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Interim Phase 2 Data Show Panitumumab Has Single-Agent Antitumor Activity in Metastatic Colorectal Cancer; Response Appears Independent of Prior Chemotherapy Regimen

Additional Interim Phase 2 Data in Advanced
Non-Small Cell Lung Cancer Presented
NEW ORLEANS--June 6, 2004-- Amgen Inc. (Nasdaq:AMGN), the world's largest biotechnology company, and Abgenix (Nasdaq:ABGX), a leading antibody development company, today announced interim data from an ongoing Phase 2 study demonstrating that panitumumab (formerly ABX-EGF), a fully human monoclonal antibody, has antitumor activity when administered as a single-agent treatment to patients with metastatic colorectal cancer who have failed chemotherapy.

The updated analysis showed that patients with measurable metastatic colorectal cancer which expressed the epidermal growth factor receptor (EGFr) experienced partial responses. Response rates were similar for patients treated with either two or three prior chemotherapy agents. The results confirm earlier interim findings from this study and were presented by the study's lead investigator, J. Randolph Hecht, M.D., Director of the Gastrointestinal (GI) Oncology Program at UCLA's Jonsson Comprehensive Cancer Center, in a poster presentation at the 40th American Society of Clinical Oncology (ASCO) Annual Meeting. (ASCO Abstract #3511)

"This is an exciting time in colorectal cancer research as we continue to see the development of new promising targeted therapies," said Hecht. "In this study, panitumumab showed durable responses and was well-tolerated in colorectal cancer patients. We are encouraged because we have not seen anaphylaxis in patients receiving panitumumab, and infusion reactions have been uncommon thus far."

Patients in the study (n=148) were previously treated with 5FU (with or without leucovorin) and either irinotecan or oxaliplatin, or both. Patients received 2.5 mg/kg of panitumumab by weekly intravenous infusion. Tumor responses were confirmed approximately four weeks after the initial response was observed.

"Response to panitumumab appears to be independent of prior treatment with oxaliplatin, indicating potential utility in refractory colorectal cancer patients," added Hecht.

Treatment with panitumumab resulted in a 10 percent overall response rate (15 partial, 0 complete) with a median duration of response of 5.2 months. Stabilization of disease was observed in 38 percent of patients (n=56). Median overall time to progression was two months and median overall survival was 7.9 months. Exploratory subgroup analyses comparing responses in patients who had received two prior chemotherapy agents (9/80) versus those who had received three prior agents (6/68), demonstrated similar efficacy (overall partial response rate of 11 percent versus 9 percent, respectively).

In this study, panitumumab was well-tolerated, with reversible skin rash as the most common side effect (95 percent, 3.4 percent grade 3). Other side effects experienced by some patients were fatigue, nausea and mild diarrhea. One patient had a grade 3 infusion-related reaction related to panitumumab. There were no instances of anaphylaxis. In those patients tested to date (n=110), no human antihuman antibodies (HAHAs) have been observed.

Further Analysis Suggests Panitumumab is Well-Tolerated in Advanced Non-Small Cell Lung Cancer

Data from Part 1 of a second Phase 2 study demonstrated that frontline therapy with panitumumab was generally well-tolerated in combination with paclitaxel and carboplatin in patients with advanced non-small cell lung cancer (NSCLC). The results were presented by Jeffrey Crawford, M.D., Professor of Medicine and Interim Chief of Medical Oncology at the Duke University Medical Center, in a poster at the 40th ASCO Annual Meeting. (ASCO Abstract #7083)

"We are encouraged by the safety profile of this antibody in lung cancer patients when given in combination with chemotherapy, which we believe reflects its fully human nature. We look forward to the results of the second part of this ongoing and now accrued study, which will evaluate the efficacy of panitumumab in combination with chemotherapy," said Crawford.

Nineteen patients were enrolled into three groups: those administered 1.0 mg/kg (n=6), 2.0 mg/kg (n=7), and 2.5 mg/kg (n=6) panitumumab weekly for three weeks, for up to six cycles. Five of 19 patients had objective responses (one complete, four partial). In this small study of 19 patients, the observed median time to progression was six months and the observed median overall survival was 17 months. The most common adverse event seen in this study was skin rash, but the incidence of grade 3 skin rash did not appear to increase with dose. Part 2 of this study (n=175) is designed to confirm these findings and compares time to progression for patients receiving panitumumab plus chemotherapy to that for patients receiving chemotherapy alone as frontline therapy for advanced NSCLC.

About Panitumumab

Co-developed by Amgen and Abgenix, panitumumab is an investigational product in a new class of targeted cancer treatments called epidermal growth factor receptor (EGFr) inhibitors. Panitumumab (formerly ABX-EGF), which was generated with XenoMouse(R)(1) technology, is the first fully human monoclonal antibody directed against EGFr and is being evaluated as both a monotherapy and in combination with other agents for the treatment of various types of cancer, including colorectal, lung and kidney. Amgen initiated pivotal trials in the United States and Europe evaluating panitumumab as third-line monotherapy in colorectal cancer patients in January 2004.

