Limitations
This study did not include data concerning the HPV status of patients.
Positive HPV status may suggest a different prognosis for head and neck
squamous cell carcinoma. Perhaps more importantly information regarding
the treatment methods of patients was unavailable. Different treatment
methods may affect the survival of patients. Finally, the SEER database
includes only patients from the United States; different countries may
result in different tumor prognosis. For the aforementioned reasons our
findings may have resulted in an underestimation of our results.