Osteoclast-like giant cell tumour of the pancreas presenting as a pseudocyst-like lesion.

A 57-year-old male patient presented with a cystic lesion in the tail of the pancreas, which was considered to be a pseudocyst. He was treated by cystojejunostomy but one year later a tumour was found to have invaded the stomach and jejunum. This was an osteoclast-like giant cell tumour containing a small area of typical ductal adenocarcinoma. Immunohistochemical staining revealed that the pleomorphic tumour cells were positive for cytokeratin, epithelial membrane antigen, vimentin and the proliferation marker MIB-1. The osteoclast-like giant cells and some small histiocytic cells stained for leukocyte common antigen and histiocytic markers and were negative for MIB-1. At autopsy, tumour rests were found in the pancreas but there were no metastases. Osteoclast-like giant cell tumours of the pancreas may present as cystic lesions and should be included in the differential diagnosis of pseudocysts.