Concise immunohistochemistry in carcinoma of unknown primary origin

Abstract

Carcinoma of unknown primary origin is a malignant epithelial neoplasm clinically defined by the presence of metastasis without known primary origin at the time of diagnosis. When it is clinically encountered, further investigations should be considered. Identification of primary origin of such neoplasm is crucial for proper patient management and prognosis. Immunohistochemistry has become an ancillary study for resolving this issue. Initial
immunohistochemistry panel including AE1/AE3, S100, CD45 and vimentin is suggested for identification of lineage of tumor cell differentiation. If the tumor cells are diffusely positive for AE1/AE3 confirming the diagnosis of carcinoma, additional immunohistochemistry markers including CK7, CK20 and other tissue-specific markers should be employed in order to determine a primary origin. Interpretation of immunohistochemistry should always be correlated with histopathological findings, clinical context and radiological information. This approach can facilitate determination of the type and origin of carcinoma of unknown primary origin.