In a group of 148 stage II-III rectal cancer patients undergoing KRAS and TP53 genotyping on pretreatment tumor biopsies, they demonstrated that patients with KRAS mutated tumors had a decreased chance to get a pathological complete response compared to wildtype KRAS tumors, and specifically, no tumor with a KRAS mutation in codon 13 had a complete response. The gene discussed is KRAS; the disease is rectal cancer.