Jouini Raja, Ferchichi Marwa, BenBrahim Ehsen, Ayari Imen, Khanchel Fatma, Koubaa Wafa, Saidi Olfa, Allani Riadh, Chadli-Debbiche Aschraf
Pathology Department, Habib Thameur Hospital, Tunis, Tunisia.
University of Medicine, Farhat Hached Campus, Tunis El Manar, Tunisia.
Heliyon. 2019 Mar 19;5(3):e01330. doi: 10.1016/j.heliyon.2019.e01330. eCollection 2019 Mar.
Mutations in KRAS and NRAS often result in constitutive activation of RAS in the epidermal growth factor receptor (EGFR) signaling pathway. Mutations in KRAS exon 2 (codon 12-13) predict resistance to anti-EGFR targeted therapy in patients with metastatic colorectal carcinoma (mCRC). However, it's currently known that a significant proportion of mCRC have RAS mutations outside KRAS exon 2, particularly in exons 3 and 4 of KRAS and exons 2, 3 and 4 of NRAS. No data about RAS mutations outside KRAS exon 2 are available for Tunisian mCRC. The aim of this study was to analyze RAS, using pyrosequencing, in nine hotspots mutations in Tunisian patients with mCRC.
A series of 131 mCRC was enrolled. Nine hotspots sites mutations of KRAS and NRAS were analyzed (KRAS: codons 12-13, codons 59-61, codon 117 and codon 146, NRAS: codons 12-13, codon 59, codon 61, codon 117 and codon 146) using Therascreen KRAS and RAS extension pyrosequencing kits.
Analysis was successful in 129 cases (98.5%). Mutations were observed in 97 cases (75.2%) dominated by those in KRAS exon 2 (86.6%). KRAS G12V was the most dominated mutation, observed in 25 cases (25.8%), and followed by KRAS G12S and KRAS G12D, each in 17 cases (17.5%). Mutations outside of KRAS exon 2 presented 13.4% of mutated cases and almost a third (28.8%) of KRAS exon 2 wild type mCRC. Among those, 9 cases (69.3%) carried mutations in NRAS exons 2, 3 and 4 and 4 cases (30.7%) in KRAS exons 3 and 4.
RAS mutations outside exon 2 of KRAS should be included in routine practice, since they predict also response to anti-EGFR. That would make certain these patients benefit from appropriate testing and treatment. In addition unjustified expenses of anti-EGFR targeted therapy could be avoided.
KRAS和NRAS基因的突变常常导致表皮生长因子受体（EGFR）信号通路中RAS的组成性激活。KRAS基因第2外显子（密码子12 - 13）的突变预示着转移性结直肠癌（mCRC）患者对抗EGFR靶向治疗耐药。然而，目前已知相当一部分mCRC患者的RAS突变发生在KRAS基因第2外显子之外，特别是KRAS基因的第3和第4外显子以及NRAS基因的第2、3和第4外显子。关于突尼斯mCRC患者KRAS基因第2外显子之外的RAS突变尚无数据。本研究的目的是采用焦磷酸测序法分析突尼斯mCRC患者9个热点突变位点的RAS基因。
纳入131例mCRC患者。使用Therascreen KRAS和RAS扩展焦磷酸测序试剂盒分析KRAS和NRAS基因的9个热点突变位点（KRAS：密码子12 - 13、密码子59 - 61、密码子117和密码子14；NRAS：密码子12 - 13、密码子59、密码子61、密码子117和密码子146）。
129例（98.5%）分析成功。97例（75.2%）检测到突变，以KRAS基因第2外显子的突变为主（86.6%）。KRAS G12V是最主要的突变类型，25例（25.8%）检测到，其次是KRAS G12S和KRAS G12D，各17例（17.5%）。KRAS基因第2外显子之外的突变占突变病例的13.4%，在KRAS基因第2外显子野生型mCRC中占近三分之一（28.8%）。其中，9例（69.3%）在NRAS基因的第2、3和第4外显子有突变，4例（30.7%）在KRAS基因的第3和第4外显子有突变。
KRAS基因第2外显子之外的RAS突变也应纳入常规检测，因为它们也能预测对抗EGFR治疗的反应。这将确保这些患者从适当的检测和治疗中获益。此外，还可避免抗EGFR靶向治疗的不合理费用。
