Fibronectin in relation to growth patterns of fibrohistiocytic tumours--an immunohistochemical study of benign and malignant fibrous histiocytomas.

Benign and malignant fibrous histiocytomas are composed of an admixture of fibroblast-like and histiocyte-like cells and of a changing amount of fibre structures which tend to be arranged in a so-called storiform pattern. In order to study the organization of the extracellular matrix, the distribution of fibronectin was investigated immunohistochemically. Using the PAP technique and the indirect immunofluorescence method, paraffin sections of formaldehyde fixed tissue specimens of 25 tumours (12 benign fibrous histiocytomas, 12 malignant fibrous histiocytomas, and 1 atypical fibroxanthoma) were studied. A pretreatment with hyaluronidase and proteolytic enzymes (trypsin, pronase, pepsin) was performed to unmask the antigen. Best results were obtained with pronase E or, sometimes even better, by employing a combination of pronase E and hyaluronidase. Generally fibronectin could be demonstrated in the matrix substances of fibrohistiocytic tumours, but the immunohistochemical staining patterns of benign and malignant tumours differed. In benign fibrous histiocytomas, a regular distribution of fibronectin was found in cellular areas. Parallel to formation of collagen fibres, the reaction decreased and in dermatofibromas showing abundant hyalinized collagen the staining proved to be quite weak. In malignant fibrous histiocytomas, the immunostaining was very irregular. In cellular areas consisting of spindle cells, an intense reaction could be observed. Tumours with storiform or fascicular fields exhibit a delicate network of fibronectin encircling individual fibroblast-like cells. In the course of fibre formation, the matrix staining for fibronectin revealed a distribution similar but not identical with that obtained with the reticulin stain. Simultaneous to the occurrence of collagen fibre bundles, fibronectin decreased and in areas of hyalinization the staining was considerably diminished. In areas of undifferentiated small cells, in myxoid zones as well as foci of xanthoma cells, and in pleomorphic portions the immunostain was negative. The distribution in atypical fibroxanthoma is similar to that observed in storiform and pleomorphic variants of malignant fibrous histiocytomas. The results support the suggestion that fibronectin is the first sign of the typical basic pattern of fibrohistiocytic tumours preceding the formation of reticulin and collagen fibres. The expression of fibronectin on cell surfaces as well as in intercellular matrix may be closely related to the organization of the growth patterns of fibrohistiocytic tumours.