INTRODUCTION: Genetic abnormalities specific to post-Helicobacter pylori eradication gastric cancer (GC), especially those associated with undifferentiated post-eradication GC, are unknown. We conducted next-generation sequencing of GC diagnosed either before or after eradication to investigate the carcinogenesis of post-eradication GC. METHODS: Five cases of post-eradication differentiated GC [HP(-)-D group], five cases of H. pylori-positive differentiated GC [HP(+)-D group], four cases of post-eradication undifferentiated GC [HP(-)-U group], and six cases of H. pylori-positive undifferentiated GC [HP(+)-U group] underwent analysis. DNA was extracted from tumor samples, and non-tumor samples of all subjects. Next-generation target sequencing was conducted using the Ion AmpliSeq Library Kit 2.0 with the Ion AmpliSeq Cancer Hotspot Panel v2. Next-generation targeted sequencing results of the cancer part were subtracted from the results of the non-cancer part. RESULTS: The HP(-)-D group displayed significantly fewer SNPs in hotspot than the other groups (p <
0.01). Definitive DNA mutations were identified by sequencing of cancerous and non-cancerous tissues. 5 of 20 patients had specific somatic mutations, with different TP53 mutations in the HP(+)-D and HP(-)-U groups, CTNNB1 mutations in the HP(+)-U group, and ATM mutations in the HP(+)-U group, but no mutations in the HP(-)-D group. CONCLUSION: Several definite genetic mutations involved in GC were observed. Mutations were less frequent in post-eradication differentiated GC. However, because of small number of cases analyzed to identify carcinogenic differences, further analysis with a large number of cases and with strictly grading GC samples is needed.