## TNM Staging of Oral Cavity Carcinoma (AJCC 8th Edition) **Key Point:** The T (tumor) stage in oral cavity carcinoma is primarily based on the greatest dimension of the primary tumor, measured in centimeters. The T2 stage specifically refers to tumors >2 cm but ≤4 cm. ### TNM T-Stage Classification for Oral Cavity Carcinoma | T Stage | Size Criteria | Description | |---|---|---| | T1 | ≤2 cm | Tumor confined to site of origin; depth of invasion (DOI) ≤5 mm | | T2 | >2 cm but ≤4 cm | Tumor >2 cm but ≤4 cm; DOI ≤10 mm | | T3 | >4 cm OR DOI >10 mm | Tumor >4 cm in greatest dimension OR depth of invasion >10 mm (regardless of size) | | T4a | Moderately advanced | Tumor invades adjacent structures (bone, muscle, maxillary sinus, skin) | | T4b | Very advanced | Tumor invades masticator space, pterygoid plates, or skull base | | TX | Cannot assess | Primary tumor cannot be assessed | **High-Yield:** The **depth of invasion (DOI)** is increasingly important in modern staging. A tumor ≤2 cm with DOI >5 mm may be upstaged, and any tumor with DOI >10 mm is classified as at least T3, regardless of surface size. **Clinical Pearl:** The shift from purely size-based staging to inclusion of depth of invasion reflects improved prognostic accuracy. A small superficial tumor has better prognosis than a small but deeply invasive tumor. **Mnemonic:** **T-Size Rule** — T1 (≤2 cm), T2 (>2–4 cm), T3 (>4 cm or DOI >10 mm). Remember: **Depth matters as much as size** in modern staging. 
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