摘要目的：研究结直肠癌KRAS、NRAS及BRAF基因突变情况，分析KRAS、NRAS及BRAF基因突变在结直肠癌中的分布。方法收集2014年4月至8月于广东省人民医院首诊的200例结直肠患者的肿瘤组织，运用PCR＋直接测序的方法检测KRAS基因第2、3和4号外显子，NRAS基因第2、3和4号外显子及BRAF基因第15号外显子。结果 KRAS、NRAS、BRAF基因突变率分别为44％（88／200）、2％（4／200）和5％（10／200）。 KRAS基因突变主要集中在第2号外显子的第12和13位密码子，分别占总突变的64．8％（57／88）和12．5％（11／88），KRAS基因第3号外显子的突变主要集中在第59和61位密码子，KRAS基因第4号外显子的突变主要集中在第117和146位密码子。结论结直肠癌中KRAS基因第2号外显子突变率较高，增加检测KRAS基因位点和联合检测NRAS、BRAF基因有助于筛查出最有可能从靶向治疗中获益的结直肠癌患者。

abstractsObjective To investigate mutations frequencies of KRAS, NRAS and BRAF genes in colorectal carcinoma.Methods Tissue specimens from 200 colorectal cancer patients at diagnosis were collected and subject to KRAS,NRAS and BRAF mutation analyses by PCR-based direct DNA sequencing targeting exons 2, 3 and 4 of KRAS gene, exons 2, 3 and 4 of NRAS gene and exon 15 of BRAF gene. Results Activating mutations were detected in KRAS (44%, 88/200), NRAS (2%, 4/200) and BRAF (5%, 10/200) in this study cohort.Among KRAS mutations, 64.8% (57/88) occurred in codon 12 and 12.5%(11/88) occurred in codon 13.KRAS gene mutation in exon 3 mainly involved codons 59 and 61. KRAS gene mutation in exon 4 mainly involved codons 117 and 146.Conclusions Mutations at exon 2 of KRAS gene have the highest frequency in colorectal carcinoma.Expanding the detection sites of KRAS gene combined with NRAS and BRAF genes may help to identify patients who will most likely benefit from targeted therapies.