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，在个体小克隆中存在一系列突变，这些突变在大部分肿瘤细胞中不存在。总体假设是，肿瘤异质性对靶向治疗的治疗敏感性和获得性耐药具有重要的临床意义，使用结直肠癌中的EGFR抑制剂作为模型系统。引入更复杂的基因测序技术使得鉴定标准测序技术所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性生物标志物，因此它代表了探索KRAS异质性在EGFR单克隆抗体（mAb）治疗背景下的意义的机会。最近，我们和其他人已经表明，当使用高灵敏度测序时，在约15%的转移性结直肠癌（mCRC）患者的组织中检测到低频KRAS突变的存在。这些罕见的KRAS突变细胞存在于通常通过目前临床上使用的不太敏感的标准护理测试方法鉴定为KRAS野生型肿瘤的肿瘤中，从而导致这些克隆在治疗压力下被快速选择的假设，导致临床进展到治疗。回顾性、非随机数据集支持这一假设;这些低频KRAS突变与抗EGFR治疗耐药相关。具体而言，进一步选择符合EGFR mAb治疗条件的患者将降低医疗保健系统的此类治疗成本（考虑到前瞻性识别25%的无应答患者，每年可节省2亿美元）。在这个提议中，我们假设治疗诱导的克隆变化是异质性肿瘤群体中的“动态平衡”。我们建议通过研究来自大型随机试验的样本来评估肿瘤遗传变化，包括原发性肿瘤和从患者血浆样本中获得的循环游离肿瘤DNA（cfDNA）。为了捕获长期动态，我们将这些监测技术应用于一个纵向队列，其中包含一项抗EGFR再治疗的嵌入式前瞻性临床试验。将利用患者来源的鼠异种移植物模型来更精确地量化肿瘤动力学。了解CRC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态，从而导致改善生物标志物的益处和新的策略，以重新挑战肿瘤与以前有效的治疗。

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.