Table 7:

Oral cavity primary tumor definitions^a

T Category	T Criteria
Tx	Primary tumor cannot be assessed
Tis	Carcinoma in situ
T1	Tumor ≤2 cm, ≤5-mm DOI; DOI is depth of invasion and not tumor thickness
T2	Tumor ≤2 cm, DOI >5 mm and ≤10 mm or tumor >2 but ≤4-cm and ≤10-mm DOI
T3	Tumor >4 cm or any tumor >10-mm DOI
T4a	Moderately advanced local disease; tumor invades adjacent structures only (eg, through cortical bone of the mandible or maxilla or involves the maxillary sinus or skin of the face); note that superficial erosion of bone/tooth socket (alone) by a gingival primary is not sufficient to classify a tumor as T4
T4b	Very advanced local disease; tumor invades masticator space, pterygoid plates, or skull base and/or encases the internal carotid artery

^aNote that the greatest diameter of the primary tumor is still measured, but primary tumor depth of invasion is also a critical determinant of T-staging. This is the deep extent of tumor invasion below the surface and is distinct from tumor thickness. Lip tumors are no longer staged along with oral cavity SCC, but using the tables from “Cutaneous Carcinoma of HN.” Table adapted with permission of the American Joint Committee on Cancer, Chicago, Illinois. The original source for this material is the AJCC Cancer Staging Manual.¹