Comparison of various basement membrane components in benign and malignant peripheral nerve tumours.

Immunohistochemical methods were used to analyse benign and malignant tumours of peripheral nerve tissue. We tested for the distribution of basement membrane (BM) components collagen IV, laminin, heparan sulphate proteoglycan, fibronectin, for S100 protein and for the presence of interstitial collagens III and V. Laminin was generally noted in association with Schwann cells, but collagen IV occurred with perineural cells. When tested for BM components, fibroblasts were notably non-reactive except for fibronectin. Three specific area-dependent BM patterns were observed in the benign tumours: (a) Schwann cell-like, in fascicular areas (Antoni A areas of schwannoma, central fibrous bundles of plexiform neurofibromas and central areas of cutaneous neurofibroma), (b) perineural cell-like (capsular structures of schwannoma) and (c) fibroblast-like (myxoid and fibrously transformed areas). Most malignant tissues showed a variably fragmentary focal deposition of laminin. Other BM components were present only in well-differentiated areas. Poorly differentiated tumours demonstrated fibronectin reactivity alone. Our results provide evidence that the specific staining pattern for BM components helps to differentiate the various cellular proliferations in neurogenic tumours. Schwann cells are not only distinguishable from perineural cells by S100 protein staining, but also by their specific BM staining. In addition, perineural cells can be separated from fibroblasts, which do not express BM material. The "tropism" of laminin in normal nerves and benign neural tumours--which persists in neurogenic sarcomas--indicates preferential Schwann cell differentiation in these cells.