Foreign-body tumorigenesis in rats by various kinds of plastics--induction of malignant fibrous histiocytomas.

Five kinds of plastics (3 polyvinyl chlorides, 1 polyhydroxyethyl metacrylate and 1 dimethyl polysiloxane) were implanted into subcutaneous tissues of Wistar rats of both sexes. Subcutaneous tumors developed in all experimental groups. The incidences of the tumors, however, differed from each other, although these materials were tested on the same experimental condition. This result indicates that chemical characters of the materials may influence the incidence of subcutaneous tumors. Histologically, most of these subcutaneous tumors were mesenchymal tumors with spindle cells arranged in a storiform pattern, with sheets of histiocyte-like cells or pleomorphic giant cells. Electron microscopy showed mixture of fibroblastic cells, histiocytic cells and undifferentiated cells in these tumors. From these histological and electron microscopical findings, many of the tumors were diagnosed as malignant fibrous histiocytomas.