Diagnostically Relevant Molecular Markers in Head and Neck Neoplasms

Tumor markers are grouped into diagnostic and prognostic markers. Specific diagnostic markers appear extensively in cells of a particular neoplasm and not in other tumors. These markers can be used to assess the cellular lineage and histogenic origin of various neoplasms. Thus, diagnostic markers can be used for the confirmatory diagnosis of various tumors. This paper reviews the literature on various diagnostic markers and aims to group them based on the cellular lineage of neoplasms. 1. Introduction Tumor markers are proteins produced by the tumor cells or by other cells of the body in response to cancer or certain benign (noncancerous) conditions. These substances can be found in the blood, in the urine, in the tumor tissue, or in other tissues. Different tumor markers are found in different types of cancer, and levels of the same tumor marker can be altered in more than one type of cancer [1]. Tumor markers can be categorized into diagnostic and prognostic markers. Antigens or clusters of antigens expressed by the tumors can be detected with the help of specific diagnostic investigations [1]. Based on the expression, the diagnostic markers can be classified into mesenchymal marker, epithelial markers, markers for muscle differentiation and neural differentiation, vascular markers, and markers for melanin, histiocytes, and leukocytes. Even the most perplexing round cell tumors, spindle cell tumors, and carcinosarcoma can be distinguished with the help of specific diagnostic markers. Prognostic markers can determine the growth, metastasis, and invasion potential of tumor. Common methods used to identify tumour-related protein include immunohistochemistry, fluorescent in situ hybridization (FISH), and reverse transcriptase-polymerase chain reaction. Immunohistochemistry is one of the methods wherein the antibody-based reagent is used for the localization of specific epitopes in tissue sections to detect the histogenic origin of the tumor. RT PCR enzymatic reaction with reversed transcriptase can be used to assess gene expression and micrometastasis in tumour [2]. 2. Diagnostic Markers for Tumors with Muscle Cell Differentiation 2.1. Desmin Desmin is a type III intermediate filament found near the Z line in sarcomeres. It is a 52？kD protein that is a subunit of intermediate filaments in skeletal muscle tissue, smooth muscle tissue, and cardiac muscle tissue. Its presence in vascular smooth muscle is variable [3]. The muscle cell matures only if desmin is present. Vimentin is present in higher amounts during embryogenesis while desmin is present in