Histologic transformation induced by EGFR tyrosine kinase inhibitors

Although tyrosine kinase inhibitors (TKIs) targeting Epidermal Growth Factor Receptor (EGFR) activating mutations have significantly improved outcomes in EGFR-mutant non-small cell lung cancer, resistance inevitably develops. Despite the heterogeneity of resistance mechanisms, many induce activation of MAPK signaling in the presence of EGFR-TKIs. ARAF gene amplification is identified as one such mechanism that activates MAPK signaling by directly interacting with RAS, yet its clinicopathologic characteristics remain poorly understood. We characterized five cases with ARAF amplification resistant to first- or second-generation EGFR-TKIs and screened an additional 48 re-biopsied specimens following resistance to Osimertinib. Among Osimertinib-resistant tumors, we identified four cases with ARAF amplification. Overall, these nine ARAF-amplified resistant tumors retained their original founder EGFR mutation and lacked secondary alterations. Furthermore, we identified two cases showing histologic transformation from lung adenocarcinoma to small cell lung cancer (SCLC). SCLC can be classified into four subtypes defined by transcriptional signatures driven by specific transcription factors. To estimate the subtypes of these resistant tumors, RNA sequencing analysis was performed in paired samples before and after treatment with EGFR-TKIs. Overall design: Paired samples from two cases demonstrated histologic transformation from lung adenocarcinoma to small cell lung cancer following treatment with EGFR tyrosine kinase inhibitors. Post-treatment samples also exhibited ARAF amplification. Biopsied samples were extracted RNA and sequenced. ARAF amplification was determined by copy number analysis.

尽管靶向表皮生长因子受体（Epidermal Growth Factor Receptor, EGFR）激活突变的酪氨酸激酶抑制剂（tyrosine kinase inhibitors, TKIs）已显著改善EGFR突变型非小细胞肺癌患者的预后，但耐药问题仍不可避免地发生。尽管耐药机制存在异质性，但诸多耐药机制可在EGFR-TKIs存在的情况下诱导丝裂原活化蛋白激酶（Mitogen-Activated Protein Kinase, MAPK）信号通路的激活。ARAF基因扩增被证实为其中一种通过直接与RAS结合激活MAPK信号通路的耐药机制，但其临床病理特征仍鲜为人知。本研究对5例对第一代或第二代EGFR-TKIs耐药且存在ARAF基因扩增的病例进行了特征分析，并对奥希替尼（Osimertinib）耐药后额外的48例二次活检标本进行了筛查。在奥希替尼耐药的肿瘤中，本研究共鉴定出4例存在ARAF基因扩增的病例。总体而言，这9例存在ARAF基因扩增的耐药肿瘤均保留了初始的EGFR驱动突变，且未发生继发性基因改变。此外，本研究还发现2例患者的肿瘤在治疗后发生了组织学转化，从肺腺癌转变为小细胞肺癌（Small Cell Lung Cancer, SCLC）。小细胞肺癌可根据特定转录因子驱动的转录特征分为4个亚型。为明确此类耐药肿瘤的亚型，本研究对EGFR-TKIs治疗前后的配对样本进行了RNA测序分析。研究整体设计：2例患者的配对样本显示，在接受EGFR酪氨酸激酶抑制剂治疗后，肿瘤组织学类型从肺腺癌转化为小细胞肺癌，且治疗后的样本同时存在ARAF基因扩增。对活检标本提取RNA并进行测序，通过拷贝数分析确定ARAF基因扩增状态。