Abstract: Neoplasms characterized by the expression of markers of neuroendocrine differentiation in neoplastic cells are defined as neuroendocrine neoplasms. A case of neuroendocrine carcinomas (NECs) with a small amount of papillary adenocarcinoma and significantly vacuolar nucleus at the esophagogastric junction was reported in this article. A 77-year-old male had dysphagia for one week. Endoscopy revealed early-stage esophagogastric junction carcinoma, and biopsy was diagnosed as poorly differentiated carcinoma. Endoscopic submucosal dissection was performed. Histologically, the papillary adenocarcinoma progresses from typically branching papillary structures (well-differentiated) to hyperplasia of the lining epithelium of the papilla to form a cribriform structure (moderately differentiated), to solid area lacking papillary structures (poorly differentiated). There was a continuous process, and during this process, the vacuoles in the nuclei of tumor cells showed progressive changes from mild to obvious and finally to significant vacuoles. The tumor was mainly composed of solid areas (about 95%), with single cell, large cell, round or oval to irregular nuclei, and significantly vacuolar nuclei, nuclei with larger vacuoles appeared in a loop, a few thin weakly basophilic or weakly eosinophilic fine particles could be seen in the vacuoles, and the vacuoles had rough edges. The nucleus chromatin at the outer edge of the vacuoles was fine particles, and mitosis was common (20-30/mm²), atypical mitosis could be seen, and nucleoli could be seen easily, the cytoplasm was weakly eosinophilic, and the boundaries of cells were unclear. The cells were arranged in a nested, trabecular, or diffuse sheet shape, with some arranged in a glandular tube shape. Tumor thrombus was found in the vein of submucosa; the interstitial tissue rich in capillaries within the tumor was accompanied by a large number of neutrophil infiltration. Immunohistochemical staining showed that the solid area of the tumor was positive for synaptophysin (Syn) and chromogranin A (CgA), while papillary adenocarcinoma was negative. Mucin 5AC (MUC5AC) was diffusely positive in papillary adenocarcinoma, while the proportion of positive cells in the solid area of the tumor was about 10% to 15%. In a word, this case showed the extreme situation of the vacuolar nuclear characteristics of NECs, extremely rare, in a sense, this case expanded the boundary of the morphological spectrum of NECs. Understanding the extreme vacuolar features of this nucleus is helpful to make a correct pathological diagnosis.

Key words: Esophagogastric junction, Papillary adenocarcinoma, Neuroendocrine carcinomas, Vacuolar nucleus