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.