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PURPOSE: Mutations in K-ras and TP53 genes are common in colorectal cancer. They affect biologic behavior and might influence chemotherapy susceptibility in these tumors. We investigated whether the survival of patients with Dukes C colon cancer treated with adjuvant chemotherapy is influenced by K-ras and TP53 mutations. METHODS: Mutation screening of the hot spots of the K-ras gene and of the evolutionarily conserved regions of the TP53 gene was performed by denaturing gradient gel electrophoresis technique in formalin-fixed paraffin-embedded specimens of 55 consecutive patients with Dukes C colon cancer treated with adjuvant 5-fluorouracil-based chemotherapy. The median follow-up was 47 (range, 32-66) months. RESULTS: Alterations in the mutation hot spots of K-ras were found at codon 12 (n = 11) and 13 (n = 4) in 15 of the 55 carcinomas (27 percent). No mutation was found at codon 61. Mutations of a probably causative nature in the evolutionarily conserved regions (exons 5-8) of the TP53 gene were found in 24 tumors (44 percent). K-ras and TP53 mutations were found equally in the group with recurrent disease (7/26 (26 percent) and 12/27 (44 percent), respectively) and in the group without recurrences (8/28 (24 percent) and 12/28 (43 percent), respectively). Cancer-specific survival did not differ significantly between patients with K-ras or TP53 or both mutated and nonmutated tumors, respectively (log-rank test: K-ras, P = 0.72 and TP53, P = 0.77; K-ras and TP53, P = 0.8). Also, potentially aggressive K-ras codon 12 and 13 mutations had the same survival as tumors without these mutations (log-rank test; P = 0.73). CONCLUSIONS: Patients with K-ras or TP53 or both mutated Dukes C colon tumors have the same survival as nonmutated tumors when treated with adjuvant chemotherapy. These data suggest that mutations in K-ras or TP53 alone are not prognostic indicators in patients with Dukes C colon cancer receiving adjuvant 5-Fluorouracil-based therapy.