Abstract 1505: Targeted sequencing for the assessment of intratumor heterogeneity
Authors: Izumchenko Eugene G. , Chang Xiaofei , Brait Mariana , Westra William , Sidransky David 
Published: May 2015

Abstract
Adenocarcinoma, the most common subtype of lung cancer, is notorious for eluding early detection. Thus, understanding the early steps of lung tumorigenesis at the genetic level might facilitate the development of more effective strategies for the prevention, early diagnosis, and treatment of lung cancer. Nearly 10% of lungs resected for adenocarcinomas harbored minute discrete foci of cytologically atypical bronchiolalveolar cells that are designated as atypical adenomatous hyperplasia (AAH). It has been postulated that these lesions represent an early stage in glandular neoplasia, which is now viewed as a progression from AAH to adenocarcinoma in situ (AIS) to minimally invasive adenocarcinoma (MIA), although, the biological nature of AAH is poorly understood and very controversial. To delineate tumor clonal heterogeneity as a function of tumor progression in early NSCLC neoplasias, we isolated DNA from different zones of histologic progression within the same lesion and performed targeted next generation sequencing which targets a panel of 134 well-characterized cancer and pharmacogenomics genes. We found that mutational landscape varies significantly between the three groups of patients. The most mutated genes in MIA were EGFR and TP53. 4 out of 5 MIA cases harbored multiple alternations in EGFR catalytic domain and inactivating mutations in TP53 were found in 3 out of 5 patients. Furthermore, mutations in Wnt pathway genes were found in 4 out of 5 cases. Notably, mutations/amplification in Notch family was detected in 3 out of 5 cases (predominantly in the tumor invasive zone). In contrast to MIA, in AIS, only one case out of 5 harbors mutated TP53 or EGFR. Unlike in MIA, only one AIS patient carried mutated APC gene, suggesting that Wnt signaling plays insignificant role in AIS carcinogenesis. On the contrary, we found that AIS carcinogenesis heavily relies on alternations of AKT pathway, since aberrations in KIT, KRAS, HRAS, IGF1R, FGFR3, MET or TSC2 genes were found in 4 out of 5 patients. For AAH cohort we sequenced 25 independent lesions from 6 patients. Sequencing revealed that RAS and AKT/ERK pathways were most frequently affected in these lesions. In 3 cases we were able to track a possible cancer driving mutation from AAH to the primary tumor. This observation provides for the first time a direct link between AAH lesion and primary adenocarcinoma. Most of the patients in all groups carried mutations in genes associated with DNA repair and chromatin remodeling, suggesting that deregulation of the DNA repair machinery is an early onset event of adenocarcinoma tumorigenesis. In all groups our analysis revealed mutations in genes that have been never implicated in lung adenocarcinoma. Our study helps to understand the potential role of heterogeneous clonal events in the progression of early glandular neoplasms including the transition from non-invasive to invasive disease.
Citation Format: Eugene G. Izumchenko, Xiaofei Chang, Mariana Brait, William Westra, David Sidransky. Targeted sequencing for the assessment of intratumor heterogeneity. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1505. doi:10.1158/1538-7445.AM2014-1505