Coulter Pharmaceutical Announces Positive Phase III Investigational Trial Results For Bexxar in Non-Hodgkin's Lymphoma.

PALO ALTO, Calif.--(BW HealthWire)--Oct. 20, 1998--

Unique Monoclonal Antibody/Radiation Therapy Provides Longer

Duration of Cancer Remission

Coulter Pharmaceutical, Inc. (Nasdaq:CLTR) today announced positive results from a Phase III investigational trial of Bexxar(tm) (iodine I 131 tositumomab) in non-Hodgkin's lymphoma (NHL) patients who were refractory to chemotherapy.

The results indicate that statistical significance was reached for the primary and secondary clinical endpoints. Bexxar is a unique therapy which combines the specificity of monoclonal antibody technology with the power of radiation to treat cancer. The company intends to present the Phase III results in detail at the American Society of Hematology meeting in December.

"The results demonstrate Bexxar's ability to provide patients with longer durations of remission compared to their most recent chemotherapy," said Michael F. Bigham, president and chief executive officer of Coulter. "These longer durations of remission with Bexxar suggest a reversal of the natural history of the disease wherein patients typically experience a shorter duration of remission with each subsequent therapy. The data are all the more compelling given that the patients in this trial had received on average over four previous regimens of chemotherapy, including salvage treatments. We are preparing the data as quickly as possible for review by the Food and Drug Administration."

The Phase III investigational trial included 60 NHL patients who were refractory to chemotherapy, having either no response to prior chemotherapy, or disease progression within six months of their last chemotherapy regimen. The primary clinical endpoint was the comparison between the patient's duration of response on Bexxar(tm) and duration of response on the patient's prior chemotherapy, as assessed by a masked, randomized review of efficacy data by an independent panel of physicians. Of the 41 cases where response durations to chemotherapy and Bexxar were not equivalent, 32 patients (78 percent) experienced a longer duration of response to Bexxar compared to only nine patients (22 percent) who experienced a longer duration of response to prior chemotherapy (p less than 0.001). The remaining 19 patients in the trial had equivalent duration of response to Bexxar and prior chemotherapy.

The overall response rate, a secondary clinical endpoint, also was significantly greater on Bexxar with 67 percent of patients responding to Bexxar compared to only 28 percent of patients responding to prior chemotherapy (p less than 0.001).

Side effects related to Bexxar included a decrease in blood counts which were reversible and generally self-limiting. A minority of these heavily pre-treated patients required support by blood cell transfusion or growth factor. A mild flu-like syndrome also was observed in some patients.

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. It is believed that through this targeted approach, the tumor cells receive a greater concentration of the therapeutic radiation from Bexxar relative to normal tissues. The antibody treatment is administered in a regimen which consists of two intravenous doses given about one week apart -- first a dosimetric dose followed by a therapeutic dose. This is in contrast to conventional chemotherapy where treatment is given repeatedly over several months.

In September, the company announced the initiation of an Expanded Access Program which allows patients and physicians access to Bexxar during the period prior to potential FDA marketing approval. The program is expected to eventually include over 100 community and academic oncology centers across the United States and will provide access to Bexxar for relapsed and refractory patients with low-grade and transformed low-grade NHL who are seeking alternative therapies.

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 from the National Cancer Institute, approximately 270,000 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. There are approximately 54,000 new cases of NHL diagnosed each year.

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 product candidate is Bexxar(tm) (iodine I 131 tositumomab), a monoclonal antibody conjugated to a radioisotope. Initial efforts in the targeted oncologies 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 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.