e14033 Background: Recent evidence highlights the potential prognostic and predictive value of BRAF and K-RAS gene alterations in patients with colorectal cancer. To determine whether differences exist in the molecular mechanisms driving colorectal cancer between Japanese and Western, we characterized Japanese patients with colorectal cancer by assessing genetic alterations involved in cancer progression and response to treatment. Methods: We retrospectively evaluated 254 Japanese diagnosed with colorectal cancer at our institution between 1994 and 2009. Mutations in KRAS codons 12 and 13 and BRAF codon 600 were identified by direct sequencing. Microsatellite instability (MSI) status was determined by genotyping in the 5 loci. Associations between KRAS or BRAF mutation and clinicopathological characteristics and prognosis were evaluated. Results: KRAS and BRAF mutation were detected in 33.5% and 6.7% of all patients, respectively. KRAS mutation was correlated with poor recurrence free survival (RFS) (p = 0.03), especially in stage II patients (p = 0.007). BRAF mutation was significantly correlated with the anatomical site of tumor (p < 0.001), tumor grade (p = 0.001) and high frequency of microsatellite instability (p < 0.001). BRAF mutation was also correlated with poor overall survival in all cases of patients (p = 0.009). Overall, the background of KRAS and BRAF mutation was almost similar between CRCs of Western countries and those of Japanese. However, KRAS mutation status was considered to be helpful to predict recurrence in Japanese patients with stage II CRC. Conclusions: Our findings indicate that BRAF and K-RAS mutation plays an important role in the tumorigenesis of colorectal cancer. These results indicate that molecular analysis for BRAF and K-RAS may be a useful biomarker for identifying patients with right-sided colon cancer with poor outcome who may benefit from a more individualized course of therapy.
Microsatellite instability has a positive prognostic impact on stage II colorectal cancer after complete resection: results from a large, consecutive Norwegian series