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EXELIXIS BEGINS PHASE II TRIAL OF GASTRIC CANCER DRUG

December 27, 2006

Exelixis Dec. 22 announced the initiation of a Phase II clinical trial of XL880 in patients with gastric cancer. As previously announced, a Phase II trial of XL880 in patients with papillary renal cell carcinoma was initiated in June 2006. XL880 is an orally bioavailable small molecule inhibitor of the MET and VEGF receptor tyrosine kinases (RTKs) that are involved in tumor cell growth, migration and angiogenesis.

The multi-center open-label Phase II study will be conducted at multiple clinical sites and enroll patients with metastatic, poorly differentiated diffuse gastric cancer, a tumor type that is associated with amplification of the MET gene. The primary objectives of the study are to determine best- confirmed response rate and to evaluate safety and tolerability of XL880 administered orally for five consecutive days every two weeks. Secondary objectives are to assess progression-free survival, overall survival and duration of response, and to continue characterizing the pharmacokinetic and pharmacodynamic profiles of XL880.

Data from a Phase I trial of XL880 were presented most recently in November 2006 at the EORTC-NCI-AACR Symposium on Molecular Targets and Cancer Therapeutics. As of October 6, 2006, 40 patients had been enrolled in the Phase I trial and were evaluable for safety; 29 of these were also evaluated for XL880 pharmacokinetics. As reported by the investigators, four patients have had partial responses; four patients have had minimal responses; and seven patients have had stable disease for three to seven months.

Additionally, analysis of biopsy samples taken from a patient with melanoma who had stable disease indicated that XL880 inhibited the activation of the RTKs MET and RON, decreasing the activity of the downstream proteins ERK and AKT, which translated into an overall decrease in tumor cell proliferation and an increase in apoptosis in the tumor sample. Similar results have also been observed in tumor biopsies from patients with metastatic breast cancer and medullary thyroid carcinoma. These changes were not observed in samples of normal tissue taken from the same patient.