Clinical Outcomes in pT4 Tongue Carcinoma are Worse than in pT3 Disease: How Extrinsic Muscle Invasion Should be Considered?

ABSTRACT

BACKGROUND: The identification of extrinsic tongue muscle invasion in oral cavity cancer remains challenging. Notably, the most recent American Joint Committee on Cancer (AJCC 2017, 8th edition) staging manual indicates that extrinsic muscle invasion does not lead to the diagnosis of a T4 tumor. Because this approach carries the risk of tumor downstaging, we compared the clinical outcomes of patients with oral tongue squamous cell carcinoma (SCC) staged as pT3 vs. pT4 according to the AJCC 2010, 7th edition criteria. METHODS: We retrospectively examined the records of consecutive patients with pT3 (n = 135) and pT4 (n = 68) tongue SCC who underwent radical surgery. Of the 68 pT4 tongue SCC, 63 (93%) had extrinsic muscle involvement alone. The 5-year locoregional control (LRC), distant metastasis (DM), and disease-free survival (DFS) rates served as outcome measures. RESULTS: Compared with pT3 tongue SCC, pT4 patients presented significantly more frequently with pN2 disease, extranodal extension, poor tumor differentiation, tumor depth >15 and >20 mm, margin status ≤4 mm, perineural invasion, vascular invasion, and were more frequently treated with surgery plus concurrent chemoradiotherapy. Less favorable 5-year outcomes were observed in patients with pT4 than pT3 tumors (LRC 50 vs. 75%, p < 0.001; DM 27 vs. 14%, p = 0.013; DFS 43 vs. 69%, respectively, p < 0.001). We identified pT4 disease (vs. pT3) as an independent adverse prognostic factor for LRC and DFS. CONCLUSIONS: We suggest classifying patients with tongue SCC and extrinsic muscle invasion as having pT4 disease.