Additional value of EGFR downstream signaling phosphoprotein expression to KRAS status for response to anti-EGFR antibodies in colorectal cancer Geraldine Perkins 1,2 , Astrid Lie `vre 1,2,3 , Carole Ramacci 4,5 , Tchao Me ´atchi 3 , Aure ´lien de Reynies 6 , Jean-Franc ¸ois Emile 7,8 , Vale ´rie Boige 9 , Gorana Tomasic 9 , Jean-Baptiste Bachet 7,8 , Fre ´deric Bibeau 10 , Olivier Bouche ´ 11,12 , Fre ´de ´rique Penault-Llorca 13,14 , Jean-Louis Merlin 4 and Pierre Laurent-Puig 1,2,3 1 Institut National de la Recherche et de la Sante ´ Me ´dicale (INSERM), UMR-S775, Paris, France 2 Universite ´ Paris Descartes, Paris, France 3 Assistance Publique – Ho ˆpitaux de Paris, Ho ˆpital Europe ´en Georges Pompidou, Paris, France 4 Centre Alexis Vautrin, Nancy Universite ´, Vandoeuvre Les Nancy, France 5 Nancy Universite ´, Nancy, France 6 Programme Carte d’Identite ´ des Tumeurs (CIT), Ligue Nationale Contre le Cancer, Paris, France 7 Assistance Publique – Ho ˆpitaux de Paris, Ho ˆpital Ambroise Pare ´, Boulogne-Billancourt, France 8 Universite ´ de Versailles, Saint-Quentin-en-Yvelines, Versailles, France 9 Institut Gustave Roussy, Villejuif, France 10 Centre Val d’Aurelle Montpellier, France 11 CHU Reims, Ho ˆpital Robert Debre ´, Reims, France 12 Universite ´ Reims Champagne-Ardenne, Reims, France 13 Centre Jean Perrin, Clermont-Ferrand, France 14 Universite ´ Auvergne, Equipe Associe ´e EA4233, Clermont-Ferrand, France KRAS mutations are a strong predictive marker of resistance to anti-epidermal growth factor receptor (EGFR) antibodies in advanced colorectal cancer (CRC) but only a subset of wild-type (WT) KRAS patients are responders, suggesting the existence of additional markers of resistance to this treatment. The activation of EGFR downstream signaling pathways may be one of these ones. In a series of 42 patients with advanced CRC treated with cetuximab/panitumumab, for whom KRAS status was previously determined, we retrospectively analyzed the intratumor expression of EGFR downstream signaling phosphoproteins of the RAS/MAPK and PI3K/AKT pathways (pERK1/2, pMEK1, pAKT, pP70S6K and pGSK3b) using Bio-Plex V R phosphoprotein array. Association with tumor response, progression-free survival (PFS) and overall survival (OS) was assessed. The expression of all the phosphoproteins was higher in KRAS mutated tumors than in WT tumors. The expression of pP70S6K was lower in responders than in nonresponder patients. In univariate analysis, patients with high pMEK1 or pP70S6K expression had a shorter PFS than those with low expression. Patients with high pP70S6K expression also had a shorter OS. In multivariate analysis, PFS was shorter for patients with high pMEK1 or pP70S6K expression, independently of KRAS status, as OS for patients with high pP70S6K expression. Therefore, WT KRAS patients with high pP70S6K expression had a shorter survival than those with low expression. Our results suggest the importance of EGFR downstream signaling phosphoproteins expression in addition to KRAS status to define the subgroup of patients who will not benefit from anti-EGFR therapy. Recent progress has been made in the treatment of colorectal cancer (CRC) with the introduction of new therapies target- ing the epidermal growth factor receptor (EGFR) and the vascular endothelial growth factor. Monoclonal antibodies represent one of the most important options for the inhibi- tion of EGFR. Key words: colorectal cancer, EGFR, cetuximab, KRAS mutation, phosphoprotein, P70S6K, MEK1, survival Jean-Louis Merlin and Pierre Laurent-Puig contributed equally to this work Conflict of interest: G.P.: grant, Merck Serono; A.L.: honoraria, Merck Serono; O.B.: honoraria, Merck Serono, Amgen; J.-L.M.: research funding, Merck Serono; F.P-L.: honoraria and consult, Merck Serono, Amgen; P. L. P.: honoraria, consultant and research funding, Merck Serono Amgen and Myriad Genetics. DOI: 10.1002/ijc.25152 History: Received 28 Sep 2009; Accepted 15 Dec 2009; Online 4 Jan 2010 Correspondence to: Pierre Laurent-Puig, INSERM U775, Molecular Basis of Response to Xenobiotics, Universite ´ Paris-Descartes, UFR des Saints-Pe `res, 45 Rue des Saints-Pe `res, 75006 Paris, France, Tel: 33142862081, E-mail: pierre.laurent-puig@parisdescartes.fr Cancer Cell Biology Int. J. Cancer: 127, 1321–1331 (2010) V C 2010 UICC International Journal of Cancer IJC