Pharmacokinetic analyses indicate that the half-life of XL184 wasapproximately 100 hours (range 59-136 hours), with exposure at the MTDexceeding that required for efficacy in preclinical models. Pharmacodynamicanalyses demonstrated statistically significant changes at the MTD in plasmamarkers including VEGF-A, PlGF, and soluble VEGFR2, similar to the effects ofother anti-angiogenic agents, and consistent with the anti-VEGFR activity ofXL184. In addition, decreases in soluble MET were measured in 4 of 7 patientsat the MTD who were analyzed for this endpoint.

'We believe the results for XL184 are remarkable and strongly support ourplan to initiate a pivotal trial this summer in patients with MTC. Based onthese data, we believe that XL184 is in a strong position to become thebest-in-class therapy in MTC,' said Michael M. Morrissey, PhD, President ofResearch and Development at Exelixis. 'Given the potent activity of XL184against MET, RET, and VEGFR2, and the observed long-lasting diseasestabilization in a variety of tumor types in this phase 1 trial, we willcontinue to explore the compound's utility as a single agent, or incombination with other therapies, in tumor types like lung cancer,glioblastoma, and potentially many others.'

Investor and Analyst Briefing at ASCO, Monday, June 2, 6 pm

Exelixis will host an investor and analyst briefing on Monday, June 2, at6:00 p.m. at the Hyatt McCormick Place (Regency C&D - 2nd Floor). At thisevent, Exelixis will provide a review of its data presented at ASCO anddescribe additional data on XL147, a PI3K inhibitor, and XL281, an inhibitorof RAF. The event will be webcast and may be accessed in the Event Calendarpage under Investors at www.exelixis.com. An archived replay of this webcastwill be available until 9:00 p.m. PT/12:00 a.m. ET on July 2, 2008. Accessnumbers for this replay are: 1-888-286-8010 (domestic) and +1-617-801-6888(international); the replay passcode is: 42662164.

About XL184

XL184 inhibits MET, RET, and VEGFR2, which are key drivers of tumorgrowth, metastasis, survival, and angiogenesis. In pharmacodynamic studies inmice, oral administration of XL184 resulted in balanced and durable inhibitionof these targets. The compound has also shown activity against common mutantforms of RET and MET. XL184 has exhibited dose-dependent tumor growthinhibition and tumor regression in a variety of tumor models, including breastcancer, colon cancer, MTC, non-small cell lung cancer, and glioblastoma. Apivotal phase 3 trial of XL184 in patients with MTC is planned to begin in thesummer of 2008. Phase 1/2 and 2 studies of XL184 in non-small cell lung cancerand glioblastoma multiforme are ongoing.

About Medullary Thyroid Cancer

The American Cancer Society estimates that MTC accounts for 5% of allthyroid cancers.