Real-world multicenter evaluation of the AJCC TNM-9 staging for oral minor salivary gland carcinomas

The 8th edition AJCC TNM (TNM-8) staging framework frequently lacks distinct prognostic discrimination for minor salivary gland carcinomas (mSGCs). This multicenter study was designed to validate the proposed 9th edition (TNM-9) classification, which is tailored to better reflect the biology of these tumors, specifically in oral mSGCs. We conducted a retrospective cohort study encompassing 163 patients with primary oral mSGCs treated with curative intent across four tertiary cancer centers. All cases were re-staged using both TNM-8 and the proposed TNM-9 criteria. The primary endpoint was disease-specific survival (DSS). System performance was compared using the Harrell C-index, Akaike Information Criterion (AIC), categorical Net Reclassification Improvement (NRI), and Decision Curve Analysis. Under the TNM-9 system, survival curves for DSS showed clear and statistically significant separation across all stage groups ( p < 0.001). In contrast, TNM-8 failed to significantly differentiate between Stage III and Stage IV outcomes. Advanced TNM-9 stages (IIIA and IIIB) were strong independent predictors of worse DSS. TNM-9 demonstrated superior discriminative ability compared to TNM-8 (C-index: 0.74 vs. 0.68) and a better model fit (AIC: 460 vs. 485). Additionally, TNM-9 correctly reclassified 23% of patients (NRI = 0.23; p = 0.002) and yielded consistently higher clinical net benefit. The proposed TNM-9 classification showed better prognostic discrimination, model fit, and risk reclassification than TNM-8 within this retrospective multicenter cohort. External validation of TNM-9 in larger, geographically diverse cohorts with longer follow-up is required before its routine clinical adoption.