Enzon Files sBLA for First-Line Use of ONCASPAR(R); FDA Accepts Application for Review

Enzon Pharmaceuticals, Inc. (Nasdaq: ENZN) announcedtoday that the U.S. Food and Drug Administration (FDA) has acceptedits supplemental biologics license application (sBLA) seeking approvalfor an expanded label for its pediatric oncology product, ONCASPAR, asa first-line therapy for the treatment of patients with acutelymphoblastic leukemia (ALL). Currently, ONCASPAR is indicated forpatients with ALL who require L-asparaginase in their treatmentregimen, but have developed hypersensitivity to the native forms ofL-asparaginase. The Company anticipates that the FDA will take actionon the sBLA during the third quarter of 2006.

"Today's announcement further demonstrates our renewed commitmentto optimizing the potential of our marketed products and to childrenstricken with cancer," said Jeffrey H. Buchalter, Enzon's chairman andchief executive officer. "ONCASPAR is an important drug today in thetreatment of pediatric ALL and we believe this filing supports agreater role for this therapy. We look forward to working closely withthe FDA throughout this review process and making the therapeuticadvantages of ONCASPAR available as a first-line treatment for ALLpatients."

Enzon is supporting its application for this expanded indicationbased on data from two randomized studies conducted by the Children'sCancer Group (CCG), CCG-1962 and CCG-1991, with safety data from morethan 2,000 patients.

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

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

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

About ONCASPAR

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

About Enzon

Enzon Pharmaceuticals, Inc. is a biopharmaceutical companydedicated to the development and commercialization of therapeutics totreat 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 alsoreceives royalties on sales of PEG-INTRON(R), marketed bySchering-Plough Corporation, and MACUGEN(R), marketed by OSIPharmaceuticals and Pfizer Inc. Enzon's product-driven strategyincludes an extensive drug development program that leverages itsproprietary technologies, including a next-generation PEGylationplatform that utilizes linkers designed to release compounds at acontrolled rate. Enzon complements its internal research anddevelopment efforts with strategic initiatives, such as partnershipsdesigned to broaden its revenue base or provide access to promisingnew technologies or product development opportunities. Furtherinformation about Enzon and this press release can be found on theCompany's web site at www.enzon.com.

There are forward-looking statements contained herein that are notbased on historical fact, including without limitation statementscontaining the words "believes," "may," "plans," "will," "estimate,""continue," "anticipates," "intends," "expects," and similarexpressions. Such forward-looking statements involve known and unknownrisks, uncertainties and other factors that may cause actual results,events or developments to be materially different from the futureresults, events or developments discussed above. Among the factorsthat could cause actual result, events or developments to differmaterially are decisions by regulatory authorities regarding whetherand when to approve our drug applications as well as their decisionsregarding labeling and other matters that could affect the commercialpotential of the Company's products. All information in this pressrelease is as of December 1, 2005 and the Company undertakes no dutyto update this information.