EGFR、PDGFRA和VEGFR2在结肠癌中的表达及变异分析

Molecular characterization of EGFR, PDGFRA and VEGFR2 in colon cancer

摘要:

目的  探讨受体酪氨酸激酶表皮生长因子受体（EGFR），血小板源性生长因子受体α多肽（PDGFRA）和血管内皮细胞生长因子受体2（VEGFR2）在30例结肠癌中的过表达及基因突变情况。方法  收集该院确诊为结肠癌的30例组织标本，免疫组织化学检测组织标本中EGFR，PDGFRA和VEGFR2表达情况，PCR-SSCP检测标本中EGFR（外显子18-21）和PDGFRA（外显子12、14和18）的基因突变情况。 结果 收集该院确诊为结肠癌的30例组织标本，免疫组织化学显示EGFR的阳性表达率为43.3%（13/30），但是EGFR热点区域（外显子18-21）未检测到激活突变。而在17例患者（56.7%）中检测到EGFR外显子20的密码子787（Q787Q）的一处无义碱基替换（CAG>CAA）。PDGFRA在所有恶性细胞中阳性表达，热点区域也未发现激活突变，但是9例标本中的12号外显子的密码子567发生CCA>CCG无义突变；4例标本中的18号外显子的密码子824发生GTC>GTT无义突变。在2例标本中还发现，14号内含子有两处碱基改变IVS14+3G>A和IVS14+49G>A，4例标本中的18号内含子存在IVS18-50insA改变。有22例（73.3%）中VEGFR2阳性表达，且VEGFR2表达与肿瘤未转移呈正相关（P =0.038）。结论  结肠癌中虽然EGFR和PDGFRA过表达，但是未检测到激活突变，而VEGR2也在结肠癌中过表达，其表达与肿瘤未发生转移有关。本研究结果为未来结肠癌治疗提供可能的方向。

Abstract:

 Objective To investigate EGFR, PDGFRA and VEGFR2 RTKs overexpression and activating gene mutations in a cohort of 30 colon cancer patients sample. Methods EGFR, PDGFRA and VEGFR2 immunohistochemistry was performed in all samples, followed by DNA isolation from the gross macroscopically dissection of the neoplastic area. Screening for EGFR (exons18-21) and PDGFRA (exons12, 14 and 18) mutations was done by PCR-single-strand conformational polymorphism (PCR-SSCP). Results Despite the presence of EGFR immunohistochemical positive reactions in 43 % (13/30) of the samples, no EGFR activating mutations in the hotspot region (exons18-21) were identified. A silent base substitution (CAG > CAA) in EGFR exon 20 at codon 787 (Q787Q) was found in 17 cases (56 %). All PDGFRA immunohistochemical reactions were positive and consistently observed in the stromal component, staining fibroblasts and endothelial cells, as well as in the cytoplasm of malignant cells. No activating PDGFRA mutations were found, yet, several silent mutations were observed, such as a base substitution in exon 12 (CCA > CCG) at codon 567 (P567P) in 9 cases and in exon18 (GTC > GTT) at codon 824 (V824V) in 4 cases. We also observed the presence of base substitutions in intron 14 (IVS14 + 3G > A and IVS14 + 49G > A) in two different cases, and in intron 18 (IVS18-50 insA) in 4 cases. VEGFR2 positivity was observed in 22 of 30 cases (73.3 %), and was significantly associated with lack of metastasis (P = 0.038). Conclusions Despite the absence of EGFR and PDGFRA activating mutations, the presence of overexpression of these three important therapeutic targets in a subset of cases may be important in predicting the sensitivity of colon cancer to specific anti-RTKs drugs.