Baseline mutations in genes: BRAF, KRAS, NRAS. Mutations detected in tumor tissue during routine work‐up and in cfDNA prior to start of cetuximab monotherapy...Our analysis of patients’ baseline ctDNA revealed three additional patients who had KRAS mutations (KRAS p.G12A, p.G61H, and a combination of the two) that had not been detected in tumor tissue...While almost all patients with additional KRAS or BRAF mutations were resistant to therapy, we also had one patient with clinical benefit who nevertheless had a polyclonal KRAS mutation (p.G61H and p.G12A) in ctDNA...