company focused on the discovery and development of pharmaceutical products using its proprietary LEAP(TM) (Ligand Evolution to Active Pharmaceuticals) technology. LEAP(TM) combines the power of biological selection with the advantages of medicinal chemistry in a unique molecular evolution process. PRAECIS employed LEAP(TM) in the development of Plenaxis(TM), its candidate for the treatment of hormonally responsive advanced prostate cancer and endometriosis. PRAECIS also has clinical programs in Alzheimer's disease and non-Hodgkin's lymphoma, and has other programs in the research or preclinical development stage.

This news release contains forward-looking statements, including, but not limited to, statements regarding the re-filing of and continued regulatory review by the United States Food and Drug Administration (FDA) of a New Drug Application for Plenaxis(TM) for the treatment of a defined sub-population of advanced prostate cancer patients. These statements are based on the Company's current beliefs and expectations as to future outcomes. Such statements are subject to numerous factors and uncertainties. These include, but are not limited to, the timing and content of decisions made by the FDA, unexpected results in ongoing and future clinical or preclinical trials and related analyses, and the need for additional research and testing, including as a result of unanticipated determinations by the FDA, as well as the risks set forth from time to time in the Company's filings with the Securities and Exchange Commission, including but not limited to the risks discussed in the Company's Quarterly Report on Form 10-Q for the quarter ended March 31, 2003.

The Abstracts referenced are titled:

(#104072) Abarelix (ABX), a GnRH Antagonist, for the Initial Treatment of Advanced Prostate Cancer Patients (PCPts) - Long Term Follow Up of Anti-Cancer Response Rates (ACR) and Urinary Symptoms in Study 149-98-04. Koch M, Campion M and Garnick MB for the Abarelix Study Group. Indiana University Medical Center, Indianapolis, IN and PRAECIS Pharmaceuticals, Inc. Waltham MA, USA (Abstract sponsored by Dr. Koch)

(#104118) Abarelix (ABX), a GnRH Antagonist, Substantially Reduces Narcotic Analgesic (NA) Requirements and Avoids the Requirement for Bilateral Orchiectomy (BO) in Prostate Cancer Patients (PCPts) with Painful Osseous Metastases (POM). Gaylis F, Campion M and Garnick MB, for the Abarelix Study Group. Center For Urological Research La Mesa, CA, and PRAECIS Pharmaceuticals, Inc. Waltham MA, USA (Abstract sponsored by Dr. Garnick)