Metastases of unknown primary site.

Despite the fact that effective therapy does not currently exist for the majority of patients presenting with metastases of unknown primary site, the last decade has witnessed significant advances in the approach to this heterogeneous disease. The use of modern pathologic techniques that frequently provide better diagnostic precision and the recognition of specific subgroups with a favorable prognosis and responsiveness to treatment has improved the outcome for some patients. Currently the diagnostic strategy should emphasize the rapid identification of patients likely to benefit from available therapy, whereas clinical research should focus on the development of more effective treatments for those patients with unresponsive tumors. In the future, continued improvements in the molecular characterization of these tumors will likely enhance understanding of the metastatic process, allow for more specific definitions of cell lineage, and provide insights for better therapy.