Amplification of the MET receptor to drive resistance to anti-EGFR therapies in colorectal cancer.

11005 Background: The anti EGFR monoclonal antibodies cetuximab and panitumumab are used to treat metastatic colorectal cancer patients but their clinical efficacy is limited by the development of acquired resistance. We recently reported that secondary KRAS mutations are responsible for acquired resistance in approximately 50% of the patients who initially respond to cetuximab or panitumumab (Misale et al., Nature 2012; Diaz et al., Nature 2012). Here we studied the molecular bases of relapse in CRC patients who do not develop KRAS mutations during the course of anti-EGFR therapy. Methods: Next generation sequencing was applied to tumor biopsies to identify genetic alterations associated with relapse to cetuximab and panitumumab in mCRC patients. Detection and quantitation of genetic alterations in circulating tumor DNA was used to monitor the occurrence of KRAS mutations and MET amplification in blood samples. Results: Molecular analyses of tumor biopsies from patients who did not develop KRAS mutations during anti-EGFR therapy revealed high level of amplification of the MET proto-oncogene in 3/5 cases. Quantitative PCR, FISH and IHC analysis confirmed high level of MET amplification in the post-therapy samples but not in the matched pre-treatment tissues. We developed a PCR based assay to detect the presence of the MET amplicon in circulating, cell-free, DNA. We found that MET amplification could be detected in the blood as early as 3 months after initiation of anti EGFR therapy. To functionally evaluate the role of MET amplification on resistance to anti EGFR antibody therapies we exploited patient-derived CRC xenografts (‘xenopatients). We found that (2/2) xenopatients established from MET amplified tumors were completely refractory to cetuximab but showed sensitivity to the Met inhibitor crizotinib. Conclusions: Amplification of the MET proto-oncogene is responsible for acquired acquired resistance to anti-EGFR antibody therapy in a subset of CRCs. The emergence of MET amplification in circulating, cell-free, DNA may be used to select patients most likely to benefit from anti MET therapies.