Uterine müllerian adenosarcoma with histiocytic (xanthomatous) mesenchymal component

We present an endometrial Müllerian adenosarcoma in which the sarcomatous component showed prominent nests of foamy cells that accounted for 50% of the neoplastic mesenchyma. Such foamy cells showed occasional cytological atypias and immunohistochemical features of histiocytic (macrophagic differentiation in the absence of changes that could substantiate the presence of an inflammatory infiltration of foamy histiocytes. These facts suggest histiocytic differentiation from neoplastic mesenchymal cells. Such differentiation has been reported in association with malignant mixed mesodermal tumor, but not in Müllerian adenosarcoma.