Elspar

BRIDGEWATER, N.J. -- Enzon Pharmaceuticals, Inc. (Nasdaq: ENZN) announced today that the U.S. Food and Drug Administration (FDA) has accepted its supplemental biologics license application (sBLA) seeking approval for an expanded label for its pediatric oncology product, ONCASPAR, as a first-line therapy for the treatment of patients with acute lymphoblastic leukemia (ALL). Currently, ONCASPAR is indicated for patients with ALL who require L-asparaginase in their treatment regimen, but have developed hypersensitivity to the native forms of L-asparaginase. The Company anticipates that the FDA will take action on the sBLA during the third quarter of 2006.

"Today's announcement further demonstrates our renewed commitment to optimizing the potential of our marketed products and to children stricken with cancer," said Jeffrey H. Buchalter, Enzon's chairman and chief executive officer. "ONCASPAR is an important drug today in the treatment of pediatric ALL and we believe this filing supports a greater role for this therapy. We look forward to working closely with the FDA throughout this review process and making the therapeutic advantages of ONCASPAR available as a first-line treatment for ALL patients."

Enzon is supporting its application for this expanded indication based on data from two randomized studies conducted by the Children's Cancer Group (CCG), CCG-1962 and CCG-1991, with safety data from more than 2,000 patients.

CCG-1962 is a randomized controlled study comparing ONCASPAR versus native L-asparaginase (Elspar(R)) for the first-line treatment of pediatric ALL patients. The observed advantages of ONCASPAR versus native L-asparaginase in CCG-1962 included a lower incidence of neutralizing antibodies, more rapid clearance of lymphoblasts from the bone marrow, and a more convenient dosing schedule. Enzon is using the data from CCG-1962 to support its sBLA for ONCASPAR with efficacy data from 118 patients. The CCG-1962 study was published in the March 2002 issue of Blood, a publication of the American Society of Hematology.

The observed advantages of ONCASPAR in the CCG-1962 study led to the use of ONCASPAR in a subsequent study, CCG-1991. CCG-1991 is a multi-arm study using ONCASPAR in the first-line setting. Enzon is using the interim results from CCG-1991 to support its sBLA for ONCASPAR with safety data from over 2,000 patients. A detailed analysis of the CCG-1991 study is being reviewed for publication in a major medical journal.

An estimated 35,000 new cases of leukemia will have been diagnosed in the United States during 2005. Of these about 4,000 will have been acute lymphoblastic leukemia (also called acute lymphocytic leukemia or ALL). Although ALL is mainly a childhood leukemia, about one-third of new cases will occur in adults.

About ONCASPAR

ONCASPAR is a PEG-enhanced version of the naturally occurring enzyme L-asparaginase. L-asparaginase is an enzyme that depletes the amino acid asparagine, which certain leukemic cells are dependent upon for survival. ONCASPAR was granted a marketing license by the U.S. Food and Drug Administration in February 1994 to treat patients with acute lymphoblastic leukemia who require L-asparaginase in their treatment regimen, but have developed hypersensitivity to native forms of L-asparaginase. Through its proprietary PEGylation technology, Enzon designed ONCASPAR to offer therapeutic advantages over unmodified L-asparaginase. In addition to reduced immunogenicity, ONCASPAR provides a more convenient, patient-friendly dosing regimen that allows for administration every 14 days, versus twice weekly for unmodified L-asparaginase. Enzon's specialized oncology sales force markets ONCASPAR in North America.

About Enzon

Enzon Pharmaceuticals, Inc. is a biopharmaceutical company dedicated to the development and commercialization of therapeutics to treat patients with cancer and other life-threatening diseases. Enzon's specialized sales force markets ABELCET(R), ONCASPAR(R), ADAGEN(R), and DEPOCYT(R) in North America. In addition, Enzon also receives royalties on sales of PEG-INTRON(R), marketed by Schering-Plough Corporation, and MACUGEN(R), marketed by OSI Pharmaceuticals and Pfizer Inc. Enzon's product-driven strategy includes an extensive drug development program that leverages its proprietary technologies, including a next-generation PEGylation platform that utilizes linkers designed to release compounds at a controlled rate. Enzon complements its internal research and development efforts with strategic initiatives, such as partnerships designed to broaden its revenue base or provide access to promising new technologies or product development opportunities. Further information about Enzon and this press release can be found on the Company's web site at www.enzon.com.

There are forward-looking statements contained herein that are not based on historical fact, including without limitation statements containing the words "believes," "may," "plans," "will," "estimate," "continue," "anticipates," "intends," "expects," and similar expressions. Such forward-looking statements involve known and unknown risks, uncertainties and other factors that may cause actual results, events or developments to be materially different from the future results, events or developments discussed above. Among the factors that could cause actual result, events or developments to differ materially are decisions by regulatory authorities regarding whether and when to approve our drug applications as well as their decisions regarding labeling and other matters that could affect the commercial potential of the Company's products. All information in this press release is as of December 1, 2005 and the Company undertakes no duty to update this information.

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