Corixa Provides Update On Late Stage Clinical Programs.

Health/Medical Writers

SEATTLE--(BW HealthWire)--June 20, 2001

Results of Year 2000/2001 Data Follow-up For Previously Completed

Pivotal Trial of Melacine Vaccine vs. Observation in

Post-Surgery, Stage II Melanoma Patients

Dialogue With FDA Regarding Possibility of Accelerated Approval of

Melacine in Patients with Specific HLA Gene Expression

Progress of Response to FDA Complete Review Letter for Bexxar BLA 

Corixa Corporation (Nasdaq:CRXA), a developer of immunotherapeutics, today announced the completion of its year 2000 to May 2001 data sweep associated with its completed pivotal trial of Melacine(R) vaccine for Stage II melanoma.

The results of this study -- conducted under a former Ribi ImmunoChem Research, Inc. (now Corixa) investigational new drug application (IND) -- were initially reported by the Southwest Oncology Group (SWOG) in March 2000. The study examined the effects of Melacine vaccination vs. observation in a randomized, controlled trial of 689 Stage II melanoma patients. Patients in the study were randomized to either observation or Melacine therapy following surgical excision of their primary tumor. Surgery results in cure of more than 55 percent of patients with Stage II melanoma, whereas the remainder of the population will relapse. The study closed to accrual in 1996 and initial results were reported when a pre-defined number of events (death or disease recurrence) occurred. Analysis of the data in March 2000 revealed a statistically significant (p=0.04) improvement in disease free survival in favor of Melacine treatment in the intent to treat population (689 patients). A prospectively defined, secondary analysis of the interaction between specific Class I Major Histocompatability Complex (MHC) genes and the product's efficacy also showed a highly statistically significant improvement in disease free survival in patients who expressed either Class I MHC human leukocyte antigen (HLA) A2 or C3 genes (p=0.005). The expression of these immune response genes was previously noted to be associated with beneficial clinical response to Melacine treatment in Phase I and II clinical trials. HLA genes encode proteins that are intimately involved in antigen recognition and immune cell activation and function.

In an effort to provide the U.S. Food and Drug Administration (FDA) and its advisory panel reviewers with as up-to-date a data package as possible, Corixa committed to obtain additional mortality and disease recurrence data on as many patients as possible in the database, prior to proceeding with completion of a Biologics License Application (BLA) filing.

Twenty-seven new events have been noted in the time frame between the trial's final analysis by SWOG and the recent data sweep, of which 18 occurred in the Melacine arm, and nine occurred in the observation arm. Re-analysis of overall disease free survival including these new data, shows that Melacine continues to provide an improvement in overall disease free survival, although the statistical significance of that conclusion has been lost with a convergence of the resultant disease free survival curves (p>0.05).

However, analysis of clinical benefit following completion of the data sweep in patients who were positive for expression of either Class I MHC HLA A2 or C3 genes continues to show a highly statistically significant clinical benefit of Melacine vs. observation in terms of increased disease free survival (p=0.005). Furthermore, Corixa's analyses demonstrated a statistically significant improvement in overall survival in class I MHC HLA A2 or C3 positive patients that received Melacine vs. observation (p=0.003). Expression of either MHC HLA A2 or C3 in the absence of Melacine vaccination was of no clinical benefit to patients, indicating that simple expression of particular MHC haplotypes is not a prognostic factor for positive outcome in this group of patients in the absence of treatment.

"Given the results of the data sweep, we have begun a discussion with FDA regarding the advisability of filing a BLA for accelerated approval of Melacine in patients that express either Class I MHC HLA A2 or C3 genes," stated Steven Gillis, Ph.D., chairman and chief executive officer of Corixa. "Under such a scenario, if approved, Corixa would commit to conducting a confirmatory trial of Melacine vaccine in A2/C3 positive melanoma patients, and perhaps in patients with more advanced disease. We have entered the post-genomic world where one of the outcomes of the genomic revolution is that patient responses to therapies can and should be tailored to the patient's genetic capabilities to respond to such treatments. Patient response to Melacine would appear to be linked to particular MHC genes. MHC genes, often called immune response genes, are highly variable (polymorphic) from individual to individual and are known to be responsible for many of the differences observed in immune responses between individuals."

