Distant metastases from head and neck squamous cell carcinoma. Part I. Basic aspects.

The incidence of distant metastasis in head and neck squamous cell carcinoma (HNSCC) is relatively low but remains a major determinant of prognosis and therefore an important factor in clinical decision making. The most frequently involved sites for distant metastasis are the lung (approximately 70% of cases), followed by bone and liver. There are often conflicting reports on which parameters are risk factors for distant metastasis, but the most important predictive factors appear to be the site of the primary tumor (hypopharynx in particular), advanced T- and N-classification, histological grade and the ability to achieve locoregional disease control. Metastasis results from a selection of tumor cells that have acquired the properties to withstand multiple and often unfavorable circumstances and settle in distant organs. Most of these processes involve interaction between tumor cells, their microenvironment and host factors. Increasing knowledge of the biology of distant metastasis may result in the development of diagnostic and therapeutic strategies targeted to this usually terminal stage for patients with HNSCC.