Intratumor heterogeneity underlying treatment resistance in HER2+ breast tumors

 描述(申请人提供)：尽管改进了治疗策略，但对HER2靶向治疗的固有和获得性耐药性仍然很常见，并不可避免地导致疾病进展和癌症相关死亡。PIK3CA突变发生在约40%的HER2+肿瘤中，并与治疗耐药有关。为了探索HER2+肿瘤中HER2和PIK3CA突变的异质性及其在治疗耐药性中的潜在作用，我们开发了一种STAR-FISH技术(针对等位基因PCRFISH)，它允许在单细胞水平上联合检测完整组织样本中的点突变和拷贝数增加。通过在新辅助治疗前后对HER2+肿瘤应用STAR-FISH，我们发现PIK3CA突变和HER2扩增并不总是同时出现在同一个细胞中，但可以在肿瘤内的不同亚群中存在。治疗后残留肿瘤中突变的PIK3CA细胞比例较高，伴随而来的是HER2扩增细胞的相对比例降低。治疗前后样本细胞类型多样性明显不同的患者比没有改变的患者疾病特异性生存期更短。根据我们的初步数据，我们假设1)不是所有已报告发生在特定肿瘤中的体细胞突变都存在于同一肿瘤细胞中，但一些可能代表肿瘤内遗传上不同的克隆，(2)同一细胞内和同一肿瘤内的突变的组合不是随机的，而是反映了途径之间和克隆之间的合作，以及(3)同一细胞内与同一肿瘤中不同克隆中的突变的组合将产生不同的功能和临床后果。我们提出了三个具体的目标来检验这些假说：目的1.分析HER2+乳腺肿瘤的瘤内、亚克隆和细胞遗传多样性。目的2.建立和表征HER2+乳腺癌瘤内异质性的实验模型。目的3.建立数学模型来推断HER2+肿瘤在治疗过程中的演变。我们的目标是将我们的发现转化为未来的临床试验。

 DESCRIPTION (provided by applicant): Despite improved treatment strategies, inherent and acquired resistance to HER2-targeted therapies is common and inevitably lead to disease progression and cancer-related deaths. PIK3CA mutations occur in ~40% of HER2+ tumors and have been associated with resistance to treatment. To explore intratumor heterogeneity for HER2 and PIK3CA mutation in HER2+ tumors and the potential role of this in treatment resistance, we have developed a technique, STAR-FISH (Specific To Allele pcR FISH) that allows for the combined detection of point mutations and copy number gain in intact tissue samples at the single cell level. By applying STAR-FISH to HER2+ tumors before and after neoadjuvant therapy, we found that PIK3CA mutation and HER2 amplification do not always co-occur in the same cell but can be present in distinct subpopulations within tumors. Post-treatment residual tumors have higher fraction of mutant PIK3CA cells with a concomitant decrease in the relative ratio of cells with HER2 amplification. Patients with significant differene in cell type diversity between pre and post-treatment samples have shorter disease-specific survival than those with no change. Based on our preliminary data, we hypothesize that 1) not all somatic mutations that have been reported to occur in a given tumor are present in the same tumor cell but some may represent genetically divergent clones within tumors, (2) the combination of mutations within the same cell and within the same tumor is not random, but reflect cooperation among pathways and among clones, and (3) the presence of a combination of mutations within the same cell versus in different clones in the same tumor will have different functional and clinical consequences. We propose three specific aims to test these hypotheses: Aim 1. Analyze intratumor subclonal and cellular genetic diversity in HER2+ breast tumors. Aim 2. Develop and characterize experimental models of intratumor heterogeneity in HER2+ breast cancer. Aim 3. Develop mathematical models to infer the evolution of HER2+ tumors during treatment. Our goal is to translate our findings into future clinical trials.