<qa>  What is the primary site of squamous cell carcinoma of the head and neck?Patients with histologically or cytologically documented squamous cell carcinoma of the head and neck SCCHN eligible primary sites: oral cavity, oropharynx, hypopharyx, or larynx presenting with locally recurrent andor metastatic disease, with at least 1 unidimensionally or bidimensionally measurable lesion. 