Coulter Pharmaceutical Initiates Phase II Re-Treatment Trial With Bexxar.

PALO ALTO, Calif.--(BW HealthWire)--June 23, 1998--Coulter Pharmaceutical (NASDAQ:CLTR) today announced that it has begun a Phase II multicenter investigational trial in non-Hodgkin's lymphoma patients previously treated with Bexxar(TM) (iodine I 131 tositumomab).

In this new trial, these patients will be re-treated with the therapy.

"While many patients are experiencing ongoing long-term, durable complete remissions from a single therapeutic dose of Bexxar, this trial allows those patients who have relapsed from the therapy another chance for a Bexxar-induced remission," said Michael F. Bigham, president and chief executive officer of Coulter Pharmaceutical.

"We were encouraged by earlier data generated in a smaller study which demonstrated that complete remissions can be achieved again with Bexxar and that a second Bexxar treatment was well-tolerated, with patients

experiencing bone marrow recovery approximately eight weeks following both their first and second Bexxar treatments. We look forward to gathering additional data on the potential of repeatedly using Bexxar to gain the efficacy benefits of the therapy while preserving the quality of life of patients."

The open-label trial will include all histologies: low-, intermediate- and high-grade non-Hodgkin's lymphoma patients who relapsed from their initial Bexxar treatment and who wish to have access to the therapy again. Patients entering the trial must be negative for seroconversion to the antibody to be eligible for the re-treatment study.

In a published abstract for the American Society of Clinical Oncology in May 1998, the company reported on successful re-treatment with Bexxar in patients who have relapsed from their initial Bexxar treatment. These patients had on average failed five prior chemotherapies before being treated with Bexxar.

Data from 13 re-treated patients revealed that eight of 13 (62 percent) patients responded to re-treatment with four of 13 (31 percent) patients experiencing a complete remission with the second Bexxar treatment. In patients who had achieved a complete remission after their initial Bexxar treatment, five of six (83 percent) experienced an overall response with three of six (50 percent) achieving a second complete remission.

Bexxar was well-tolerated, with side effects consisting of mild-to-moderate, transient flu-like syndrome and reversible low blood cell counts. One patient tested positive for a seroconversion to antibody following re-treatment.

Coulter Pharmaceutical Inc. is engaged in the development of novel drugs and therapies for the treatment of people with cancer. The company currently is developing a family of cancer therapeutics based upon two drug development programs: therapeutic antibodies and targeted oncologics.

The company's most advanced investigational biologic product candidate is Bexxar(TM) (iodine I 131 tositumomab), a monoclonal antibody conjugated to a radioisotope. The company intends to file a BLA for Bexxar by the end of 1998. Initial efforts in the targeted oncologics program are focused on the development of a tumor-activated peptide pro-drug version of doxorubicin to potentially treat certain solid tumor cancers.

Except for the historical information contained herein, the matters discussed in this news release are forward-looking statements that involve risks and uncertainties, including uncertainties related to product development, uncertainties related to the need for regulatory and other government approvals, dependence on proprietary technology, uncertainty of market acceptance of Bexxar(TM) or the company's other product candidates and other risks detailed from time to time in the company's filings with the Securities and Exchange Commission (SEC). In particular, see "Risk Factors" in the company's Annual Report on Form 10-K for the year ended December 31, 1997.

    CONTACT: Coulter Pharmaceutical Inc.
              Sylvia Wheeler, 650/842-7306