Special Protocol Assessment Supports Initiation of Pivotal Trial Less Than One Year after IND Filed

Cambridge, MA, May 24, 2004 � Therion Biologics Corporation obtained agreement
from the U.S. Food and Drug Administration (FDA) to initiate a Phase III trial of its lead vaccine candidate, PANVAC-VF, for the treatment of metastatic pancreatic cancer in patients who have failed treatment with gemcitabine. The study, the first pivotal trial of a Therion product candidate, is targeted to begin this summer and will be conducted under a Special Protocol Assessment (SPA) by the FDA. The SPA indicates that if the trial successfully meets its primary endpoint, the data will provide the basis for an efficacy claim in a marketing application to the FDA. The study�s primary endpoint will be overall survival compared with best supportive care or palliative chemotherapy.

Therion�s SPA comes less than one year after the company filed the Investigational New Drug Application (IND) for PANVAC-VF. The SPA is based on two recent promising Phase I clinical trials in pancreatic cancer patients, as well as a number of clinical studies with the vaccine�s components. These latter studies, sponsored by the National Cancer Institute (NCI), involved over 200 patients with various tumor types. The results of the two Phase I studies in pancreatic cancer patients will be presented in a poster presentation and reviewed in a panel discussion on June 7 at the Annual Meeting of the American

Society of Clinical Oncology (ASCO) in New Orleans. PANVAC-VF is designed to stimulate the immune system to target and destroy cancer cells expressing two proteins (or antigens), carcinoembryonic antigen (CEA) and mucin-1 (MUC-1), found on over 90 percent of pancreatic tumor cells. The vaccine also incorporates TRICOM�, Therion�s proprietary triad of costimulatory molecules (B7.1, ICAM-1 and LFA-3), to enhance and sustain a targeted immune response against tumor cells.

�This is the first product from Therion�s pipeline to enter pivotal Phase III trials and marks a key milestone on our path towards product commercialization,� said Mark Leuchtenberger, President and Chief Executive Officer of Therion Biologics Corporation.

�Our strategy has been to optimize product candidates through extensive clinical trials of vaccine components and dosing regimens in order to maximize the probability for downstream success. The FDA�s agreement, through the SPA process, with the design of our Phase III trial of PANVAC-VF validates this approach. We are pursuing a similar approach with our second vaccine candidate, PROSTVAC^�-VF, which is currently in Phase II clinical trials for the treatment of prostate cancer.� Pancreatic cancer remains one of the deadliest tumor types, affecting over 30,000 Americans each year. It is the fourth leading cause of cancer death in men and women, with a one-year mortality rate greater than 95 percent. The risk of pancreatic cancer increases with age; most patients are over 50 years old.

�Pancreatic cancer patients face an especially poor prognosis, with few treatment options,� said John Marshall, M.D., Associate Professor of Medicine at Georgetown University Medical Center, who will serve as the lead investigator for the study. �Data from the first trials of PANVAC-VF in advanced pancreatic cancer support moving this vaccine candidate into a large scale randomized trial.�

Study Design
The multicenter, randomized, controlled trial will enroll 250 advanced pancreatic cancer patients who have failed chemotherapy treatment with gemcitabine. Patients will be randomized 1:1 to receive either PANVAC-VF or control treatment. Patients in the treatment arm will receive an initial �priming� dose of PANVAC-VF plus GM-CSF to initiate an anti-cancer immune response, followed by a series of �booster� vaccinations to sustain the response. Control treatment will consist of either best supportive care or palliative chemotherapy (capcitabine, irinotecan or 5-fluorouracil). Secondary study endpoints include safety, quality of life parameters, change in serum tumor antigen levels, response rate and disease stabilization.

Additional Clinical Studies
In addition to pancreatic cancer, Therion vaccines targeting CEA and MUC-1 have been tested in patients with other tumors that are known to over-express the CEA and MUC-1 antigens, including breast, lung and colorectal cancers. Therion and the NCI are currently planning up to 18 additional trials with PANVAC-VF in these indications.

About Therion Biologics Corporation
Therion Biologics Corporation develops therapeutic vaccines that aim to extend and improve the lives of cancer patients. The company has two lead product candidates: PANVAC-VF, entering Phase III clinical trials for pancreatic cancer; and PROSTVAC^�-VF in Phase II clinical trials for prostate cancer. The company is applying its technology to develop its vaccine pipeline, including treatments for breast cancer, lung cancer and AIDS. Therion is also developing a vaccine for colon cancer with its strategic partner, Aventis Pasteur, Ltd. Through Therion�s longstanding partnerships with the National Cancer Institute (NCI) and a network of renowned clinical institutions, over 700 patients in more than 30 clinical trials have been treated with Therion�s vaccine candidates.