Tumor cells of malignant fibrous histiocytomas express mRNA for laminin.

In situ hybridization was used on routinely processed paraffin-embedded tissue sections to study the synthesis of the basement membrane (BM) proteins laminin and type IV collagen in 14 cases of malignant fibrous histiocytoma (MFH). Complementary RNA probes coding for the pro-alpha 1 (IV) chain of human type IV collagen and the B1 chain of human laminin were used to detect the respective mRNAs. The results were correlated with the immunohistochemical reactivity of tumor cells to specific antibodies against the P1 fragment of laminin and the 7S domain of type IV collagen. Signals for the presence of laminin mRNA in atypical neoplastic tumor cells could be detected in 11 MFHs. None of the tumors could be shown to contain signals for type IV collagen mRNA in their cells, although such signals were detected in the endothelial cells of tumor capillaries. In the corresponding immunohistochemical stainings, nine MFHs showed intracytoplasmic staining of tumor cells for laminin and one tumor showed weak staining for type IV collagen in the neoplastic cells. The results show that the laminin immunoreactivity found in MFHs is due to synthesis in the tumor cells and not to endogenous uptake of this protein. Synthesis of laminin in the majority of MFHs is in accordance with the notion that these tumors originate from primitive mesenchymal cells in soft tissues.