Immunohistochemical differentiation of metastatic tumours

Immunohistochemistry is a powerful tool for classifying poorly differentiated cancers and metastatic tumours of unknown origin. Many useful immunohistochemistry stains target proteins unique to a particular organ or cell type, and examples of this group include thyroglobulin for thyroid follicular cells, and surfactant proteins for pulmonary type II pneumocytes and Clara cells. These proteins are closely related to the ultimate function of the particular cell type, and they are more likely expressed by well-differentiated tumours but not poorly differentiated ones. Transcription factors generally function to determine the fate of specification and differentiation in precursor cells, and absence of one transcription factor might result in agenesis of the particular organ and tissue. Due to its role in precursor cells, they are likely to be expressed even in poorly differentiated or undifferentiated tumours. This review article will discuss the combined application of differentiation markers as well as transcription factors to metastatic tumours.