Epstein-Barr virus (EBV)-associated gastric adenocarcinoma is a histological subtype of gastric adenocarcinoma, in which all of the carcinoma cells are basically positive for EBV-encoded small RNA (EBER) by in situ hybridization. Although its typical histology has some overlap with gastric carcinoma with lymphoid stroma, absence of massive lymphoid infiltrate is sometimes observed either in whole or in part. EBV-associated adenocarcinoma is one of the four representative molecular pathological subtypes recently identified by comprehensive genomic analysis of gastric adenocarcinomas. According to the analysis, typical EBV-associated gastric adenocarcinoma constitutes an independent molecular pathological subgroup, which is mutually exclusive to TP53-mutated adenocarcinoma with chromosomal instability, another molecular pathological subtype in gastric adenocarcinomas. Here, we report a rare case of gastric cancer heterogeneously composed of EBER (+)/TP53 (+) and EBER (-)/TP53 (-) portions. The EBER (+)/TP53 (+) component with massive lymphoid infiltrate surrounded the EBER (-)/TP53 (-) component showing well to moderately differentiated tubular adenocarcinoma. Although collision of two independent gastric cancers could be the simplest and most possible explanation for this situation, we discussed another possibility. In the case of gastric collision tumors, concurrent development of EBER (+) gastric adenocarcinomas and EBER (-) gastric adenocarcinomas in a single stomach is a rare incident. Since presence of the EBER (+)/TP53 (+) tumor component is atypical in itself, we also discussed the mechanism of development of the clone.
Keywords: Epstein-Barr virus; Gastric adenocarcinoma; TP53; adenocarcinoma with lymphoid stroma; collision tumor.