Background: Cyclooxygenase-2 (COX-2)-dependent signalling represents a potential mechanism of resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) therapy in NSCLC. This is mediated in part through an EGFR-independent activation of MAPK/Erk by the COX-2 metabolite PGE2. In addition, PGE2 promotes downregulation of E-cadherin and epithelial to mesenchymal transition. We hypothesize that EGFR and COX-2 inhibition with E and HD-C will augment EGFR TKI efficacy by increasing tumor E-cadherin expression and blocking PGE2-mediated resistance to EGFR inhibition. Methods: Pts with stage IIIB/IV NSCLC who progressed following at least one line of therapy or refused standard chemotherapy were randomized to E (150mg/day)/HD-C (600mg/2x day) vs E/P in a 28-day cycle. Pts were stratified by smoking status and ECOG PS. The primary endpoint was PFS with 80% power to detect a 50% improvement; assessments were performed every 2 cycles. Secondary endpoints included response rate, OS and evaluation of molecular markers in tissue and serum to assess targeting COX-2-related pathways and evaluate EGFR TKI-resistance. All pts were required to have pre-treatment tissue available. Results: 107 pts were enrolled with comparable baseline characteristics in both arms. Disease control rate (DCR) was similar in both arms, and a trend toward improved PFS was seen in the E/HD-C arm with HR 0.81 (see Table). Analysis of those with EGFR wild type revealed a significantly increased PFS while those with EGFR mutation had similar PFS in both groups. Safety analysis showed similar toxicity in both arms. Additional biomarker correlations will be presented. Conclusions: The combination of E/C in metastatic NSCLC with HD-C is well tolerated and demonstrates significantly improved efficacy in EGFR wt population. This warrants further study into the COX-2-dependent mechanisms of primary resistance to EGFR TKI therapy. Supported by NIH 1P50 CA90388, K12 CA01727 and medical research funds from the Dept of Veterans’ Affairs.

	E/HD-C (n=54)	E/P (n=53)	p value
PFS (mo)	5.4	2.9	0.31
PFS (EGFR mut, mo)	10.8	9.2	0.73
PFS (EGFR wt, mo)	3.6	1.8	0.045
PFS (EGFR na, mo)	2.7	2.7	0.96
DCR (%)	59	55	0.70