Background: The American Joint Committee on Cancer (AJCC) uses the same nodal staging system for cutaneous and mucosal squamous cell carcinoma of the head and neck in its 8th edition (AJCC 8) despite differences in the etiology, risk factors, and clinical behavior of the two diseases. This study aims to evaluate the performance of the AJCC 8 nodal staging system by direct comparison of cutaneous (cSCC) versus oral squamous cell carcinoma (oSCC) patients.
Methods: Patients with metastatic cSCC (N = 382) and oSCC (N = 325) were identified from a prospective database (years 1987-2016). Multivariable analysis was performed using Cox proportional hazards competing risk model. To assess staging system performance, an explained variation measure (proportion of variation explained, PVE) as well as a discrimination measure (Harrell's concordance index, C-index) were used.
Results: Inclusion of extranodal extension (ENE) in AJCC 8 increased the proportion of patients in N3b category (48.7% in cSCC, 40.3% in oSCC). AJCC 8 stratified poorly with regards to risk of death from cSCC and oSCC and showed limited monotonicity of the nodal categories. Estimates of model performance revealed modest predictive capacity for overall survival (OS) and disease-specific survival (DSS) in oSCC (Harrell's C of 0.66 in both) and weak predictive capacity in cSCC (Harrell's C of 0.58 and 0.61, respectively).
Conclusions: The AJCC 8 nodal staging system performs poorly in terms of stratifying survival by N category, especially in cSCC. The data indicate that cSCC merits an independent nodal staging system from that for mucosal SCC.