Gillis added, "The opportunity to provide survival benefit to Stage II melanoma patients as a result of vaccination of individuals that express specific immune response genes makes both scientific and clinical sense. Given that Class I MHC HLA A2 or C3 genes are expressed in between 60 and 70 percent of the U.S. population, this approach could provide clinical benefit to a significant number of cancer patients. We hope that FDA will be supportive of such a regulatory strategy. Once we have had an opportunity to complete our dialogue with the agency, we will determine whether such a filing would be in the best interests of Corixa."

"In addition to Melacine discussions with the FDA, we are making excellent progress on the completion of responses to questions raised by FDA in its complete review letter of March 16, 2001 concerning Bexxar(TM). Answers to many questions are now complete and we are focused on finishing final study reports for two of the three additional studies that we previously announced would be submitted to the agency in response to the complete review letter. The majority of this work is also completed and we are awaiting the results of independent radiology and oncology reviews of response and duration of response data. These reviews have been ongoing and are now nearing completion. We will file our response with the agency when the independent review data is final. We do not expect to provide further updates until we file our response to the complete review letter with FDA."

About Melanoma and Melacine

Malignant melanoma is a highly metastatic and lethal form of skin cancer. It is the most common form of cancer in women between the ages of 25-29 and the second most common form of cancer in women ages 30-34. It is the third most common form of cancer in men ages 35-44. According to the American Cancer Society, cancer of the skin is the most common of all cancers. Melanoma accounts for about 4 percent of skin cancer cases, but causes about 79 percent of skin cancer deaths. The number of new cases of melanoma found in the United States is on the rise. The American Cancer Society predicts that, in the year 2001, there will be close to 50,000 new cases of melanoma in the United States and about 8,000 deaths resulting from melanoma.

Melacine melanoma vaccine consists of lysed (broken) cells from two human melanoma cell lines combined with Corixa's proprietary Detox(R) adjuvant. Detox adjuvant includes MPL(R) adjuvant (monophosphoryl lipid A) and mycobacterial cell wall skeleton, both of which activate the human immune system in the context of vaccination. Melacine, MPL and Detox were acquired by Corixa as part of its purchase of Ribi ImmunoChem Research, Inc., in October 1999. Melacine is approved for sale in Canada for the treatment of Stage IV melanoma.

About Corixa

Corixa is a developer of immunotherapeutics with a commitment to treating and preventing autoimmune diseases, cancer and infectious diseases by understanding and directing the immune system. Corixa is focused on immunotherapeutic products and has a broad technology platform enabling both fully integrated vaccine design and the use of its separate, proprietary product components on a standalone basis. Corixa currently has 16 programs in clinical development and 22 programs in preclinical development, including its most advanced product candidate, Bexxar(TM), a monoclonal antibody conjugated to a radioisotope. The company partners with numerous developers and marketers of pharmaceuticals, targeting products that are Powered by Corixa(TM) technology with the goal of making its potential products available to patients around the world. Corixa was founded in 1994 and is headquartered in Seattle, Wash., with additional operations in Hamilton, Mont. and South San Francisco, Calif. For more information, please visit Corixa's website at www.corixa.com or call the company's investor relations information line at 877/4CORIXA or 877/426-7492.

Forward-Looking Statements

Except for the historical information presented, certain matters discussed in this press release are forward-looking statements. Forward-looking statements are based on the opinions and estimates of management at the time the statements are made. They are subject to certain risks and uncertainties that could cause actual results to differ materially from any future results, performance or achievements expressed or implied by such statements. Factors that could affect Corixa's actual results include, but are not limited to failure of FDA to support the filing of a Melacine BLA for accelerated review in patients with a specific HLA gene expression, failure of FDA to approve Bexxar(TM) for commercial sale and the "Factors Affecting Our Operating Results, Our Business and Our Stock Price," described in our Quarterly Report on Form 10-Q for the quarter ended March 31, 2001, copies of which are available from our investor relations department. Readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date of this release.