Tumor Site Descriptions
Oral Cavity:
Mucosa of lip, Tongue (border, surface, or anterior 2/3), Upper or lower gum, Floor of mouth, Hard palate, Cheek mucosa, Retromolar area
Oropharynx, Base of tongue, Tonsil, Soft palate, Uvula, Vallecula
Hypopharynx, Pyriform sinus
Nasopharynx (Superior, posterior, lateral, or anterior wall)
Larynx (Glottis, subglottis, supraglottis, or laryngeal cartilage), Anterior surface of epiglottis

Tumor Extension Descriptions (Oral Cavity and Oropharynx)
Tumor is confined to primary site of origin
Extension, not T4:
Tumor extends beyond site of origin, but does not extend to the regions that would classify it as T4a or T4b (see below)
Extension, T4a:
Tumor invades through bone, to deep/extrinsic muscles of tongue, to maxillary sinus or skin of face (oral cavity), or to medial pterygoid or hard palate (oropharynx)
Extension, T4b:
Tumor encases internal carotid artery or invades skull base, pterygoid plates, masticator space (oral cavity), or lateral pterygoid muscle or lateral nasopharynx (oropharynx)