The BOND-2 study randomized patients with irinotecan- and oxaliplatin-refractory but bevacizumab na?ve disease to cetuximab and bevacizumab with or without irinotecan . types of normal tissues as well as several tumor types, including CRC [2, 3]. Figure 1 illustrates the main EGFR signaling pathways described . When a ligand binds to the EGFR, the receptor forms a Cangrelor (AR-C69931) dimer resulting in a signaling cascade within the cell via tyrosine kinase activity . This signaling cascade occurs by the activation of receptor autophosphorylation which triggers a number of intracellular pathways regulating cell proliferation, prevention of apoptosis, and promotion of invasion, metastasis, and neovascularization . The proto-oncogene c-erb-B encodes the EGFR, and activation of the proto-oncogene results in EGFR expression in many tumors [7, 8]. There was therefore interest in investigating this pathway as a potential anticancer therapy target. Open in a separate window Figure 1 EGFR signaling pathway . (Reprinted with permission from American Society of Clinical Oncology 2008. All rights reserved.) Pharmacologically, there are two classes of EGFR antagonists currently in clinical use: antiEGFR monoclonal antibodies directed against the extracellular domain of the receptor and oral small-molecule EGFR TK inhibitors which block the receptor TK activity competitively . The antiEGFR monoclonal antibodies, cetuximab and panitumumab, act by binding to the extracellular region of the EGFR and therefore block the ligand-binding region which prevents ligand-induced TK activation . These monoclonal antibodies solely recognize the EGFR, making them very selective for their target . The small-molecule EGFR TK inhibitors, erlotinib and gefitinib, inhibit the catalytic activity of the TK by competing with adenosine triphosphate (ATP) to bind to the intracellular domain . These small-molecule inhibitors are not exclusive to the EGFR pathway and can block different receptor tyrosine kinases, such as the vascular endothelial growth factor (VEGF) receptor and other members of the EGFR family. Anti-EGFR monoclonal antibodies have been evaluated in both untreated metastatic CRC and chemotherapy refractory disease. Figure 2 summarizes the current treatment paradigm for metastatic colorectal cancer including the appropriate incorporation of antiEGFR monoclonal antibody therapy which improves survival for appropriately selected patients . Table 1 summarizes selected clinical trials of antiEGFR monoclonal antibodies in metastatic CRC. Response rates with single-agent antiEGFR monoclonal antibodies range from 9C12%, with much higher response rates observed when cetuximab is used in combination with chemotherapy [12C22]. When administered to unselected metastatic CRC patients, only a minority responded to EGFR inhibitor therapy. Therefore, a method to identify and predict sensitivity to these drugs was needed. Open in a separate window Figure 2 The current treatment paradigm for patients with metastatic colorectal cancer who are appropriate for intensive therapy . *For Cangrelor (AR-C69931) patients with KRAS WT gene only. CapeOX: capecitabine + oxaliplatin. Cangrelor (AR-C69931) Table 1 Clinical trials of antiEGFR monoclonal antibodies in metastatic CRC. = .013) . There was, however, no significant difference in median PFS (14 versus 26 weeks, = .055) and median OS (38 versus 50 weeks, = .051) between NRAS wild types and mutants . B-type Raf kinase (BRAF) is a component of the RAS-RAF-MEK signaling cascade of the EGFR (see Figure 1) . A specific mutation in the BRAF gene (V600E) is present in approximately 5C8% of CRCs and is thought to be limited to those tumors without mutations in exon 2 of KRAS [42, 57]. BRAF, which is located directly downstream from RAS, can have activating mutations leading to stimulation of the MEK pathway [56, 58]. BRAF mutations appear to confer a poor prognosis, and it appears that BRAF mutations also predict for a lack of response to antiEGFR monoclonal antibodies [42, 57, 59, 60]. Loupakis et al. analyzed 87 patients with KRAS WT tumors for the BRAF V600E mutation who were receiving irinotecan and cetuximab for refractory metastatic CRC. This mutation was found in 15% of the patients and was associated with a lack of KGF response to therapy (0% versus 32%, = .016) and a shorter overall survival (4.1.