This is abrief article about various substances that are expressed in the body and are used as tumour markers too.
Epithelial Markers
Keratins are the markers most frequently used in the identification of epithelial phenotypes.
Epithelial membrane antigen (EMA)
EMA represents a membrane glucoprotein that is most likely similar or identifical to the casein fraction of human milk. It is expressed by virtually all epithelial cells and neoplasm of epithelial origin. It is also expressed on a wide range of tumors of mesenchymal origin and even on some lymphomas.
Muscle Markers
Desmin, actin and myoglobin are the most frequently used markers of muscle differentiation.
Actin
Actin is a collective term describing a group of contractile filaments. Actins are divided into three major subgroups: alfa, beta, and gama. The three forms of alfa actin are organ or tissue specific and are designated as alfa-skeltal, alfa-cardiac, and alfa-smooth muscle.
The two forms of gama-actins are gama-smooth muscle and gama-cytoplasmic. There is only one form of beta-actin, and it is designated as beta-cytoplasmic. Beta and gama-cytoplasmic actins are ubiquitous and are expressed in virtually all cells. On the other hand, the expressions of alfa actins (skeletal, cardiac, and smooth muscle) as well as gama-smooth muscle actin are tissue specific.
As with desmin, actin is expressed on various cells that perform contractile functions such as myofibroblasts, myoepithelial cells, and pericytes. In bone tumors, antibodies against actin are frequently used in the differential diagnosis of primary and metastatic spindle and round-cell tumors.
Myoglobin
Myoglobin is the heme metalloprotein that binds oxygen and is expressed in skeletal muscle fibers. In contrast to other muscle markers, it is not expressed in smooth muscle cells.
It serves as a marker of skeletal muscle differentiation and is used in the diagnosis of rhabdomyosarcoma.
However, its expression is restricted to tumor cells with more differentiation, and most poorly differentiated tumors do not express sufficient amounts of this protein to be identified in paraffin-embedded, formalin-fixed tissue.
Vascular Markers
Factor VIII
Factor VIII-associated antigen, or von Willebrand factor can be demonstrated in all normal endothelial cells and is expressed by virtually all benign vascular lesions.
There is great variability of its expression in malignant vascular lesions.
High-grade angiosarcoma may show only focal positive staining. In skeletal pathology, it is most often used to disclose the endothelial nature of tumor cells in vascular lesions such as hemangioendothelioma.
Platelet-endothelial adhesion molecule (CD31)
CD31 is a member of the immunoglobulin family and represents a transmemebrane protein of endothelial cells. It is also expressed by megakaryocytes and platelets and can be detected in some plasma cells. It is expressed by virtually all benign vascular tumors and by a high percentage of malignant vascular lesions .
Human Progenitor cell antigen (CD34)
CD34 is a member of a large, superfamily of lymphoid markers. The expression of CD34 is not restricted to endothelial cells. Unfortunately, it is also present in a wide range of spindle cells and peripheral nerve sheath tumors. Therefore the applicability of CD34 in the differential diagnosis of vascular lesions is limited.
Neural Markers
S-100 protein
S-100 protein is an acidic nuclear protein that binds calcium and is composed of two (alfa and beta) subunits. S-100 protein is often used in the differential diagnosis of tumors of neural origin and melanoma.
In bone tumors, S-100 protein is more frequently used as a marker of cartilaginous differentiation. It can be identified in tumors exhibiting relatively primitive cartilaginous differentiation such as in chondromyxoid fibroma, chondroblastoma, and mesenchymal chondromyxoid fibroma, chondroblastoma, and mesenchymal chondrosarcoma.
S-100 protein is expressed by chordal tissue, and its expression is retained in chordomas. It is frequently used in the differential diagnosis of chordoma, chondrosarcoma, and the so-called chondroid chordoma.
Neuron-specific enolase
Neuron-specific enolase is an enzyme of the glycolytic pathway. Different isoenzymes of the group have tissue-specific expression to some extent.
Beta-beta dimeric form is expressed in skeletal muscles, the alfa-alfa form is present in glial cells, and the gama-gama isoform is present in neurons.
In bone tumors, it is most frequently used in the diagnosis of Ewing’s sarcoma and related conditions. It is also used in the diagnosis of neuroblastoma and other metastatic or primary bone tumors with potential neural differentiation.
Myelin basic protein
Myelin basic protein is a major polypeptide component of the myelin. Hence, it is expressed in tumors derived from the Schwann cells, both benign and malignant.
Leu-7
Leu-7 was identified as a marker of natural killer cells, but it is also present in the nerve sheath and neuroendocrine cells. It is typically used in the differential diagnosis of spindle-cell neoplasm with a presumed nerve sheath origin. Leu-7 is also expressed in tumors such as leiomyosarcoma, synovial sarcoma, and occasionally in rhabdomyosarcoma. It is also used in the differential diagnosis of small blue-cell neoplasms. Like neuron-specific enolase, it cannot be used as the sole marker of neural differentiation.
Synaptophysin
Synaptophysin is expressed in neural cells and is found in the presynaptic vesicles. It is also expressed in neuroendocrine cells. Synaptophysin is generally used as a sensitive marker to document neural or neuroendocrine differentiatial diagnosis of metastatic lesions such as neuroblastoma, paraganglioma and other neuroendocrine tumors.
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