ENU mutagenesis identifies clinically relevant mutations and pathways. (A) The pathway most significantly enriched with mutations, “Signaling to P38 via RIT and RIN,” contains many of the key genes of the canonical MAP kinase pathway, and those are mutated in a mutually exclusive manner. Here, we show those genes mutated in at least three individual clones. Whole-exome sequence from 72 Cetuximab resistant ENU clones was used to identify pathways using the SLAPenrich algorithm. Amino acid substitutions are labeled for the subset of genes most frequently mutated in the pathway and/or demonstrating mutual exclusivity with other mutations. (B) Cetuximab resistance mutations. Frequency of likely ENU-derived drug resistance mutations across 42 resistant clones. The amino acid consequence of each mutation is indicated with the gene name. (C) A visual representation of the all mutated genes that comprise the “Signaling to P38 via RIT and RIN” pathway, indicating gene–gene interactions and the hierarchy of signaling. Only those genes mutated in at least three clones were taken forward for validation.