Abstract 164: Clonal evolution in noncancerous esophageal mucosa in normal and cancer-bearing individuals

Abstract

Abstract Background Esophageal squamous cell carcinoma (ESCC) represents the most common form of esophageal cancer worldwide, especially in East Asia, where alcohol drinking and smoking have been implicated in the field carcinogenesis of ESCC. However, the oncogenic process therein has been poorly understood in terms of gene mutations. Patients & Methods A total of 100 samples, including cancer, dysplastic, and non-dysplastic esophageal tissues, were obtained from 24 individual with (N = 14) or without (N = 10) ESCC (a median of 2.5 samples per case: 1−29) either by endoscopy or surgery and were subjected to whole exome sequencing (WES). An additional paired cancer/non-caner samples from 32 patients was analyzed by targeted sequencing (TS). All samples were analyzed for copy number alterations (CNAs) using SNP array- and/or digital sequencing-based karyotyping. Results In WES, clonal evolution in esophageal epithelia, as determined by the presence of somatic mutations, was detected in 21 of 21 cancer, 12 of 12 dysplastic, and 63 of 67 non-dysplastic samples, where the mean number of mutation per sample showed a significant trend to increase in cancer (65) and dysplastic samples (50) compared to non-dysplastic samples (13) (P = 2.1×10-11). CNAs, especially those involving CDKN2A, CCND1, YAP1, and EGFR, were frequently affected in cancer samples, but rarely so in non-dysplastic samples. Non-dysplastic samples tended to have smaller allelic burden and therefore, clone size, compared to dysplastic and cancer samples (P = 2.2×10-16). Mutations had a predominant age-related signature in non-dysplastic samples but increasing APOBEC3A/3B patterns was observed in cancer and dysplastic samples. Shared mutations were found only within cancer tissues but never among dysplastic or non-dysplastic samples, suggesting the latter lesions are clonally independent from each other. In accordance with previous reports, TP53 mutations were found in 21/21 cancer samples and also found in dysplastic (11/12) and non-dysplastic samples at a lower frequency (26/67). Strikingly, non-dysplastic samples harbored a very high frequency of NOTCH1 mutations (51/67), which were also found in cancer (3/21) and non-dysplastic (8/12) samples but at much lower frequencies (P = 6.6×10-7). TS of validation samples confirmed the trend of higher NOTCH1 (84% vs. 25%) and lower TP53 mutation rates (38% vs. 100%) in non-dysplastic samples compared to cancer samples. The number of mutations in non-dysplastic samples was higher in drinkers than non-drinkers. Multiple NOTCH1 mutations were more common in cancer patients and drinkers than non-drinkers. Conclusion Clonal proliferation in non-cancer esophageal epithelia is common even in non-ESCC cases and extensive in ESCC cases. NOTCH1 and TP53 mutations play major roles in clonal evolution in common but may have differential impacts on esophageal carcinogenesis, which is likely to be shaped by APOBEC-induced mutations and CNAs. Citation Format: Akira Yokoyama, Hiromichi Suzuki, Tetsuichi Yoshizato, Kosuke Aoki, Yusuke Shiozawa, Youichi Fujii, Yusuke Sato, Nobuyuki Kakiuchi, Sugi Kin, Keisuke Kataoka, Kenichi Yoshida, Hideki Makishima, Yusuke Amanuma, Shinya Oohashi, Yuichi Shiraishi, Kenichi Chiba, Hiroko Tanaka, Brown J.B., Masashi Sanada, Shigeru Tsunoda, Sachiko Minamiguchi, Yoshiharu Sakai, Hironori Haga, Tsutome Chiba, Satoru Miyano, Manabu Muto, Seishi Ogawa. Clonal evolution in noncancerous esophageal mucosa in normal and cancer-bearing individuals. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 164.