Vimentin, actin, desmin, CD34, and CD68

Vimentin is a 57-kDa protein, a member of the type III family of intermediate filaments, expressed in all mesenchymal cells forming an important part of the cytoskeleton of these cells. The type III family of intermediate filaments includes vimentin, desmin, GFAP, and peripherin. Vimentin is generally expressed in all primitive cells in the early embryogenesis and be replaced by other intermediate filaments during maturation and differentiation.

The use of vimentin as a single marker is of limited diagnostic value as the co-expression of vimentin with other different cytokeratins has been demonstrated in many types of epithelial cells and tumors such as carcinomas of the lung, salivary glands, liver and biliary tract, thyroid gland, adrenal cortex, kidney, endometrium, gonads and meningioma (Fig. 22.1). Generally, poorly differentiated carcinomas may acquire vimentin expression with loss of keratins and finally resulting a sarcomatoid phenotype. For diagnostic purposes, vimentin can be only used as a part of diagnostic antibody panel.

STAT-6 is a member of the STAT family of cytoplasmic transcription factors involved in the modulation of signal transmission between DNA promoters and cell receptors. The inv. (12)(q13;q13) is a chromosomal aberration characteristic for solitary fibrous tumor generating the NAB2-STAT6 fusion transcript causing the overexpression of the STAT-6 protein, which is a characteristic immunohistochemical marker for solitary fibrous tumor (Fig. 22.2). This chromosomal abnormality affects also the promoter of the ERG-1 gene causing the overexpression of the ERG-1 transcription factor, which can be a further marker for this tumor identity [1, 2].

The overexpression of STAT-6 is also found in a limited number of other mesenchymal tumors including meningeal hemangiopericytoma that carries the same genetic abnormality, subset of dedifferentiated liposarcoma, and desmoid tumor [3–5].

MUC-4 is a transmembrane mucoprotein mentioned in a previous chapter with other mucins. In addition to glandular epithelial tumors, the expression of MUC-4 is also a characteristic marker for low-grade fibromyxoid sarcoma, sclerosing epithelioid fibrosarcoma, and glandular components in biphasic synovial sarcoma [6, 7].