ABSTRACT: Importance: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). Objective:To compare AJCC 7 and AJCC 8 tumor classifications for HNCSCC and to validate AJCC 8. Design, Setting, and Participants:This was a 10-year retrospective cohort study (2000-2009) at an academic tertiary care center reviewing 680 primary HNCSCC tumors in 459 patients. Main Outcomes and Measures: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. Results: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). Conclusions and Relevance: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.
