This 60-year old female patient initially had KRAS wt, NRAS wt, and TP53 mt colorectal mucinous adenocarcinoma with peritoneal seeding and showed a dramatic response to cetuximab for 5 months; however, during cetuximab treatment, she was found to have peritoneal seeding (Fig. 6a). The gene discussed is KRAS; the disease is mucinous adenocarcinoma.