A Case Report of an Undifferentiated Pancreatic Carcinoma Diagnosed as a Solid Pseudopapillary Neoplasm before Surgery

: A 37-year-old man visited a previous hospital because of left abdominal pain. A contrast-enhanced CT scan revealed a 7 cm solid tumor in the pancreas body, and the patient was referred to our hospital. EUS-FNA showed that the tumor cells were positive for b-catenin in the nuclei, as well as for CD10 and CD56. On the other hand, the cells were negative for chromogranin A and synaptophysin. This is the typical immunohistochemical pattern of a solid pseudopapillary neoplasm(SPN). Therefore, we diagnosed this case as SPN before surgery. As the tumor progressed rapidly in 2 months, we performed distal pancreatectomy, total gastrectomy, and partial liver resection of the left lateral segment because of suspicious invasion of the pancreatic tumor to the stomach and the liver. On histological examination of the resected specimen, tumor invasion to the stomach was apparent, but the tumor did not invade the liver. Immunohistochemical staining showed the same SPN pattern as the EUS-FNA results. We identified small and uniform tumor cells, although no pseudopapillary pattern was observed with HE staining. Finally, we diagnosed this case as an undifferentiated carcinoma. We need to consider the possibility of malignant transformation or undifferentiated carcinoma even when a tumor is diagnosed as SPN on EUS-FNA.