Irinotecan hydrochloride (CPT-11) resistance identified by K-ras mutation in patients with progressive colon cancer after treatment with 5- fluorouracil (5-FU)

Objective: To determine the prognostic role of a K-ras mutation in tumor tissue of patients with refractory colon cancer who received irinotecan hydrochloride (CPT-11). Methods: DNA was extracted from paraffin-stored tumor tissue of 35 patients with progressive colon cancer failing treatment with 5- fluorouracil who subsequently received CPT-11 (100 mg/m² i.v. per week x 4 weeks with 2 weeks off per course). The first exon of the K-ras gene was amplified by polymerase chain reaction by using K-ras-specific primers followed by mutant enrichment sequencing. Survival differences of patients with a K-ras mutation were compared with those of patients with a normal K- ras status. Results: A total of 21 patients had a normal K-ras sequence and 14 patients had a K-ras mutation [GAT, n = 7; TGT, n = 3; and GCT, AGT, GTT, GAC (codon 13), n = 1 each]. Median survival of patients with a normal ras sequence from time of treatment with CPT-11 was 332 days compared with 169 days for patients with a K-ras mutation (p = 0.0036). No differences in age, sex, cancer stage, surgical treatment, or chemotherapy treatment were observed. Conclusion: Determination of the presence of a K-ras mutation may predict survival in patients with progressive colon cancer after treatment with 5-fluorouracil who receive CPT-11.