Tumor Heterogeneity and Acquired Resistance to EGFR Inhibition

描述(由申请人提供)：越来越明显的是，癌症是一种异质性疾病，存在于单个微小克隆中的一系列突变，而这些突变在大部分肿瘤细胞中没有表现出来。总体假设是，以结直肠癌中的EGFR抑制剂为模型系统，肿瘤的异质性对治疗敏感性和获得性靶向治疗的耐受性具有重要的临床意义。更复杂的基因测序技术的引入使识别标准测序技术遗漏的低频突变成为可能。由于KRAS突变代表了一种公认的和临床使用的预测生物标志物，这为探索KRAS异质性在EGFR单抗(MAb)治疗中的意义提供了机会。最近，我们和其他人已经证明，当使用高灵敏度测序时，在大约15%的转移性结直肠癌(MCRC)患者的组织中检测到低频KRAS突变。这些罕见的KRAS突变细胞存在于通常被临床上使用的不那么敏感的护理标准检测方法识别为KRAS野生型的肿瘤中，从而导致假设这些克隆是在治疗压力下快速选择的，从而导致临床进展到治疗。回溯性的非随机数据集支持这一假设；这些低频率的KRAS突变与抗EGFR治疗的耐药性有关。具体地说，进一步选择有资格接受EGFR单抗治疗的患者将减少这种治疗对医疗保健系统的成本(考虑到25%的无反应患者的预期识别，模拟每年节省2亿美元)。在这项建议中，我们假设治疗引起的克隆性改变是异质肿瘤群体中的一种“动态平衡”。我们建议通过研究来自大型随机试验的样本，包括原发肿瘤和从患者血浆样本中获得的循环中的游离肿瘤DNA(CfDNA)来评估肿瘤遗传学变化。为了捕捉更长期的动态，我们将把这些监测技术应用于一个纵向队列，其中嵌入了一项抗EGFR再治疗的前瞻性临床试验。患者来源的小鼠异种移植模型将被用来更精确地量化肿瘤动力学。了解结直肠癌的耐药机制将需要更详细地了解基因组变化的异质性和时间动力学，从而导致改进的有益生物标记物和用先前有效的治疗方法重新挑战肿瘤的新策略。

DESCRIPTION (provided by applicant): It is increasingly apparent that cancer is a heterogeneous disease with a spectrum of mutations present in individual minor clones that aren't represented in the bulk of the tumor cells. The overall hypothesis is that tumor heterogeneity has important clinical implications for treatment sensitivity and acquired resistance to targeted therapies, using EGFR inhibitors in colorectal cancer as a model system. The introduction of more sophisticated techniques for gene sequencing has made possible the identification of low frequency mutations that were missed with standard sequencing techniques. As KRAS mutations represent a well-recognized and clinically utilized predictive biomarker, it represents an opportunity to explore the implications of KRAS heterogeneity in the setting of EGFR monoclonal antibody (mAb) therapy. Recently, we and others have shown that the presence of low frequency KRAS mutations has been detected in tissue from approximately 15% of metastatic colorectal cancer (mCRC) patients when high-sensitivity sequencing is utilized. These rare KRAS mutant cells are present in what are usually identified as KRAS wild type tumor by less sensitive standard-of-care testing methodologies currently used in the clinic, thereby leading to the hypothesis that these clones are rapidly selected under treatment pressure, resulting in clinical progression to treatment. Retrospective, nonrandomized datasets support this hypothesis; these low-frequency KRAS mutations have been correlated with resistance to anti-EGFR treatment. Specifically, further selection of patients eligible for EGFR mAb therapy would reduce the cost of such therapies to the health care system (with modeled savings of $200 million per year given the prospective identification of 25% of non-responding patients). In this proposal we hypothesize that treatment-induced clonal changes are a "dynamic balance" in a heterogeneous tumor population. We propose to evaluate tumor genetic changes by studying samples from large randomized trials, including the primary tumor and circulating free tumor DNA (cfDNA) obtained from patient plasma samples. To capture longer-term dynamics, we will apply these monitoring techniques to a longitudinal cohort with an embedded prospective clinical trial of anti-EGFR retreatment. Patient-derived murine xenograft models will be utilized to more precisely quantify tumor dynamics. Understand the mechanisms of resistance of CRC will require a more detailed understanding of the heterogeneity and temporal dynamics of genomic changes, thereby leading to improved biomarkers for benefit and novel strategies to re-challenge tumors with previously effective therapy.