Diagnosis of metastatic neoplasms: an immunohistochemical approach.

CONTEXT: It is important to determine the type and/or site of origin of metastatic tumors for optimal clinical management.

OBJECTIVE: To summarize the use of currently available immunohistochemical markers in the evaluation of metastatic tumors.

DATA SOURCES: Review of relevant literature on immunohistochemical evaluation of tumors and the author's personal experience.

CONCLUSIONS: Immunohistochemistry is an important ancillary technique for evaluation of metastatic tumors and should be used in the context of routine morphology and clinical information. While a single marker may be used to support a known or suspected site of origin, a carefully constructed panel is strongly recommended, particularly for tumors of morphologically uncertain lineage or origin.