Department of Genome Biology, Kinki University School of Medicine, Osaka, Japan.
J Thorac Oncol. 2012 Nov;7(11):1640-4. doi: 10.1097/JTO.0b013e3182653d7f.
Approximately 50% of lung cancer patients with epidermal growth factor receptor (EGFR)-mutations (deletion in exon 19 or L858R) who develop acquired resistance to EGFR tyrosine kinase inhibitors (TKIs) reportedly carry a secondary EGFR T790M mutation. This mutation has been suggested to be present in tumor cells before EGFR-TKI treatment in a small population of individuals. Here, we use a highly sensitive colony hybridization technique in an attempt to evaluate the actual incidence of T790M in pretreatment tumor specimens.
DNA was extracted from surgically resected tumor tissues of 38 patients with the EGFR mutation and examined for the presence of T790M, using a standard polymerase chain reaction based method followed by a modified colony hybridization (CH) technique with an analytical sensitivity of approximately 0.01%. Associations between the T790M status and clinical characteristics including time to treatment failure (TTF) for EGFR-TKI were evaluated.
The T790M mutation analysis of the specimens from the 38 patients detected 30 mutants (79%). The median TTF was 9 months for the patients with pretreatment T790M and 7 months for the patients without the T790M mutation (p = 0.44). When the patients with T790M were divided into strongly positive and modestly positive subgroups in terms of the frequency of positive signals observed using CH technique, the 7 patients with strong positivity had a TTF that was significantly longer than that of the 8 patients without T790M (p = 0.0097) and of the 23 patients with modest positivity (p = 0.0019).
Our highly sensitive CH method showed that a subgroup of non-small-cell lung cancer patients with the EGFR mutation harbored the rare T790M allele before EGFR-TKI treatment. A high proportion of T790M allele may define a clinical subset with a relatively favorable prognosis.
约 50%的表皮生长因子受体（EGFR）突变（外显子 19 缺失或 L858R）的肺癌患者在对 EGFR 酪氨酸激酶抑制剂（TKI）产生获得性耐药后，据报道携带继发性 EGFR T790M 突变。有人认为，在一小部分个体中，这种突变在 EGFR-TKI 治疗前就存在于肿瘤细胞中。在这里，我们使用一种高度敏感的集落杂交技术，试图评估预处理肿瘤标本中 T790M 的实际发生率。
从 38 名 EGFR 突变的手术切除肿瘤组织中提取 DNA，使用基于聚合酶链反应的标准方法，然后使用改良的集落杂交（CH）技术进行分析，其分析灵敏度约为 0.01%。评估 T790M 状态与包括 EGFR-TKI 治疗失败时间（TTF）在内的临床特征之间的关系。
对 38 例患者标本的 T790M 突变分析检测到 30 个突变体（79%）。T790M 预处理的患者中位 TTF 为 9 个月，无 T790M 突变的患者为 7 个月（p = 0.44）。当根据 CH 技术观察到的阳性信号频率将 T790M 患者分为强阳性和中度阳性亚组时，7 例强阳性患者的 TTF 明显长于无 T790M 的 8 例患者（p = 0.0097）和 23 例中度阳性患者（p = 0.0019）。
我们的高度敏感 CH 方法表明，一小部分 EGFR 突变的非小细胞肺癌患者在 EGFR-TKI 治疗前就携带有罕见的 T790M 等位基因。T790M 等位基因的高比例可能定义了具有相对有利预后的临床亚组。
