Cell Genesys, Inc. To Present Data From Two GVAX(R) Cancer Immunotherapy Clinical Trials At 2006 American Society of Clinical Oncology Annual Meeting

SOUTH SAN FRANCISCO, Calif., March 13 /PRNewswire-FirstCall/ -- Cell Genesys, Inc. today announced that its two abstracts have been accepted as oral presentations at the 2006 American Society of Clinical Oncology (ASCO) Annual Meeting which will take place in Atlanta, GA on June 2 -6, 2006. The abstracts to be presented are as follows:

-- A dose-escalation trial of GM-CSF-gene transduced allogeneic prostate cancer cellular immunotherapy in combination with a fully human anti-CTLA-4 antibody (MDX-010, ipilimumab) in patients with metastatic hormone-refractory prostate cancer (HRPC) (Clinical Science Symposium oral session on June 3, 2006) -- K562/GM-CSF vaccination reduces tumor burden, including achieving molecular remissions in chronic myelogenous leukemia (CML) patients with residual disease on imatinib (Oral presentation on June 3, 2006)

“We are pleased that we will have the opportunity to present interim data from the first combination trial of our GVAX immunotherapy for prostate cancer and MDX-010, a fully human antibody that stimulates the immune system, which is being developed by our collaborators at Medarex and Bristol Myers Squibb, and we are also glad to have the opportunity to provide an update on our GVAX immunotherapy for leukemia program in CML,” stated Joseph J. Vallner, Ph.D., president and chief operating officer of Cell Genesys. “We continue to be fortunate to have the resources we need to pursue multiple clinical stage product opportunities in parallel, including the ongoing Phase 3 trials for our lead program in prostate cancer.”

Cell Genesys is currently enrolling two Phase 3 clinical trials of GVAX immunotherapy for prostate cancer in approximately 1200 patients with metastatic HRPC, comprising one of the largest Phase 3 clinical programs ever conducted in men with advanced prostate cancer. This program is supported by the median survival results from two, independent, multi-center Phase 2 clinical trials in approximately 115 patients that are not only consistent with each other, but also compare favorably to the previously published median survival of 18.9 months for metastatic hormone-refractory prostate cancer patients treated with Taxotere(R) (docetaxel) chemotherapy plus prednisone, the current standard of care. Additionally, the company recently presented an analysis of these survival data based on a published, validated nomogram that demonstrates that the survival results exceeded the predicted median survival by approximately 7 months in both trials. The company’s ongoing Phase 3 program is designed to confirm a potential survival benefit for GVAX immunotherapy for prostate cancer.

Cell Genesys is currently evaluating GVAX cancer immunotherapy for leukemia in a Phase 2 clinical trial in patients with chronic myelogenous leukemia (CML) who have been treated with Gleevec(R) (imatinib mesylate) for at least one year. The goal of GVAX immunotherapy in this program is to reduce or eliminate residual disease after Gleevec therapy. Preliminary findings from this trial indicated that the addition of the immunotherapy to Gleevec therapy reduced persistent leukemic disease in 9 of 19 patients to date as demonstrated by a complete disappearance (five patients) or a greater than one log (90%) reduction (four patients) in bcr-abl -- a validated genetic marker found on the leukemic cells. Reductions of bcr-abl have been previously shown to be strongly associated with improved progression-free survival in CML patients treated with Gleevec.

Clinical trials of GVAX(R) cancer immunotherapies are under way for multiple types of cancer including prostate cancer, pancreatic cancer, and leukemia. These products are whole-cell immunotherapies which are designed to stimulate an immune response against the patient’s tumor. The products are comprised of tumor cells that have been irradiated and genetically modified to secrete GM-CSF (granulocyte-macrophage colony stimulating factor), an immune stimulatory hormone which plays a key role in stimulating the body’s response to such immunotherapies. GVAX cancer immunotherapies are being developed as non patient-specific, “off-the-shelf” pharmaceutical products.

Cell Genesys is focused on the development and commercialization of novel biological therapies for patients with cancer. The company is currently pursuing two clinical stage product platforms -- GVAX(R) cancer immunotherapies and oncolytic virus therapies. Ongoing clinical trials include Phase 3 trials of GVAX immunotherapy for prostate cancer, Phase 2 trials of GVAX immunotherapy for pancreatic cancer and leukemia, and a Phase 1 trial of CG0070 oncolytic virus therapy for bladder cancer. Cell Genesys continues to hold an equity interest in its former subsidiary, Ceregene, Inc., which is developing gene therapies for neurodegenerative disorders. Cell Genesys is headquartered in South San Francisco, CA and has its principal manufacturing operation in Hayward, CA. For additional information, please visit the company’s website at www.cellgenesys.com.

Statements made herein about the company, other than statements of historical fact, including statements about the company’s progress, results and timing of clinical trials and preclinical programs and the nature of product pipelines are forward-looking statements and are subject to a number of uncertainties that could cause actual results to differ materially from the statements made, including risks associated with the success of clinical trials and research and development programs, the regulatory approval process for clinical trials, competitive technologies and products, patents, continuation of corporate partnerships and the need for additional financings. For information about these and other risks which may affect Cell Genesys, please see the company’s Annual Report on Form 10-K for the year ended December 31, 2004 filed on March 14, 2005 as well as Cell Genesys’ reports on Form 10-Q and 8-K and other reports filed from time to time with the Securities and Exchange Commission. The company assumes no obligation to update the forward-looking information in this press release.

Contact: Ina Cu, Investor Relations of Cell Genesys, +1-650-266-3200.

Cell Genesys, Inc.

CONTACT: Ina Cu, Investor Relations of Cell Genesys, +1-650-266-3200

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