Cytogen Announces Initiation of NCI-Sponsored Phase 2 Clinical Trial of QUADRAMET with Targeted Cancer Vaccine for Hormone-Refractory Prostate Cancer.

PRINCETON, N.J. -- Cytogen Corporation (NASDAQ:CYTO) today announced that the National Cancer Institute (NCI), part of the National Institutes of Health (NIH), has initiated a randomized Phase 2 study to evaluate QUADRAMET([R]) (samarium Sm-153 lexidronam injection) in combination with the NIH's targeted therapeutic vaccine, PSA-TRICOM, for patients with progressive hormone-refractory prostate cancer who have failed docetaxel-based regimens.

The primary objective of the study is to determine if there is an improvement in four-month progression-free survival for the combination regimen versus QUADRAMET therapy alone. The study is expected to enroll 68 patients. Currently, there is no standard of care for treating prostate cancer patients who have progressive disease following docetaxel-based therapy.

QUADRAMET is a targeted radiopharmaceutical that is approved for treating pain arising from cancer that has spread to the bone. PSA-TRICOM is a targeted cancer vaccine under development at the NIH and designed to enhance immune system response against tumor cells. PSA-TRICOM targets prostate-specific antigen or PSA, a protein associated with prostate cancer. This novel combination approach is supported by positive preclinical findings that support the combination of QUADRAMET and cancer vaccines for the treatment of prostate, breast, lung, and other cancers.

In April 2006, NCI researchers presented results of a preclinical study at the 97th Annual Meeting of the American Association for Cancer Research. The study, "Use of Samarium-153 (QUADRAMET) to modulate phenotype and enhance killing of tumor cells" demonstrated that exposure to QUADRAMET resulted in up-regulation of surface molecules on cancer cells, including Fas (CD95), carcinoembryonic antigen (CEA), mucin 1 (MUC-1), intercellular adhesion molecule-1 (ICAM-1 or CD54), and major histocompatibility complex class I (MHC-1). Each of the five molecules evaluated in the study has been implicated in enhancing anti-tumor T-cell responses through diverse mechanisms.

Tumor cells can avoid immune system recognition and elimination by down-regulating, or masking or turning off surface molecules involved in immune system attack. The up-regulation, or enhancement, of these surface molecules with QUADRAMET may increase tumor cells' susceptibility to the immune system, and this could be synergistic with various immunotherapy approaches designed to treat cancers. Immunotherapies are designed to stimulate the immune system to recognize and attack cancer cells.

"To date, single-agent immune-based strategies for treating cancer have shown limited promise for treating well-established tumors or advanced disease," said Michael D. Becker, president and chief executive officer of Cytogen. "Published studies indicate that multimodality approaches incorporating immunotherapy, radiotherapy, and other approaches hold the greatest promise for clinical success. Based on existing clinical data demonstrating the safety and preliminary activity of PSA-TRICOM and the preclinical data revealing the synergy between QUADRAMET and immunotherapy, we believe this novel combination is a promising approach to cancer immunotherapy for prostate cancer patients."

The NCI's principal investigator for the study is James L. Gulley, M.D., Ph.D., Director of the Clinical Immunotherapy Group within the Laboratory of Tumor Immunology and Biology. Additional information on the trial, including eligibility requirements, is available by contacting the coordinator at 301-451-1228 or on the internet by following the link below.

http://bethesdatrials.cancer.gov/clinical-research/ search_detail.asp?ProtocolID=NCI-07-C-0106. (Due to its length, this URL may need to be copied/pasted into your Internet browser's address field. Remove the extra space if one exists.)

About PSA-TRICOM

PSA-TRICOM is a targeted cancer therapy designed to stimulate a patient's own immune system to seek out and destroy cancer cells expressing epitopes (antigenic peptide sequences) of prostate-specific antigen (PSA) found in prostate cancer. PSA-TRICOM is designed to introduce the genes for PSA and a TRIad of COstimulatory Molecules (B7-1, ICAM-1 and LFA-3) (TRICOM) - a proprietary triad of costimulatory molecules essential for maximizing the antitumor cellular immune response - into a patient's existing antigen-presenting cells. This stimulates the activation and proliferation of an array of cytotoxic T cells, which seek out and destroy cancer cells bearing any of the targeted epitopes.

About QUADRAMET

QUADRAMET is indicated for the relief of pain in patients with confirmed osteoblastic metastatic bone lesions that enhance on radionuclide bone scan. This press release describes clinical applications that differ from that reported in the QUADRAMET package insert.

QUADRAMET is an oncology product indicated for pain relief that pairs the targeting ability of a small molecule, bone-seeking phosphonate (EDTMP) with the therapeutic potential of radiation (samarium Sm-153). Skeletal invasion by prostate, breast, multiple myeloma, and other cancers often creates an imbalance between the normal process of bone destruction and formation. QUADRAMET selectively targets such sites of imbalance, thereby delivering radioactivity to areas of the skeleton that have been invaded by metastatic tumor.

