RHOA mutations and CLDN18-ARHGAP fusions in intestinal-type adenocarcinoma with anastomosing glands of the stomach.

A subtype of intestinal-type adenocarcinoma of the stomach, characterized by low-grade cytological atypia and anastomosing glands, has been described in several reports under different names. One of the remarkable features of these lesions, herein referred to as intestinal-type adenocarcinoma with anastomosing glands, is the frequent association of poorly differentiated adenocarcinoma components. Here we analyzed 44 intestinal-type adenocarcinomas with anastomosing glands focusing on the molecular abnormalities that are common in diffuse-type gastric cancers. Next-generation sequencing identified RHOA and CDH1 mutations in 22 (50%) and one lesion (2%), respectively. Reverse transcription-PCR detected CLDN18-ARHGAP fusions in three lesions (7%). Immunohistochemically, none of the lesions showed abnormal p53 expression patterns whereas focal and diffuse loss of ARID1A was observed in four and one lesion, respectively. Examination of 37 lesions of dysplasia and 26 usual-type intramucosal adenocarcinomas identified one RHOA mutation in adenocarcinoma and no CLDN18-ARHGAP fusions, indicating that these genetic alterations are highly specific to intestinal-type adenocarcinomas with anastomosing glands among differentiated-type intramucosal neoplasms. The present study showed that intestinal-type adenocarcinoma with anastomosing glands represents a genetically distinct group of tumors with the frequent presence of RHOA mutations and CLDN18-ARHGAP fusions, which are thought to be specific to diffuse-type gastric cancers.