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...In patients without treatment benefit (n = 13), four BRAF p.V600E mutations and one rare KRAS p.G60D mutation were detected in tumor tissue...Eight of 13 (61.5%) patients without clinical benefit had a RAS/BRAF mutation versus one out of 21 (4.8%) patients with clinical benefit (P = 0.001). PFS was shorter for patients with RAS/BRAF mutations, with a median PFS of 1.8 months versus 4.9 months in wild‐type patients...