Background The reported prevalence of KRAS mutations, the predictive factor of efficacy of cetuximab in colorectal cancer, varies in 30–40% of patients. However, the prevalence and correlations between KRAS mutation and clinical outcome in Thai patients have never been investigated. We did a retrospective study to define the KRAS genotype in Thai patients with colorectal cancer. Methods Genomic DNA from patients’ paraffin-embedded tumour tissues was analysed for KRAS mutation at codons 12 and 13 by use of direct sequencing. Their clinical characteristics and outcomes were correlated with the genotype patterns. The concordance of KRAS genotype between primary tumour and available metastatic tumour was analysed Findings One hundred and seventeen patients with colorectal cancer were enroled. Eighty-three patients (70.9%) had wild-type KRAS (WT-KRAS) whereas 34 patients (29.1%) had mutant KRAS. Gly12Asp (GGTGAT at codon 12) was the most common mutation (41.2%). The G13D mutation was detected in 14.7% of patients. Non-hepatic metastases were associated with mutant KRAS (adjusted OR=3.699). The overall survival at 1, 2, and 5 years in patients with mutant KRAS was 85%, 75%, and 54%, respectively, compared with 96%, 83%, and 47%, respectively, in those with wild-type KRAS (p=0.56). Discordance of the KRAS genotype (wild-type primary tumours and mutant metastatic tumours) was detected in 2 of 9 patients (22.2%). After cetuximab-chemotherapy, the PFS of one case with discordant KRAS was shorter than the median PFS in 10 cases with primary WT-KRAS (2.7 months versus 12.8 months). Interpretation The prevalence of KRAS mutation in Thai patients with colorectal cancer was similar to that in other reports. Patients with mutant KRAS had more non-hepatic metastases than did those with WT-KRAS. Overall survival in patients with wild-type KRAS was not different from those with mutant KRAS. The mosaic pattern of tumour cells might account for the discordance in the KRAS status. Funding Ramathibodi cancer committee research budget. The authors declared no conflicts of interest. AOS18 Calreticulin expression is required for oral cancer-cell proliferation and migration, and is correlated with clinicopathologic features in oral squamous-cell carcinoma patients C. Wang, Y. Wu, C. Chiu, H. Kuo, C. Hsu, J. Chen Withdrawn.