Poorly differentiated adenocarcinoma misdiagnosed as gastrointestinal stromal tumor: A case report

Table 1 Comparison of pathological findings between endoscopic submucosal dissection biopsy and surgical specimen

Item	ESD biopsy specimen (initial assessment)	Surgical resection specimen (final diagnosis)
Specimen type	Limited endoscopic biopsy (partial submucosal tissue)	Full-thickness gastrectomy specimen
Tumor architecture	Fragmented tissue with spindle cell-like components	Infiltrative growth involving mucosa, submucosa, and muscularis propria
Cellular morphology	Elongated cells with hyperchromatic nuclei; limited structural context	Poorly differentiated adenocarcinoma with marked atypia
Mucosal involvement	Not adequately assessed	Definite ulceration with mucosal invasion
Depth of evaluation	Superficial and limited	Complete assessment of tumor depth
Immunohistochemistry	Not performed at initial stage	Tumor cells positive for epithelial markers (anti-epithelial antigen 1/anti-epithelial antigen 3, CK antibody monoclonal 5.2, CK7, CK8/18, epithelial membrane antigen, partial CEA); CD34 staining limited to vascular endothelial cells; CD117 and discovered on GIST-1 not performed
Diagnostic interpretation	Suggestive of gastrointestinal stromal tumor	Confirmed poorly differentiated adenocarcinoma

ESD: Endoscopic submucosal dissection; CK: Cytokeratin; CEA: Carcinoembryonic antigen; GIST: Gastrointestinal stromal tumor.