Gut-associated lymphoid tissue carcinoma analyzed using next-generation sequencing: A case report.

Tumors related to the gut-associated lymphoid tissue (GALT) have been recently described. GALT carcinomas (GCs) have a characteristic appearance: macroscopically, they appear as a "dome-type" lesion, whereas microscopically, they show dilated cystic glands in the submucosa, differentiated adenocarcinoma without goblet cells, and stromal lymphocytes with germinal centers. However, their origin and pathogenesis remain controversial. Here, we present the case of a 54-year-old man that presented with a protruding lesion in the upper rectum during colonoscopy and had no family or past medical history. Low anterior resection was performed, and the tumor was diagnosed as GC based on its typical morphology. The tumor cells were negative for Mucin 2 and other mucins and CD10. p53 showed null-type. The tumor was associated with rich lymphocyte infiltration and germinal centers. Next-generation sequencing detected EGFR missense and TP53 nonsense mutations. Although GCs are known as conventional colorectal carcinomas that invade the submucosa, this case showed no neoplastic lesion in the mucosal epithelium in situ. Moreover, we detected EGFR and TP53 mutations (no pathogenic APC or KRAS mutations), which are not conventional adenoma-carcinoma mutations. Further studies are warranted to confirm whether GC is a sporadic carcinoma that invades the GALT submucosa.