Experimental approach to fibrous histiocytoma.

A transplantable tumor was produced in syngeneic mice inoculated with transformed bone marrow macrophages (28-12- and L-18 cell lines). The tumor composed of proliferative spindle cells was arranged in a storiform pattern, and was similar to that of human fibrous histiocytoma. Electron microscopically, the tumorous spindle cells had fibroblastic characteristics, while functionally, the tumor cells had histiocytic characteristics, and consisted of a transitional form between histiocytes and fibroblasts. We consider the spindle cells to be facultative fibroblasts. This finding is compatible with the hypothesis that fibrous histiocytoma is derived from histiocytes.