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Previous studies have shown that the AJCC Cancer Staging Manual, 7th edition (AJCC 7), tumor classification for cutaneous squamous cell carcinoma (CSCC) failed to accurately stratify disease-related outcomes. The recently released 8th edition (AJCC 8) features a revised tumor classification for only head and neck CSCC (HNCSCC).To compare AJCC 7 and AJCC 8 tumor classifications for HNCSCC and to validate AJCC 8.This was a 10-year retrospective cohort study (2000-2009) at an academic tertiary care center reviewing 680 primary HNCSCC tumors in 459 patients.Primary HNCSCC tumors were reviewed for disease-related outcomes (DROs): local recurrence (LR), nodal metastasis (NM), and disease-specific death (DSD). Tumors were stratified by AJCC 7 and AJCC 8 tumor classification. Distinctiveness (outcome differences between categories), homogeneity (outcome similarity within categories), and monotonicity (outcome worsening with increasing categories) were assessed for both classifications.Most of the 459 patients were white (451 [98.3%]) and male (312 [68.0%]). AJCC 8 high tumor categories (T3/T4) accounted for 121 (17.8%) of total cases but 50 of 71 DROs (70.4%) (22 of 34 of LRs [64.7%], 17 of 24 NMs [70.8%], and 11 of 13 of DSDs [84.6%]). This was a significant improvement over AJCC 7, where only 12 of 71 DROs (16.9%) (4 of 34 LRs [11.8%], 3 of 24 NMs [12.5%], and 5 of 13 DSDs [38.5%]) occurred in T3/T4 categories. However, AJCC 8 T2 and T3 were indistinct, with overlapping 95% CIs for 10-year cumulative incidences of LR, NM, and DSD. The 10-year cumulative incidence of DROs in the 119 AJCC 8 T3 cases were 19.7% (95% CI, 13.0%-29.7%) for LR, 14.1% (95% CI, 9.7%-20.7%) for NM, and 9.3% (95% CI, 6.8%-14.0% for DSD).AJCC 8 demonstrates superior homogeneity and monotonicity compared with AJCC 7. It now may be possible for AJCC 8 HNCSCC T2, T3, and T4 cases to be recorded and tracked by tumor registries because they represented a 23.1% subset in this study, which includes nearly all poor outcomes (85.9%). Further work is needed to validate AJCC 8 with population-level data and to compare AJCC 8 performance against alternative tumor classifications.