About Amgen

Amgen is a global biotechnology company that discovers, develops, manufactures and markets important human therapeutics based on advances in cellular and molecular biology.

About Abgenix

Abgenix is a biopharmaceutical company focused on the discovery, development and manufacturing of human therapeutic antibodies. The company's antibody development platform includes a leading technology and state-of-the-art manufacturing capabilities that enable the rapid generation, selection and production of high affinity, fully human antibody product candidates to a variety of disease targets. Abgenix leverages its leadership position in human antibody technology to build a diversified product portfolio through the establishment of collaborations with multiple pharmaceutical and biotechnology companies. For more information on Abgenix, visit the company's Web site at www.abgenix.com.

Amgen Forward Looking Statement

This news release contains forward-looking statements that involve significant risks and uncertainties, including those discussed below and others that can be found in Amgen's Form 10-K for the year ended December 31, 2003, and in Amgen's periodic reports on Form 10-Q and Form 8-K. Amgen is providing this information as of the date of this news release and does not undertake any obligation to update any forward-looking statements contained in this document as a result of new information, future events or otherwise.

No forward-looking statement can be guaranteed and actual results may differ materially from those we project. Discovery or identification of new product candidates or development of new indications for existing products cannot be guaranteed and movement from concept to product is uncertain; consequently, there can be no guarantee that any particular product candidate or development of a new indication for an existing product will be successful and become a commercial product. Further, preclinical results do not guarantee safe and effective performance of product candidates in humans. The complexity of the human body cannot be perfectly, or sometimes, even adequately modeled by computer or cell culture systems or animal models. The length of time that it takes for us to complete clinical trials and obtain regulatory approval for product marketing has in the past varied and we expect similar variability in the future. We develop product candidates internally and through licensing collaborations, partnerships and joint ventures. Product candidates that are derived from relationships may be subject to disputes between the parties or may prove to be not as effective or as safe as we may have believed at the time of entering into such relationship. Also, we or others could identify side effects or manufacturing problems with our products after they are on the market. In addition, sales of our products are affected by the availability of reimbursement and the reimbursement policies imposed by third party payors, including governments, private insurance plans and managed care providers, and may be affected by domestic and international trends toward managed care and healthcare cost containment as well as possible US legislation affecting pharmaceutical pricing and reimbursement. Government regulations and reimbursement policies may affect the development, usage and pricing of our products. In addition, we compete with other companies with respect to some of our marketed products as well as for the discovery and development of new products. We believe that some of our newer products, product candidates or new indications for existing products, may face competition when and as they are approved and marketed. Our products may compete against products that have lower prices, established reimbursement, superior performance, are easier to administer, or that are otherwise competitive with our products. In addition, while we routinely obtain patents for our products and technology, the protection offered by our patents and patent applications may be challenged, invalidated or circumvented by our competitors and there can be no guarantee of our ability to obtain or maintain patent protection for our products or product candidates. We cannot guarantee that it will be able to produce commercially successful products or maintain the commercial success of our existing products. Our stock price may be affected by actual or perceived market opportunity, competitive position, and success or failure of our products or product candidates. Further, the discovery of significant problems with a product similar to one of our products that implicate an entire class of products could have a material adverse effect on sales of the affected products and on our business and results of operations.

The scientific information discussed in this news release related to our product candidates is preliminary and investigative. Such product candidates are not approved by the U.S. Food and Drug Administration (FDA), and no conclusions can or should be drawn regarding the safety or effectiveness of the product candidates. Only the FDA can determine whether the product candidates are safe and effective for the use(s) being investigated. Further, the scientific information discussed in this news release relating to new indications for our products is preliminary and investigative and is not part of the labeling approved by the U.S. Food and Drug Administration (FDA) for the products. The products are not approved for the investigational use(s) discussed in this news release, and no conclusions can or should be drawn regarding the safety or effectiveness of the products for these uses. Only the FDA can determine whether the products are safe and effective for these uses. Healthcare professionals should refer to and rely upon the FDA-approved labeling for the products, and not the information discussed in this news release.

Abgenix Forward Looking Statement

Statements made in this press release about Abgenix's technologies, product development activities and collaborative arrangements, other than statements of historical fact, are forward-looking statements and are subject to a number of uncertainties that could cause actual results to differ materially from the statements made, including risks associated with the success of clinical trials, the progress of research and product development programs, product manufacturing, regulatory approval processes, competitive products and services and the extent and breadth of Abgenix's patent portfolio. Please see Abgenix's public filings with the Securities and Exchange Commission for information about risks that may affect Abgenix.

EDITOR'S NOTE: An electronic version of this news release may be accessed via our Web site at www.amgen.com. Journalists and media representatives may sign up to receive all news releases electronically at time of announcement by filling out a short form in the Media section of the Web site.

(1) XenoMouse(R) is a registered trademark of Xenotech, a wholly

owned subsidiary of Abgenix, Inc.

Trish Hawkins, 805-447-4587 (media)
Investor Relations, 805-447-1060 (investors)
Ami Knoefler, 510-284-6350 or 510-284-6605
(media & investors)

SOURCE: Amgen Inc. and Abgenix