Exhibit 99.1

FOR IMMEDIATE RELEASE (Final Draft)

ABGENIX ANNOUNCES 2005 FOURTH QUARTER AND

FULL YEAR FINANCIAL RESULTS

FREMONT, Calif., Feb. 21, 2006 — Abgenix, Inc. (Nasdaq: ABGX) today announced financial results for the fourth quarter and full year ended December 31, 2005. The company reported a net loss of $43.4 million, or $0.48 per share, for the fourth quarter of 2005, compared to a net loss of $42.9 million, or $0.48 per share, for the same period in 2004.

Net cash used in operating activities in the fourth quarter of 2005 was $26.3 million, compared to $18.8 million in the fourth quarter of 2004.  Cash, cash equivalents and marketable securities totaled approximately $332.8 million as of December 31, 2005.

“Positive clinical data for panitumumab and entering into our merger agreement with Amgen were key accomplishments in the fourth quarter of 2005,” said Bill Ringo, president and chief executive officer of Abgenix.  “The pivotal study for panitumumab met its primary endpoint of improving the rate of progression free survival in metastatic colorectal cancer patients who have failed standard chemotherapy.  Based on these study data, we and Amgen initiated our rolling Biologics License Application with the U.S. Food and Drug Administration in December 2005, and expect to complete the filing by the end of first quarter 2006.  With respect to our pending transaction, we believe the proposed acquisition by Amgen delivers substantial value to Abgenix stockholders and will enable panitumumab to achieve its full potential benefit for patients.  We look forward to closing the transaction, subject to stockholder approval, in late March or early April.”

Revenues for the fourth quarter of 2005 were $7.6 million, compared to $5.9 million for the same period in 2004. Revenues for the fourth quarter of 2005 consisted primarily of contract revenues from technology licensing agreements, including a milestone from Pfizer for advancing a XenoMouse®-derived antibody into a pivotal study. For the fourth quarter of 2004, revenues included milestone payments from Human Genome Sciences, Inc., Chiron Corporation and CuraGen Corporation. The company’s revenues typically result from milestone payments and fees associated with various collaborations and technology licensing agreements.

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