KRAS, BRAF and PIK3CA mutations in human colorectal cancer: relationship with metastatic colorectal cancer.

Many abnormal gene expressions and dysregulated signaling pathways have been found in human colorectal cancer. Activating mutations of the KRAS, BRAF or PIK3CA oncogenes are frequently found in colorectal cancer. The aim of the study was to investigate the molecular occurrence of KRAS, BRAF and PIK3CA mutations in the colorectal tumorigenesis and to study the association of these events with clinicopathological parameters. In our study, DNA was extracted from 200 cases of human colorectal cancer tissue samples. KRAS, BRAF and PIK3CA mutation analysis was performed by PCR and pyrosequencing. Using statistical methods, we analyzed the relationships between the gene mutations and clinicopathological parameters. KRAS point mutations were detected in 63/200 patients (31.5%), with codon 12 mutations in 52/200 patients (26%), codon 13 mutations in 10/200 patients (5%) and codon 12.13 bi-mutations in 1/200 patients (0.5%). The V600E mutations of BRAF were detected in 14/200 patients (7%). PIK3CA point mutations (exon 9, exon 20) were detected in 25/200 (12.5%) patients, exon 9 mutatons in 12/200 patients (6%) and exon 20 mutations in 13/200 (6.5%). Our study suggested that both KRAS and BRAF mutations are exclusive, but KRAS and PIK3CA mutations are coexistent. The mutational status of BRAF did not correlate with Dukes' staging, histological type, age and gender. However, strong associations were found between KRAS, PIK3CA mutations and Dukes' staging (staging D, 12/25, 48%). Notably, our data indicated that colorectal cancers with KRAS and PIK3CA bi-mutations are more likely to develop into liver metastasis.