Malignant giant cell tumour of the uterus.

Two rare cases of malignant giant cell tumours of the uterus in pure heterologous form are presented. Light microscopy showed numerous osteoclast-like cells in a background of spindle cells. Immunohistochemistry demonstrated Vimentin, Actin, alpha-1-antitrypsin and LCA in the latter, and Vimentin, alpha-1-antitrypsin and LCA in the giant cells while tartrate resistant acid phosphatase reactivity was demonstrated in both mononuclear cells and giant cells. Electron microscopy did not reveal smooth muscle or epithelial differentiation. The findings suggest a common origin of malignant giant cell tumours and malignant fibrous histiocytomas.