Chen Jing, Guo Fang, Shi Xin, Zhang Lihua, Zhang Aifeng, Jin Hui, He Youji
Department of Pathogenic Biology and Immunology, Medical School of Southeast University, 87 Dingjiaoqiao, Nanjing 210009, Jiangsu, China.
BMC Cancer. 2014 Nov 3;14:802. doi: 10.1186/1471-2407-14-802.
Mutations in KRAS, BRAF and PIK3CA are the most common somatic alterations found in the colorectal cancer (CRC) patients from Western countries; but their prevalence and prognostic value have not been adequately assessed in Asian patients. The aim of this study was to determine the mutation frequencies of these genes in Chinese CRC patients and to investigate their impact on prognosis.
The sequences of exon 2 of KRAS, exon 15 of BRAF and exons 9 and 20 of PIK3CA were evaluated by PCR and direct sequencing using DNA extracted from formalin-fixed paraffin-embedded (FFPE) tissues from primary CRC tumors of 214 patients (colon/rectum: 126/88).
KRAS, BRAF and PIK3CA mutations were identified in 44.9% (96/214), 4.2% (9/214) and 12.3% (26/212) CRCs, respectively. The most frequent mutations in KRAS, BRAF and PIK3CA were G12D, V600E and H1047R, respectively. All BRAF and 80.8% PIK3CA mutations were from colon cancer patients. BRAF V600E was associated with advanced TNM (P < 0.001), more distant metastases (P = 0.025), and worse overall survival (OS, P < 0.001; multivariate HR = 4.2, P = 0.004) in colon cancer patients. Compared with KRAS wt/BRAF wt CRC patients (N = 109), those with KRAS codon 13 mutations (N = 25) had significantly worse OS (P = 0.016; multivariate HR = 2.7, P = 0.011), whereas KRAS codon 12-mutated cases were not significantly associated with survival. Among the three most common KRAS mutations, G13D (N = 23) showed significant association with poor OS (P = 0.024; multivariate HR = 2.6, P = 0.016) compared with KRAS wt/BRAF wt patients.
Our findings indicate that PI3K/RAS-RAF signaling pathway genes are frequently mutated in Chinese CRC patients, but have different characteristics than found in Western patients. BRAF V600E is an independent prognostic factor for Chinese patients. Our finding that KRAS codon 13 mutations (in particular G13D) are associated with inferior survival in BRAF wild-type CRCs in Chinese patients was not reported thus far. Our data emphasizes the importance of prospective evaluation of molecular features in CRC patients, because a single mutation type may represent a distinct biologic effect and clinical implication.
KRAS、BRAF和PIK3CA基因的突变是西方国家结直肠癌（CRC）患者中最常见的体细胞改变；但在亚洲患者中，它们的发生率和预后价值尚未得到充分评估。本研究的目的是确定这些基因在中国CRC患者中的突变频率，并研究它们对预后的影响。
采用聚合酶链反应（PCR）和直接测序法，对214例原发性CRC肿瘤（结肠/直肠：126/88）的福尔马林固定石蜡包埋（FFPE）组织提取的DNA进行KRAS基因第2外显子、BRAF基因第15外显子以及PIK3CA基因第9和20外显子序列评估。
KRAS、BRAF和PIK3CA基因的突变分别在44.9%（96/214）、4.2%（9/214）和12.3%（26/212）的CRC患者中被检测到。KRAS、BRAF和PIK3CA基因最常见的突变分别为G12D、V600E和H1047R。所有BRAF和80.8%的PIK3CA基因突变均来自结肠癌患者。BRAF V600E与结肠癌患者的晚期TNM分期（P＜0.001）、更多远处转移（P = 0.025）以及更差的总生存期（OS，P＜0.001；多变量风险比HR = 4.2，P = 0.004）相关。与KRAS野生型/BRAF野生型CRC患者（N = 109）相比，KRAS密码子13突变的患者（N = 25）的OS明显更差（P = 0.016；多变量HR = 2.7，P = 0.011），而KRAS密码子12突变的病例与生存率无显著相关性。在三种最常见的KRAS突变中，与KRAS野生型/BRAF野生型患者相比，G13D（N = 23）与较差的OS显著相关（P = 0.024；多变量HR = 2.6，P = 0.016）。
我们的研究结果表明，PI3K/RAS-RAF信号通路基因在中国CRC患者中经常发生突变，但具有与西方患者不同的特征。BRAF V600E是中国患者的一个独立预后因素。我们发现KRAS密码子13突变（特别是G13D）与中国BRAF野生型CRC患者较差的生存率相关，这一发现迄今尚未见报道。我们的数据强调了对CRC患者分子特征进行前瞻性评估的重要性，因为单一突变类型可能代表不同的生物学效应和临床意义。
