A case of osteoclast-type giant cell tumor of the pancreas with high-frequency microsatellite instability.

It has been reported that osteoclast-type giant cell tumor of the pancreas (OGTP) is rare, with a frequency of only 0.2% of the total reported pancreatic carcinomas. We report herein a rare case of OGTP in a 57-year-old Japanese man. Preoperative examinations showed a solid and cystic tumor, measuring 20 x 15 cm at the pancreas body. The resected specimen was a solid tumor with a giant cyst containing bloody contents. The tumor was composed of a proliferation of mononuclear cells admixed with osteoclast-type giant cells. The tumor cells were immunoreactive for vimentin, alpha1-antitrypsin, and EMA but not for CEA and cytokeratin. These findings indicated that this case was a malignant OGTP. The tumor cells showed microsatellite instability with high frequency (MSI-H). The present patient is alive 3 years after the operation, while OGTP has been reported to have a poor outcome. It has been reported that pancreatic carcinomas with MSI-H status have a favorable outcome. MSI-H might be one of the predictive markers for the long survival in OGTP.