Validation of the ninth edition pathological and clinical TNM classifications for salivary gland carcinoma

OBJECTIVES: To validate the performance of pathological and clinical UICC 9th edition/AJCC Version 9 (TNM9) classifications in salivary gland carcinoma (SGC). METHODS: Patients with newly diagnosed major or minor SGC treated between 2006 and 2021 were retrospectively reviewed. Cases were restaged using pathological and clinical TNM8 and TNM9 criteria to compare 5-year disease-free survival (DFS) across both stage classifications. TNM9 restaging incorporated re-review of pre-treatment CT/MRI and pathology to assess lymph node (LN) number and extranodal extension (ENE). RESULTS: Among 402 patients (282 major, 120 minor SGCs), DFS did not differ between major and minor tumors (p = 0.322). Median follow-up was 5.4 years. Under TNM8, pN categories showed paradoxical 5-year DFS for N1 vs N2a (58 % vs 67 %), although stage stratification remained acceptable (I/II/III/IVA-B: 97 %/88 %/64 %/40 %). For TNM9 assessment, radiologic-pathologic concordance for LN count was moderate (Kappa = 0.600). Imaging-detected ENE demonstrated high specificity (99 %) but low sensitivity (30 %) for pathologic ENE. TNM9 improved DFS separation by pN category (N0/N1/N2: 83 %/55 %/27 %) and stage (I/II/IIIA/IIIB: 97 %/88 %/61 %/33 %), with a slightly higher C-index (0.822 vs 0.817). TNM8 cN categories showed limited discrimination for DFS between cN1 vs cN2a (53 % vs 50 %), while TNM9 cN did not clearly distinguish cN1 from cN2 (36 % vs 42 %). Nonetheless, cTNM8 (I/II/III/IVA-B: 94 %/87 %/62 %/47 %) and cTNM9 stage (I/II/IIIA/IIIB: 94 %/87 %/58 %/40 %) both showed acceptable discrimination in DFS, with comparable C-indices (0.804 vs 0.808). CONCLUSIONS: Similar outcomes between major and minor SGCs support their unification in TNM9. While pTNM9 classification improves prognostic discrimination over pTNM8, cN-category performance remains suboptimal, likely reflecting moderate radiologic-pathologic concordance in LN assessment.