| Summary: | We report a case of gastric invasive micropapillary carcinoma (IMPC) in an 86-year-old female patient. She was admitted to our hospital with a chief complaint of bloody emesis. Upper gastrointestinal endoscopy found a gastric adenocarcinoma at the antrum. The biopsy specimens showed moderately differentiated adenocarcinoma with invasive small tumor nests. Distal gastrectomy with systematic lymph node dissection demonstrated that the tumor had IMPC through a pathological examination. Despite the depth of tumor invasion (the submucosa), extensive lymph node metastases were observed. Anti-D2-40 immunostaining revealed numerous infiltrating tumor cell nests in the lymphatic vessels, which could explain subsequent multiple lymph node metastases. The adenocarcinoma showed intestinal phenotypes by several immunohistochemical studies. One of these antibodies (CD10) clearly demonstrated the inverted apical-basal (inside-out) pattern of IMPC, whereas it showed an ordinary pattern in intestinal metaplasia adjacent to the tumor. Furthermore, genetic analysis by direct sequencing revealed a point mutation in the exon 5 of TP53 in the tumor. The mutation presumably harbors a missense mutation from Arg to His at the codon 175 (R175H). R175H has been previously described as a ‘gain-of-function' mutation with a high invasive or metastatic potential in several types of cancers. In summary, this is one of the first reported cases of gastric IMPC with intestinal phenotypes harboring a TP53 R175H mutation in the literature.
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