A case of undifferentiated carcinoma with osteoclast-like giant cells of the pancreas derived from an intraductal papillary mucinous neoplasm.

Pancreatic undifferentiated carcinoma with osteoclast-like giant cells (UC-OGC) is an extremely rare and aggressive malignancy. We report the case of a 71-year-old male who presented with a solid-and-cystic mass in the pancreatic head. The cut section of the pancreaticoduodenectomy specimen showed hemorrhagic polypoid lesions localized to the cyst spaces. Histological examination revealed a cystic background as an intraductal papillary mucinous neoplasm (IPMN) with low-grade dysplasia, while the intra-cystic polypoid mass was morphologically identical to giant cell tumors (GCT) of bone and soft tissue, consisting of a mixture of mononuclear histiocyte-like cells and multinucleated osteoclast-like giant cells. Nuclei of the mononuclear cells were similar to those of the multinucleated giant cells, showing no obvious atypia. The mononuclear cells were diffusely immunoreactive for CD163 and completely negative for all examined epithelial markers. Genetic analysis showed both the IPMN and the GCT-like components harbored identical double mutations of KRAS (G12V) and GNAS (R201C), and confirmed a diagnosis of UC-OGC originating from IPMN. This case emphasized that pancreatic UC-OGC can provide bland morphology, which is morphologically and immunohistochemically undistinguishable from GCT of the bone and soft tissue. Our study also highlights the importance of genetic analyses in properly diagnosing and managing such patients.