Pivotal Trial in Medullary Thyroid Cancer Planned to Initiate This Summer

SOUTH SAN FRANCISCO, Calif., June 16 /PRNewswire-FirstCall/ -- Exelixis, Inc. (Nasdaq: EXEL) announced today that the company and the U.S. Food and Drug Administration (FDA) have reached agreement on the phase 3 registration trial of XL184, a small molecule anticancer compound targeting MET, RET, and VEGFR2, via the Special Protocol Assessment process. Exelixis has also discussed the trial design with European regulatory agencies. Exelixis is planning to initiate the phase 3 trial of XL184 as a potential treatment for medullary thyroid cancer (MTC) this summer.

The phase 3 trial has been designed in collaboration with internationally renowned experts in the field of thyroid malignancies, including Dr. Steven Sherman from the MD Anderson Cancer Center in Houston, Texas, Drs. Douglas Ball and Barry Nelkin from Johns Hopkins University in Baltimore, Maryland, and Dr. Martin Schlumberger from the Institut Gustave Roussy in Paris, France. This will be a randomized, placebo-controlled, double-blinded study of XL184 as single-agent therapy in 315 patients with unresectable, locally advanced, or metastatic MTC. Patients will be randomized in a 2:1 ratio to receive XL184 or placebo administered as a daily oral dose. The primary endpoint will be duration of progression-free survival. In a planned event-driven analysis, the study size provides 90% power to detect a 75% increase in progression-free survival in patients with documented progressive disease prior to study entry. Secondary endpoints will include overall survival, objective tumor response rate, and changes in serum biomarkers (carcinoembryonic antigen and calcitonin). Additional secondary endpoints will be assessment of the potential relationship between germline and/or tumor DNA sequence alterations and the efficacy of XL184, as well as assessment of pharmacodynamics and pharmacokinetics of XL184. It is expected that approximately 100 sites in 20 countries will participate in this study.

"We are very encouraged by the level of clinical activity in the ongoing XL184 phase 1 study showing a high response rate and durable disease control in medullary thyroid cancer patients, and believe that the FDA-approved phase 3 study design will allow us to rigorously evaluate the clinical benefit of XL184 in this population for which no standard of care is available," said Gisela Schwab, MD, executive vice president and chief medical officer at Exelixis.

The planned initiation of this phase 3 trial is based on encouraging data that were presented earlier this month at the 2008 annual meeting of the American Society of Clinical Oncology (ASCO). Safety and clinical activity data were presented from an ongoing phase 1 trial of XL184 in 69 patients with various solid tumors, including 17 response-evaluable patients with MTC. These data showed a disease control rate (percentage of patients with partial responses or prolonged stable disease >3 months) of 100% in the evaluable MTC patients, with 53% of those patients (9 of 17) experiencing partial responses. The median duration of partial responses and stable disease for patients with MTC has not been reached (range 1+ to 22+ months). Most of the MTC patients in the trial had previously failed other treatments, including tyrosine kinase inhibitors with anti-RET activity (e.g., vandetanib, sorafenib, or motesanib), chemotherapeutic agents, immunotherapy, radioactive iodine, and radiotherapy.

Several additional studies with XL184 have recently been initiated to complement the planned pivotal trial in patients with MTC as part of Exelixis' strategy to rapidly advance compounds into areas of high unmet medical need while potentially expanding into broader commercial markets by demonstrating activity in major tumor types. A phase 1/2 trial of XL184 as a single agent and in combination with erlotinib was recently initiated in patients with non- small cell lung cancer. In addition, a phase 2 study of XL184 in patients with glioblastoma multiforme is ongoing.

About 184

XL184 inhibits MET, RET, and VEGFR2, which are key drivers of tumor growth, metastasis, survival, and angiogenesis. In pharmacodynamic studies in mice, oral administration of XL184 resulted in balanced and durable inhibition of these targets. The compound has also shown activity against common mutant forms of RET and MET. XL184 has exhibited dose-dependent tumor growth inhibition and tumor regression in a variety of tumor models, including breast cancer, colon cancer, MTC, non-small cell lung cancer, and glioblastoma.

About Medullary Thyroid Cancer

The American Cancer Society estimates that MTC accounts for 5% of all thyroid cancers. MTC occurs in sporadic and inherited forms (approximately 80% and 20% of MTC, respectively). Patients with the inherited form of MTC invariably have an activating mutation in RET in their germline DNA. Activating mutations in RET are also present in the tumor DNA of up to 50% of sporadic MTC patients with no familial history of thyroid cancer. MTC may metastasize to lymph nodes or other organs before it is ever diagnosed. Additionally, MTC does not take up radioactive iodine, which is commonly used to treat other types of thyroid cancers and to diagnose metastases. As a result, MTC is more difficult to treat than other thyroid cancers. There are no approved therapies for MTC; however, common treatments for MTC include surgery to remove malignant tissue, radiation therapy, and chemotherapy, all of which are associated with potential side effects, some of which may be long-term.

About Exelixis

Exelixis, Inc. is a development-stage biotechnology company dedicated to the discovery and development of novel small molecule therapeutics for the treatment of cancer and other serious diseases. The company is leveraging its fully integrated drug discovery platform to fuel the growth of its development pipeline, which is primarily focused on cancer. Currently, Exelixis' broad product pipeline includes investigational compounds in phase 2 and phase 1 clinical development. Exelixis has established strategic corporate alliances with major pharmaceutical and biotechnology companies, including GlaxoSmithKline, Bristol-Myers Squibb, Genentech, Wyeth Pharmaceuticals, and Daiichi-Sankyo. For more information, please visit the company's website at http://www.exelixis.com.

Disclaimer

Participation by Dr. Ball and Dr. Nelkin in the development of this product as members of the Clinical Steering Committee does not constitute endorsement by the Johns Hopkins University or the Johns Hopkins Hospital and Health System.

Forward-Looking Statements

This press release contains forward-looking statements, including without limitation statements related to: the timing of the initiation and size of clinical trials for XL184; the future development and potential efficacy of XL184; and our strategy to advance compounds and expand into broader commercial markets. Words such as "plan," "expect," "will," "may" and similar expressions are intended to identify forward-looking statements. These forward-looking statements are based upon our current plans, assumptions, beliefs and expectations. Forward-looking statements involve risks and uncertainties. Our actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, risks related to the potential failure of XL184 and our other compounds to demonstrate safety and efficacy in clinical testing; the therapeutic and commercial value of XL184 and our other compounds; our ability to initiate clinical trials for XL184 at the referenced times; and our ability to enter into new collaborations, continue existing collaborations and receive milestones and royalties under our collaborative agreements. These and other risk factors are discussed under "Risk Factors" and elsewhere in our quarterly report on Form 10-Q for the quarter ended March 28, 2008, and other filings with the Securities and Exchange Commission. We expressly disclaim any duty, obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in our expectations with regard thereto or any change in events, conditions or circumstances on which any such statements are based.

Exelixis and the Exelixis logo are registered U.S. trademarks.

SOURCE Exelixis, Inc.
CONTACT: Charles Butler, Senior Director, Corporate Communications &
Investor Relations, +1-650-837-7277, cbutler@exelixis.com, or Soleil Harrison,
Senior Manager, Corporate Communications, +1-650-837-7012,
sharrison@exelixis.com, both of Exelixis, Inc.
Web site: http://www.exelixis.com