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7568 Background: FDG-PET could be useful for early evaluation of tumor response to tyrosine kinase inhibitors (TKI). Glucose metabolic activity seems to closely reflect response to epidermal growth factor receptor (EGFR) TKI in vivo and in vitro (Su H et al, Clin Cancer Res 2006;12:5659–67). Thus, we attempted to assess the clinical value of FDG-PET for early prediction of tumor response to Eb an EGFR-TKI. Methods: Pts with NSCLC stage IV in progression after at least one line of chemotherapy and PS 0–1 were treated with Eb (150 mg orally once daily). FDG-PET was performed on days 0 and 2, after administration of 3 daily doses. FDG uptake was evaluated as the maximum standardized uptake value in the tumor (SUVmax). SUVmax was divided by SUV of the background region (liver) to produce the tumor:nontumor ratio (TNT). FDG-PET responses were evaluated by quantitative changes on TNT and classified according to the EORTC PET study group. PET response were compared with radiographic tumor response (RECIST criteria) assessment based on CT scan at baseline and on day 45. Results: From May 2007, 27 pts were enrolled and 23 were evaluable (4 not-evaluable: 2 BAC PET negative, 2 violations). FDG-PET revealed a metabolic partial response (PR) in 8 pts; subsequent CT scan assessment evidenced 4 PR and 4 long lasting stable disease (SD), respectively. Seven pts had metabolic progressive disease (PD) at PET scan and 8 had SD, all of them presented PD at CT scan. Metabolic PR was associated with a longer median progression-free survival (152 vs 45 days, p = < 0.0001) and longer overall survival (323 vs 128 days p=0.15). For radiological PD pts who presented metabolic SD or PD, survival time was respectively 220 and 117 days. EGFR gene mutation, gene copy number and protein expression are ongoing. Conclusions: FDG-PET using changes on TNT can very early predict (already 2 days after initiation) Eb treatment outcome. Particularly, pts with early metabolic PD are unlikely to benefit from Eb. Therefore, evaluation of the early metabolic response holds promise for assessment of pts selection. The two different behavior of FDG-PET observed on refractory pts, deserve biomolecular analysis for understanding mechanism of resistance. No significant financial relationships to disclose.