Cell viability analysis suggested that in the presence of cetuximab in combination with 10 μmol/L 5-FU, compared with mock transfected cells, DiFi cells overexpressing p.K944N, p.V955G, p.V955I, p.K966E, p.E542K, p.E545K, and p.H1047R exhibited a high degree of resistance...These results demonstrate that these candidate mutations are likely to be involved in conferring resistance...

Overall, tumors harboring mutations in the KRAS-NRAS-BRAF axis responded poorly to cetuximab-based treatment….tumor A00021 had both AKT1 E17K (27.9%) and BRAF G469A (19.7%) mutations, and tumor A00026 had both BRAF D594G (26.7%) and PIK3CA E542K (15.6%) mutations....tumor A00021 had both AKT1 E17K (27.9%) and BRAF G469A (19.7%) mutations, and tumor A00026 had both BRAF D594G (26.7%) and PIK3CA E542K (15.6%) mutations....tumor A00021 had both AKT1 E17K (27.9%) and BRAF G469A (19.7%) mutations, and tumor A00026 had both BRAF D594G (26.7%) and PIK3CA E542K (15.6%) mutations. Such differences in mutant allele frequencies implies complex intra-tumor heterogeneity, which may also contribute to the lack of response to cetuximab.