Encouraging Interim Data From a Phase 2 Trial of XL647

[Christine]

**Clinical benefit observed in over 60% of evaluable patients**

SEOUL, South Korea, Sept. 4 -- Exelixis, Inc. today reported interim data from an ongoing phase 2 trial evaluating XL647 as first-line therapy for patients with non-small cell lung cancer (NSCLC). This open-label phase 2 trial is ongoing in previously untreated patients with stage IIIB or IV NSCLC who have adenocarcinoma histology and meet one of the following three criteria: Asian descent, female gender, or no or minimal smoking history. XL647 is administered orally, at a dose of 350 mg on Days 1-5 of repeated 14-day cycles.

To date, over 60% of evaluable patients in the phase 2 study have had partial responses (PR) or stable disease (SD) as their best response. Importantly, responses have been observed in patients with and without activating mutations in the epidermal growth factor receptor (EGFR), a target of XL647. Activating mutations in EGFR have been associated with improved sensitivity to other EGFR inhibitors. Dr. Shirish Gadgeel of Karmanos Cancer Institute at Wayne State University presented the data today in a poster (Abstract P3-136) at the 12th International Association for the Study of Lung Cancer World Conference on Lung Cancer, which is being held in Seoul, South Korea.

Key data points reported by Investigators:

-- XL647 has demonstrated anti-tumor activity in patients with previously untreated NSCLC: >60% of evaluable patients experienced clinical benefit as their best response (8 PR and 11 SD out of 30 evaluable patients).

-- Of the 8 patients who experienced partial responses, 4 had EGFR exon 19 deletions, 1 had an EGFR L858R mutation, and 3 were EGFR wild-type.

-- All 6 patients with EGFR-activating mutations demonstrated clinical benefit (5 PR, 1 SD).

-- XL647 is generally well tolerated in this patient population. The most frequently reported adverse events assessed as being related to XL647 were diarrhea, rash, fatigue, and nausea, all of which were Grade 1 or Grade 2 in severity.

"The data reported today demonstrate that XL647 has potential utility in patient populations with both mutated and wild-type EGFR," said Dr. Shirish Gadgeel of Karmanos Cancer Institute at Wayne State University. "Importantly, the data highlight that patients to date appear to have milder EGFR-related side-effects -- rash and diarrhea -- than previously described with other EGFR inhibitors while retaining potent anti-tumor activity with durable responses and stable disease. Although these are early results, they provide a compelling rationale for expediting the full development of XL647 in non-small cell lung cancer."

"These data suggest that XL647 has the potential for utility in patients with NSCLC who have an activating EGFR mutation and those with wild-type EGFRs. We believe these data support an aggressive clinical development strategy in first, second and third-line treatment as both a single agent and in combination with other therapies," said George A. Scangos, Ph.D., president and chief executive officer of Exelixis. "Moreover, new data from an ongoing phase 1 trial of XL647 suggest that daily dosing results in higher drug concentrations than those observed to date in this phase 2 study with intermittent dosing. We expect to complete this evaluation of both daily and intermittent dosing schedules soon in order to select the optimal regimen and dose for the late-stage development of XL647."

The most frequently reported treatment-related adverse events (AEs) were Grade 1 and 2 diarrhea and fatigue, and Grade 1 nausea and rash. Six patients have had a maximum Grade 1 QTc interval prolongation, and 7 patients a maximum Grade 2; the increases were clinically asymptomatic and not associated with AEs or dose reduction or delay. One patient who experienced an event of asymptomatic Grade 3 QTc interval prolongation had ineligible baseline QTc values (Grade 2) and was withdrawn from the study. A total of 16 serious AEs were reported in 8 patients. 5 events in 4 patients were considered possibly or probably related to study drug: Grade 3 GI hemorrhage and duodenal ulcer in 1 patient, and Grade 3 pneumonia, Grade 4 pulmonary embolism, and Grade 2 haemoptysis.

About XL647

XL647 is a potent inhibitor of receptor tyrosine kinases (RTKs) that are implicated in driving tumor proliferation and vascularization (blood vessel formation). XL647 inhibits EGFR, HER2 and VEGFR2. The compound has been optimized for high potency and oral bioavailability (using in vivo systems), demonstrates excellent activity in target-specific cellular functional assays and has shown sustained inhibition of target RTKs preclinically in vivo following a single oral dose. Two phase 2 trials in patients with NSCLC are ongoing.

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 for cancer and renal disease. Exelixis has established strategic corporate alliances with major pharmaceutical and biotechnology companies, including GlaxoSmithKline, Bristol-Myers Squibb Company, Genentech, Wyeth Pharmaceuticals and Daiichi-Sankyo. For more information, please visit the company's web site at http://www.exelixis.com.