A Case of Pancreatic Undifferentiated Carcinoma Mimicking Proximal-Type Epithelioid Sarcoma

We herein report a case of pancreatic undifferentiated/anaplastic carcinoma pathologically mimicking proximal-type epithelioid sarcoma. The patient was a 35-year-old female who complained of epigastralgia and back pain and presented with tarry stools and weight loss. A growing, hemorrhagic pancreatic mass more than 6 cm in diameter and multiple liver masses were revealed on abdomen images. A liver biopsy showed malignant cells and chemotherapy using TS-1 was performed, however, the patient accumulated a large amount of ascites by diffuse peritoneal dissemination and died after seven months. An autopsy demonstrated the manifestation of a large whitish, expansive-infiltrative mass with severe hemorrhage, measuring 18 x 13 cm, seated primarily in the head of the pancreas. Microscopically, the tumor showed a medullary growth consisted of pleomorphic spindle to epithelioid cells, which were loosely cohesive and included rhabdoid morphology. The glandular component, suggestive of ductal adenocarcinoma, could not be found even with extensive sampling. Immunohistochemical studies showed a diffuse positivity of cytokeratin (AE1/AE3), epithelial membrane antigen, vimentin, and CD34 and a negativity of specific differentiation markers. In addition, a loss of SMARCB1/INI-1 protein expression was observed, although its alterations were not confirmed at the deoxyribonucleic acid level. No KRAS mutations were detected. The tumor was considered as pancreatic undifferentiated/anaplastic carcinoma from the similarity to "monomorphic anaplastic subtype of pancreatic undifferentiated rhabdoid carcinoma" recently proposed by Agaimy A et al. However, its histological, immunohistological and molecular characters were completely identical to those of PES, thus the clinical treatment and care for proximal-type epithelioid sarcoma may be recommended rather than those for undifferentiated/anaplastic carcinoma as a subtype of ductal adenocarcnoma.