Gastric carcinoma with lymphoid stroma partially differentiated into squamous cell carcinoma

Abstract

A 49-year-old man was referred to our hospital because of an elevated gastric lesion. EGD revealed a submucosal tumor-like elevated lesion 15 mm in diameter, with surface depressions on the greater curvature of the gastric antrum with atrophic gastritis (A, B). EUS revealed a hypoechoic multinodular mass in the submucosal layer (C). Endoscopic forceps biopsy revealed squamous cell carcinoma (SCC). Computed tomography scan and positron emission tomography-computed tomography showed no obvious malignancy. We resected the lesion en bloc, as a total excision biopsy, by endoscopic submucosal dissection. Histologic analysis revealed a gastric carcinoma with lymphoid stroma invading the deep submucosal layer (pT1b 2000 μm) without lymphovascular permeation and with negative margins, which consisted of poorly differentiated adenocarcinoma and SCC. Whole tumor cells including the SCC component were diffusely positive for Epstein-Barr encoded ribonucleic acids (RNAs) by in situ hybridization. Immunohistochemical staining showed that the SCC component was positive for p40 and cytokeratin 5/6 (D, CK5/6 immunostaining, orig, mag. ×20). No precursor nonneoplastic squamous metaplasia was observed in the resected specimen. These findings suggested that this was an extremely rare case of gastric carcinoma with lymphoid stroma partially differentiated into SCC.