Background: We evaluated the heterogeneity of primary tumor volume (PTV) within tumors of the same pT4a-staged tongue carcinoma and to elucidate the effects of PTV on treatment outcomes in patients with pT4a-staged tongue carcinoma. Methods: Fifty-eight patients with newly diagnosed pT4a-staged tongue carcinoma who received surgery were enrolled onto this study. Magnetic resonance imaging-derived PTV was measured by the summation-of-area technique. Results: The mean PTV was 24.55 ml, with a range of 5.32 to 119.64 ml. The receiver operating characteristic curve was applied, and the optimal cutoff volume was 23 ml. Large PTV was associated with a significantly poor disease-specific survival (P = 0.010) by the log rank test. The Cox regression model also revealed that large PTV (P = 0.026) and positive lymphatic node metastasis (P = 0.004) were statistically significant in the prognosis of T4a-staged tongue carcinoma. Conclusions: A substantial variation of PTV was present within the same pT4a-staged tongue carcinoma, and PTV represented an important prognostic factor. In the light of these findings, we suggest that taking the PTV into account in pT4a-staged tongue carcinoma would better refine the newest revised T classification, and the treatment strategies may be different.
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