Heterogeneity of acquired resistance to anti-EGFR monoclonal antibodies in patients with metastatic colorectal cancer

Purpose Even if RAS-BRAF wild-type and HER2/MET negative mCRC patients frequently respond to anti-EGFR monoclonal antibodies, acquired resistance almost invariably occurs. Mechanisms of resistance to EGFR blockade include the emergence of KRAS, NRAS and EGFR extracellular domain mutations as well as HER2/MET alterations. However, these findings derive from retrospective studies that analyzed one single resistance mechanism at a time; moreover, it is still unclear how molecular heterogeneity affects clonal evolution in patients. In this work, we aimed at extensively characterizing and correlating the molecular characteristics of tissue- and blood-based data in a prospective cohort of mCRC patients who received anti-EGFR antibodies. Experimental design Twenty-two RAS-BRAF wild-type, HER2/MET negative mCRC patients progressing on anti-EGFR therapy after initial response underwent re-biopsy. Next-generation sequencing and SISH/IHC analyses were performed both on archival tumors and post-progression samples. ctDNA molecular profiles were obtained in matched tissue-plasma samples. Results RAS mutations and HER2/MET amplification were the most frequently detected resistance mechanisms in both tissue and blood sample analysis. On the other hand, BRAF and EGFR ectodomain mutations were much rarer. Patients with acquired MET amplification showed worse PFS on anti-EGFRs. We detected both intra-lesion heterogeneity, as suggested by co-occurrence of different resistance mechanisms in the same sample, and inter-lesion heterogeneity. The combined analysis of tissue and blood (ctDNA) results highlights the complexity of clonal evolution triggered by EGFR blockade. Conclusions Our results indicate that it may be extremely challenging to target the complex landscape of molecular heterogeneity associated with emergence of resistance to targeted therapies in mCRC.