SPP1 and mesenchymal cell neoplasm: However, Bramwell et al. have shown that benign mesenchymal tumors, such as lipomas, borderline-malignant dermatofibrosarcomas and well-differentiated/myxoid liposarcomas do not express OPN, while other subtypes of malignant STS of histological grades 2 or 3, display strong expression of OPN in over 80% of samples (Bramwell et al. 2005).