Validation of the 9th Edition of the UICC TNM classification and the prognostic impact of nodal spread in salivary gland cancer

Background: The 9th edition of the UICC TNM classification redefined N categories and clinical stages for salivary gland cancer (SGC). We validated the prognostic utility of this redefinition and evaluated the impact of anatomical nodal spread. Methods: We retrospectively analyzed 166 patients with SGC and 93 parotid gland cancer (PGC) patients treated with curative surgery. Cases were restaged according to the TNM classification of the UICC 9th edition. Kaplan–Meier survival curves, Cox models, and statistical indices (AIC, likelihood ratio χ², C-index) were used to compare the findings based on the 8th and 9th editions. Nodal metastases were classified as “Intraparotid lymph nodes (LNs) only”, “Limited to levels I–III LNs”, and “Beyond levels I–III LNs”. Results: Kaplan–Meier curves showed clearer separation by N category and clinical stage for the 9th edition, although its prognostic performance by statistical indices was similar to that of the 8th edition. In the PGC surgery subset, LN metastasis, particularly N2 in the 9th edition, was the strongest adverse prognostic factor, and the new 9th edition pathological N categories were also useful. Additionally, prognosis worsened with increasing nodal extent. Twelve patients with metastases beyond levels I–III developed distant metastases despite standard treatment, and 10 with salivary duct carcinoma, indicating potential benefit from adjuvant systemic therapy. Conclusions: Kaplan–Meier analyses suggested that the 9th edition provided better intercategory discrimination than the 8th edition, despite no statistical superiority being demonstrated. Nodal metastasis extending beyond levels I–III may be a useful biomarker for selecting patients for adjuvant systemic therapy.