Identification of early genetic changes in well-differentiated intramucosal gastric carcinoma by target deep sequencing

Background and aims The recent advancement of next-generation sequencing (NGS) has enabled the identification of cancer-related somatic aberrations in advanced gastric cancer. However, these remain unclear in early gastric cancers, especially in intramucosal gastric cancers. Patients and methods Thirty-one well-differentiated (tub1) intramucosal gastric cancers obtained by endoscopic submucosal dissection (ESD) from 29 patients were analyzed. After precise collection of tumors and non-tumors from formalin-fixed paraffin-embedded tissues using laser-captured microdissection (LCM), target sequencing analysis of 50 cancer-related genes was performed using an Ion-Proton sequencer. Results The most frequent hotspot mutation was found in TP53 (17 lesions, 54.8%) followed by the Wnt -signaling pathway genes, APC and CTNNB1 (6 lesions, 19.4%). The mutations in TP53 and the Wnt -signaling genes were mutually exclusive ( p = 0.004). There was a tendency that H. pylori infection ( p = 0.082) and macroscopic protrusion ( p = 0.095) was associated with the presence of these mutations. Only 10 lesions (59%) among 17 lesions with proven TP53 mutations were positive for p53 immunostaining demonstrating the superiority of the mutational analysis. In addition, focal gene amplification of ERBB2 (16%) was found frequently in these early stage lesions. Conclusions Using LCM and NGS, mutations in TP53 and the Wnt- signaling pathway were frequently found and were mutually exclusive in the earliest stage of gastric carcinogenesis.