Abstract 1434: Mutational landscape in the normal-appearing airway cancerization field of early-stage non-small cell lung cancer

Abstract

Abstract Lung cancer, of which non-small cell lung cancer (NSCLC) is the most common form, is the second most prevalent cancer in the U.S. and the leading cause of cancer mortality. Field cancerization phenomenon establishes that normal appearing tissues surrounding a tumor will exhibit a field effect – particularly in smokers – with the tissues proximal to the tumor showing more, and even sharing, alterations with the tumor. Previous studies in NSCLC provide evidence for both complex progression trajectories, yet, precise mechanisms remain unknown. To investigate the field cancerization phenomenon, we conducted a genome-wide survey of acquired DNA alterations in normal-appearing tissues including small airways adjacent to NSCLC, mainstem bronchi (large airways), nasal epithelium, distant normal lung and blood, along with multiple samples from their surgically resected paired tumors, for a total of 500 samples from 48 patients with early-stage NSCLC (11 squamous cell carcinomas and 37 adenocarcinomas). Since we expect low mutation burdens and mutant cell fractions in pathologically normal tissues, we assessed somatic point mutations via deep targeted sequencing of 409 genes and paired these data with our recent study of acquired copy number alterations (CNAs) inferred from high-density whole-genome SNP microarrays, thus offering a deep and wide survey of somatic DNA alterations. After aggregating results from multiple mutation callers, we observed somatic mutations (exonic, splicing and UTRs) in 257 samples of which 65 (in 35 patients) were from normal-appearing field (non-tumor, non-blood) samples. Tumor and field samples in smokers showed a higher mutation burden and large proportion of C:G>A:T changes. We also observed concordance of mutations in the airway and corresponding tumor profiles. Further, a statistically significant field effect was established with mutational burden (measured by the variant allele frequency) increasing with proximity to the tumor. Among the 35 NSCLC cases with field mutations, the small adjacent (to tumor) airways in six patients exhibited mutations in lung cancer drivers such as KRAS, STK11, TP53 and KEAP1. We also identified mutations in the large airway (TP53, SETD2, CDKN2A), distant normal lung parenchyma (RB1, RET) and nasal epithelium (AKT1). We then correlated point mutation and CNA mutation profiles. Of eight cases showing a nonsynonymous or stopgain variants in established lung cancer drivers in the airways, four exhibited putative “two-hit” progression models, e.g. both KEAP1 and STK11 mutations with 19p loss, overlapping TP53 mutation/17p loss, or KRAS mutation/12p gain. Our findings in normal-appearing tissues of the respiratory epithelium offer insights into the earliest mutational events in their progression to NSCLC and, possibly, in tumor relapse and that may represent suitable targets for early detection and chemoprevention. Citation Format: Smruthy Sivakumar, Yasminka Jakubek, Wenhua Lang, Tina McDowell, Melinda M. Garcia, Chi-Wan Chow, Zachary Weber, Carmen Behrens, Neda Kalhor, Cesar Moran, Randa El-Zein, Gareth Davies, Junya Fujimoto, Reza Mehran, Stephen G. Swisher, Jing Wang, Avrum E. Spira, Jerry Fowler, F Anthony San Lucas, Ignacio I. Wistuba, Erik Ehli, Paul Scheet, Humam Kadara. Mutational landscape in the normal-appearing airway cancerization field of early-stage non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1434. doi:10.1158/1538-7445.AM2017-1434