Patients who had histories of skin or thyroid cancers
were excluded. Patients with primary head or neck cancers
were surgically treated after the detection of lung metastases
on chest roentgenograms or computed tomography (CT)
scans. We excluded patients with distant metastases other
than pulmonary metastases, or those who were suspected to
have carcinomatous lymphangiosis detected on CT scans.
The disease-free interval (DFI) is defined as the period
between initial treatment of a primary tumor and the resection of one or more pulmonary metastases. Overall survival(OS) was measured between the date of pulmonary resection
to the date of death from any cause, or the latest date on which
the patient was known to be alive.