Coulter Pharmaceutical Reports Follow-Up Data On 432 Patients Treated With Bexxar.

SOUTH SAN FRANCISCO, Calif.--(BW HealthWire)--June 7, 1999--

Coulter Pharmaceutical, Inc. (Nasdaq:CLTR) today announced follow-up data on non-Hodgkin's lymphoma (NHL) patients treated with the company's lead cancer therapy in development, Bexxar(TM) (tositumomab and iodine I 131 tositumomab). The long-term follow-up data from patients treated in all of the company's clinical trials were presented on Saturday by Nancy Valente, M.D., associate director of clinical research at Coulter Pharmaceutical, at the International Conference on Malignant Lymphoma held in Lugano, Switzerland.

Dr. Valente reported that Bexxar has been administered to 432 NHL patients at approximately 40 centers throughout the United States and United Kingdom. Most of these patients were heavily pre-treated with a median of three prior chemotherapy regimens. At the time of the analysis, 249 of the 432 patients (58 percent) were free of disease progression.

Dr. Valente also reported that subsequent therapies have been administered following Bexxar treatment and that generally neither the low blood counts nor HAMA positive readings associated with Bexxar precluded patients from receiving other therapies. Of the 432 patients, 183 had progressed following Bexxar treatment at the time of this analysis. One-hundred-fifty-six (156) of the 183 patients who progressed received greater than 300 subsequent therapies, including re-treatment with Bexxar, single agent or combination chemotherapy, radiation therapy, Rituximab, bone marrow or stem cell transplant, biological therapy, and/or steroid therapy. The majority of patients (101 patients or 65 percent) went on to receive chemotherapy following Bexxar. The chemotherapy regimens included combination and salvage therapies such as ESHAP, DHAP, and FND. Twenty patients (13 percent) were re-treated with Bexxar. Fifteen patients (10 percent) underwent stem cell or bone marrow transplants. Forty-one patients (25 percent), six of whom were known to be HAMA positive, received Rituximab as a subsequent therapy. There was no correlation between HAMA positivity and either infusion reaction or response to Rituximab. Twenty-five of the 183 patients were not treated with subsequent therapy primarily due to slowly progressive disease not requiring therapy. Only one patient did not receive subsequent therapy due to low blood counts.

Short-term side effects associated with Bexxar(TM) included a decrease in blood counts which were generally reversible and self-limiting. Only five percent of patients experienced platelet counts less than 10,000 cells/mm(3), with a minority of patients requiring support by blood cell transfusion of growth factor. Additional short term side effects included a mild to moderate flu-like syndrome which was observed in approximately one-third of patients. Longer-term side effects were infrequent and included increases in thyroid stimulating hormone (TSH) in a small percentage of patients. Myelodysplastic syndrome also was noted in a small percentage of patients for which the cytogenetics of analyzed cases were generally consistent with previous exposure to chemotherapeutic agents, i.e. alkylating agents or etoposide. Human anti-mouse antibodies (HAMA) were detected in nine previously treated patients (six percent). As expected, a higher HAMA rate was observed in previously untreated patients with 35 patients (54 percent) of this patient population testing positive for this laboratory test.

"These data continue to support Bexxar's potential as a new treatment option for low-grade and transformed low-grade non-Hodgkin's lymphoma," said Michael F. Bigham, president and chief executive officer at Coulter.

Bexxar is currently under investigation for the treatment of low-grade and transformed low-grade NHL. Coulter Pharmaceutical completed a Phase III clinical trial of Bexxar(TM) and is preparing a Biologics License Application to seek marketing licensure for the treatment of relapsed and refractory, low-grade or transformed low-grade non-Hodgkin's lymphoma from the U.S. Food and Drug Administration. In December 1998, Coulter and SmithKline Beecham (SB) established a partnership to jointly market Bexxar in the United States following regulatory approval with the two companies sharing equally in profits. Outside the United States, excluding Japan, Coulter has granted SB exclusive marketing and distribution rights in return for product royalties.

Bexxar, which is an antibody conjugated to iodine 131, attaches to a protein found only on the surface of B-cells, including both non-Hodgkin's lymphoma B-cells and some normal B-cells. Bexxar is believed to work through a dual mechanism of action resulting from the immune system activity of the monoclonal antibody and the therapeutic effects of the iodine (I-131) radioisotope. Through Bexxar's targeted approach, the tumor cells receive a greater concentration of the therapeutic radiation from the therapy relative to normal tissues.

Non-Hodgkin's lymphoma is a form of cancer that affects the blood and lymph tissues. NHL currently is the sixth leading cause of death among cancers in the United States and has the second fastest growing mortality rate. According to statistics form the National Cancer Institute, approximately 300,000 people are afflicted with NHL in the United States alone. Of the total, the company estimates that approximately 140,000 people have low-grade or transformed low-grade disease.

Coulter Pharmaceutical, Inc. is engaged in the development of novel drugs and therapies for the treatment of cancer and autoimmune diseases. The company currently is developing a family of therapeutics based upon two drug development programs: therapeutic antibodies and targeted oncologics. The company's most advanced product candidate is Bexxar(TM), a monoclonal antibody conjugated to a radioisotope for the treatment of non-Hodgkin's lymphoma. 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. The company's therapeutic antibody program includes an antibody-based approach to block the Type I interferon receptor for the treatment of autoimmune diseases and transplant rejection.

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 most recently filed Form 10K.