As defined by microscopic histopathologic analyses of hematoxylin and eosin stained tissue samples,<unk>  tumors vary from lower to higher cellular lesions. These cells are small-to-moderate-sized epitheliod-like cells that on ultrastructural analyses have features of fibroblasts and myofibroblasts. The cells contain moderate numbers of mitochondria, abundant rough endoplasmic reticulum networks, large Golgi complexes, and cytoplasmic arrays of vimentin intermediate filaments. The cells tend to be grouped into nests, sheets, cords, and/or single files embedded in an eosinophilic (i.e. more blue or purple compared to normal connective tissue because of excessive uptake of the hematoxylin stain), sclerotic (i.e. hardened) connective tissue background. The connective tissue background contains irregular, thin-walled, distended blood vessels and may have foci of hyaline cartilage, bone formation, and necrosis (clumps of dead or dying cells). Immunohistochemical analyses find that the neoplastic cells in<unk>  tumors typically express MUC1, vimentin, Bcl-2, CD99, and MUC4 marker proteins. MUC1, vimentin, CD99, and Bcl-2 marker proteins are expressed in the neoplastic cells of various types of other tumors and therefore do not distinguish between these tumors and<unk> . However the expression of MUC4 is found mainly in the neoplastic cells of<unk>  and low-grade fibroblastic tumors. Consequently, the expression of the MUC4 marker protein in tumor cells suggests that these tumors are either a<unk>  or low-grade fibromyxoid sarcoma rather than certain mimickers of<unk> .<unk>  tumors with MUC4-negative neoplastic cells may be more aggressive than<unk>  tumors with MUC4-positive neoplastic cells.
Sclerosing epithelioid fibrosarcoma
Angiomyofibroblastoma
Perivascular epithelioid cell tumour
Low-grade fibromyxoid sarcoma
Lymphoepithelioma-like carcinoma
Multinucleate cell angiohistiocytoma
Undifferentiated pleomorphic sarcoma
Plexiform angiomyxoid myofibroblastic tumor