QUADRAMET has demonstrated a range of characteristics that may be advantageous for the treatment of pain arising from metastatic bone disease, including early onset of pain relief (patients may experience pain relief within the first week with maximal relief generally occurring at three to four weeks after injection), length of pain relief, lasting a median of four months in responding patients, and predictable and reversible bone marrow toxicity or myelosuppression that tends to return to pretreatment levels after eight weeks. QUADRAMET is administered as a single intravenous injection, usually on an outpatient basis, and exhibits selective uptake in areas of bone formation with little or no detectable accumulation in soft tissue.

QUADRAMET Safety Profile

QUADRAMET causes bone marrow suppression. In clinical trials, white blood cell counts and platelet counts decreased to a nadir of approximately 40% to 50% of baseline in 123 (95%) of patients within 3 to 5 weeks after QUADRAMET, and tended to return to pretreatment levels by 8 weeks. Because of the unknown potential for additive effects on bone marrow, QUADRAMET should not be given concurrently with chemotherapy or external beam radiation therapy unless the clinical benefits outweigh the risks. Blood counts should be monitored weekly for at least 8 weeks, or until recovery of adequate bone marrow function. Non-hematologic adverse events that occurred in 5% or more of patients and greater than placebo were pain flare (7%), diarrhea (6%), infection (7%), spinal cord compression (6.5%), arrhythmias (5%), and hematuria (5%). Patients who receive QUADRAMET should be advised that for several hours following administration, radioactivity will be present in excreted urine. To help protect themselves and others in their environment, precautions need to be taken for 12 hours following administration.

A copy of the full prescribing information for QUADRAMET, including warnings, precautions, adverse events and other safety information may be obtained in the U.S. from Cytogen Corporation by calling toll-free 800-833-3533 or by visiting the web site at http://www.cytogen.com, which is not part of this press release.

About Cytogen

Founded in 1980, Cytogen is a biopharmaceutical company dedicated to advancing the treatment and care of cancer patients by building, developing, and commercializing a portfolio of specialty pharmaceutical products. The Company's specialized sales force currently markets QUADRAMET([R]) (samarium Sm-153 lexidronam injection), PROSTASCINT([R])(capromab pendetide), and SOLTAMOX([TM]) (tamoxifen citrate) to the U.S. oncology market. QUADRAMET is approved for the treatment of pain in patients whose cancer has spread to the bone, PROSTASCINTis a PSMA-targeting monoclonal antibody-based agent to image the extent and spread of prostate cancer, and SOLTAMOX is the first liquid hormonal therapy approved in the U.S. for the treatment of breast cancer in adjuvant and metastatic settings. In early 2007, Cytogen plans to introduce its fourth approved oncology product to the U.S. market, CAPHOSOL([R]), an advanced electrolyte solution for the treatment of oral mucositis and dry mouth that is approved in the U.S. as a prescription medical device. The Company is also developing CYT-500, a third-generation radiolabeled antibody to treat prostate cancer. Cytogen's product-focused strategy focuses on attaining sustainable growth through clinical, commercial, and strategic initiatives.

A copy of the full prescribing information for CAPHOSOL, QUADRAMET, PROSTASCINT, and SOLTAMOX, including box warnings, may be obtained in the U.S. from Cytogen Corporation by calling toll free 800-833-3533 or by visiting Cytogen's web site at www.cytogen.com. The Company's website is not part of this press release.

This press release contains certain "forward-looking" statements within the meaning of the Private Securities Litigation Reform Act of 1995 and Section 21E of the Securities Exchange Act of 1934, as amended. All statements, other than statements of historical facts, included in this press release regarding our strategy, future operations, financial position, future revenues, projected costs, prospects, plans and objectives of management are forward-looking statements. Such forward-looking statements involve a number of risks and uncertainties and investors are cautioned not to put any undue reliance on any forward-looking statement. There are a number of important factors that could cause Cytogen's results to differ materially from those indicated by such forward-looking statements. In particular, Cytogen's business is subject to a number of significant risks, which include, but are not limited to: the risk of obtaining the necessary regulatory approvals; the risk of whether products result from development activities; the risk of shifts in the regulatory environment affecting sales of Cytogen's products such as third-party payor reimbursement issues; the risk associated with Cytogen's dependence on its partners for development of certain projects, as well as other factors expressed from time to time in Cytogen's periodic filings with the Securities and Exchange Commission (the "SEC"). As a result, this press release should be read in conjunction with Cytogen's periodic filings with the SEC. The forward-looking statements contained herein are made only as of the date of this press release, and Cytogen undertakes no obligation to publicly update such forward-looking statements to reflect subsequent events or circumstances.