Immunoreactivity for laminin and type IV collagen in malignant and benign fibrous histiocytoma

Sixteen malignant fibrous histiocytomas (MFH) and ten benign fibrous histiocytomas of the skin were studied immunohistochemically for the distribution of two basement membrane (BM) proteins, laminin and type IV collagen, in order to evaluate their cellular nature. Linear staining for both proteins was present in the vascular BMs. Intracytoplasmic laminin was observed in the neoplastic fibroblast-like and pleomorphic giant cells in 11 MFHs. Two MFHs also showed similar staining for type IV collagen. In the giant cell subtype of MFH, the reactive giant cells were totally negative whereas the neoplastic cells were strongly positive for laminin. Extracellular fibres staining positively for both BM proteins were seen in two MFHs. Except for the capillary network, the benign fibrous histiocytomas were negative for laminin and type IV collagen. On the basis of the present results, we favour the concept that MFHs are primitive mesenchymal tumours, some of which may show histogenetic relationships with tumours of BM forming mesenchymal cells.