Giant cell tumor of the pancreas arising in the ovarian-like stroma of a mucinous cystadenocarcinoma

We describe a malignant mucinous cystic neoplasm of the pancreas with ovarian-like stroma within which an osteoclast-like giant cell rich tumor arose. This rare tumor had a unique immunohistochemical profile with the giant cells staining for vimentin, leukocyte common antigen, and the monocyte/macrophage marker CD68, whereas the mucinous epithelium stained for epithelial membrane antigen and cytokeratin. The immunohistochemical findings are consistent with two lines of differentiation, one epithelial and the other suggesting mesenchymal differentiation of the giant cell tumor with an immunophenotype similar to giant cell tumor of bone. The coexistence of these two rare tumors suggests that they are histogenetically related. The finding of a giant cell tumor arising in the ovarian stroma indicates that the stroma of mucinous tumors is not always an innocuous component of the tumor.