Clinical significance of K-ras and BRAF mutations in Chinese colorectal cancer patients.

AIM: To identify and assess mutations in the K-ras and BRAF genes in a cohort of Chinese patients with colorectal cancer (CRC) for their association with various clinicopathological parameters and prognosis. METHODS: Genomic DNA was isolated from frozen tissues. Pyrosequencing analysis was conducted to detect mutations in the K-ras (codons 12, 13, and 61) and BRAF genes (codon 600). Statistical analysis was carried out using SPSS-15.0 software. RESULTS: Among the 118 colorectal cancer patients, we detected 41 (34.7%) mutations in the K-ras gene. Mutation frequencies at codon 12 and codon 13 were 23.7% (28/118) and 10.2% (12/118), respectively. Only one patient harbored a point mutation at codon 61 (0.8%, 1/118). Gender was the only factor that showed an obvious relationship with K-ras gene mutation (female 44.7% vs male 28.2%, P = 0.037). Other clinicopathological features, such as age, location of the tumor, tumor differentiation, Tumor, Node and Metastases classification, and the Union for International Cancer Control staging, showed no positive relationship with K-ras gene mutations. No significant correlation was observed between the presence of K-ras mutations (codons 12, 13, and 61) and the survival of the patients. BRAF mutations were rare, and only two patients (1.7%) harbored a detectable mutation at codon 600. CONCLUSION: K-ras gene mutation is a common event in our 118 Chinese CRC patients, with an obvious relationship with gender. However, it seems not to be an independent prognostic factor in CRC patients. The BRAF gene is rarely mutated in Chinese CRC patients.

[K-ras gene mutation in colorectal cancer and its clinicopathologic significance].

OBJECTIVE: To establish a simple, rapid and economical method in detecting mutations of oncogene K-ras and to investigate its mutations in colorectal cancer tissues and its relationship with clinicopathologic characteristics of colorectal carcinoma. METHODS: Forty colorectal cancer tissues were tested for K-ras mutations at codon 12 and codon 13 using polymerase chain reaction (PCR) followed by direct sequencing and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) followed by sequence analysis. The other 113 colorectal cancer tissues were tested for K-ras mutations at codon 12 and codon 13 using PCR-RFLP followed by sequence analysis only. The mutation results were analyzed with the corresponding clinical pathological data. RESULTS: Among 40 colorectal cancer cases, none of K-ras mutations at codon 12 and codon 13 was detected by PCR followed by direct sequencing. However, K-ras mutations were found in 11 cases (11/40, 27.5%) by PCR-RFLP followed by sequence analysis, including 8 cases at codon 12 and 3 cases at codon 13 respectively. Among 153 colorectal cancer cases, point mutations were detected by PCR-RFLP followed by sequence analysis in 58 cases (37.9%). Point mutations at codon 12 were found in 46 cases and 12 cases at codon 13. Mutations with the highest frequency were G→A transitions (25/58, 43.1%) at codon 12. No significant correlation was observed between mutations of K-ras and gender, invasive depth, tumor differentiation, number of invaded lymph nodes, distant metastasis and clinical stage (P > 0.05). Mutation of oncogene K-ras at codon 12 and codon 13 was closely related with age and tumor location (P < 0.05). The incidence of K-ras mutation was significantly higher in younger patients and in patients with ascending colon cancer. CONCLUSIONS: PCR-RFLP followed by sequence analysis is a rapid, simple, sensitive and low-cost method. It is a suitable technology for detecting hot-spot mutations in the K-ras oncogene. Mutation of oncogene K-ras at codon 12 and codon 13 is a common molecular event in colorectal carcinogenesis, which might be related with age and tumor location.