Abstract 1437: Differential role of mutations in clonal evolution in esophageal mucosa at risk for cancer
Authors: Yokoyama Akira , Suzuki Hiromichi , Yoshizato Tetsuichi , Shiozawa Yuusuke , Sato Yusuke , Aoki Kosuke , Kakiuchi Nobuyuki , Takeuchi Yasuhide , Fujii Yoichi , Makishima Hideki , Yoshida Kenichi , Kataoka Keisuke , Shiraishi Yaichi , Sanada Masashi , Tsunoda Shigeru , Minamiguchi Sachiko , Miyano Satoru , Muto Manabu , Ogawa Seishi 
Published: July 2017

Abstract
Background Esophageal squamous cell carcinoma (ESCC) develops in close association with a chronic exposure to heavy drinking and smoking, frequently in a metachronous manner, suggesting a strong field effect on ESCC carcinogenesis. However, it is poorly understood how the field effect promotes clonal evolution in esophageal mucosa to induce dysplasia, eventually leading to the development of ESCC.
Patients & Methods A total of 221 samples were obtained by multiple sampling from cancer tissues (n = 53) as well as dysplastic (n = 12) and non-dysplastic (n = 156) mucosae from 49 cancer-bearing patients and 2 high-risk and 10 healthy patients either by endoscopy or surgery with different sampling sizes (regular size: 4 - 8 mm2 and small size: 0.2 or 0.8 mm2). All the samples were subjected to whole exome (WES) (n = 99) and/or targeted-capture (TS) (n = 221) sequencing. Copy number alterations (CNAs) were also investigated using SNP array- or sequencing-based karyotyping.
Results WES and TS in regular size samples revealed clonal proliferation in most of the non-dysplastic samples (98%), although the number of accompanying mutations and their clone size were significantly lower compared to those in samples from cancer and dysplasia (respectively, P = 0.021 and P &lt; 0.001). Non-dysplastic samples were most frequently accompanied by NOTCH1 mutations (75%), followed by TP53 mutations (50%). By contrast, cancer and dysplasia samples showed much lower frequencies of NOTCH1 mutations (19% and 66%), but instead characterized by higher frequency of TP53 mutations (100% and 92%), and CNAs (83% and 17%), especially those focally involving CCND1, CDKN2A, PIK3CA, and EGFR, respectively. Mutation signatures also differed significantly between samples from non-dysplastic mucosa, and cancer/dysplasia tissues; cancer/dysplasia samples exhibited an enhanced APOBEC-related and decreased transcription-coupled repair-related signatures, compared to non-dysplastic samples. In non-dysplasia samples, both NOTCH1 and TP53 mutations were significantly enriched in heavy drinkers compared to non- or occasional drinkers (p &lt; 0.001 and p = 0.023, respectively). To decipher the clonal architecture in more detail, we also sequenced 58 samples collected from non-dysplastic mucosae with a smaller sampling size. Clonal proliferation was confirmed in all the samples analyzed; NOTCH1 and TP53 mutations were found in 79% and 55% of the samples, where 78% and 27% of the mutated area showed biallelic alteration, respectively.
Conclusions Clonal proliferation in non-cancer esophageal epithelia is quite common even in non- or occasional drinkers and could be extensive in heavy drinkers. NOTCH1 and TP53 mutations as well as CNAs play major roles in clonal evolution but may have differential impacts on esophageal carcinogenesis, where TP53 mutation and CNAs are likely to make major contributions possibly under the influence of a higher APOBEC activity.
Citation Format: Akira Yokoyama, Hiromichi Suzuki, Tetsuichi Yoshizato, Yuusuke Shiozawa, Yusuke Sato, Kosuke Aoki, Nobuyuki Kakiuchi, Yasuhide Takeuchi, Yoichi Fujii, Hideki Makishima, Kenichi Yoshida, Keisuke Kataoka, Yaichi Shiraishi, Masashi Sanada, Shigeru Tsunoda, Sachiko Minamiguchi, Satoru Miyano, Manabu Muto, Seishi Ogawa. Differential role of mutations in clonal evolution in esophageal mucosa at risk for 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 1437. doi:10.1158/1538-7445.AM2017-1437