Differentiated adenocarcinoma with a gastric phenotype in the stomach: difficulties in clinical and pathological diagnoses.

Differentiated-type adenocarcinoma with gastric phenotype of the stomach is rare and is difficult to diagnose both clinically and pathologically. We report a case of differentiated-type adenocarcinoma with a gastric phenotype in the stomach. A 60-year-old Japanese female was referred to our hospital with gastric cancer. A barium meal examination and esophagogastroduodenoscopy revealed a granular elevated lesion in the lower body near the lesser curvature and a depressed lesion on the antrum. A biopsy specimen showed benign atrophic mucosa in a granulated lesion and moderately differentiated adenocarcinoma in the depressed lesion. The patient underwent laparoscopy-assisted distal gastrectomy with lymph node dissection. The postoperative course was uneventful. Histological examination of the resected tissue confirmed well-differentiated adenocarcinoma in the granulated lesion and moderately differentiated adenocarcinoma in the depressed lesion, without lymph node metastasis. Both lesions were confined to the mucosa. Since mucin immunohistochemistry revealed MUC5AC-positive staining in the granulated lesion, the final diagnosis was differentiated-type adenocarcinoma with gastric phenotype in the stomach. Despite the high malignant potential, the clinical and pathological diagnoses of gastric-type differentiated adenocarcinoma are often difficult. Mucin immunohistochemistry together with hematoxylin and eosin (HE) staining may be helpful in the pathological diagnosis of this rare disease.