Participants
All adult (age > 18) patients with advanced (T4a or T4b) OCSCC diagnosed from 2007 to 2016 were included. 2007 was chosen as a starting point for our population based on the timing of SEER’s collection of information on patient insurance status. Patients were identified based on combinations of variables including tumor histology -squamous cell carcinoma and its variants (basaloid, papillary, spindle cell, verrucous), primary site – mucosal lips (C000-C006, C008-C009); oral tongue (C020-C024, C028-C029); floor of mouth (C040-C049); and gum and other mouth (C030-C039, C050-C059, C060-C069)], and stage- T4, T4a, and T4b. Tumors of the base of tongue and any subsite that included or overlapped with the oropharynx were excluded to prevent confounding or effect modification by human papillomavirus virus (HPV) infection. The following exclusion criteria were used: patients with unknown demographic information including sex, age at diagnosis, race, and marital status; patients with unknown clinical information including histologic grade, AJCC Tumor, Node, Metastasis (TNM) stage; patients with no information on definitive surgery or radiotherapy; and patients with metastatic disease at initial presentation.