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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. 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. 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). 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.

Regional nodal metastases from cutaneous squamous cell carcinoma (cSCC) is strongly associated with a poor prognosis, but these metastases are difficult to predict clinically. Sentinel node biopsy (SNB) has been used for a wide range of malignancies to assess for regional nodal metastasis, but is not widely used for cSCC. Patients presenting with high-risk cSCC of the head and neck with clinically N0 necks were offered SNB at the time of primary cSCC excision or secondary wide local excision. Patients with positive sentinel nodes were offered completion lymph node dissection, and all the patients were followed up at regular intervals for up to 5 years. In this study, 105 lesions underwent SNB, and 10 sentinel nodes (9.5%) were positive. In an additional five patients, regional recurrence developed after a negative sentinel node, with a total subclinical nodal metastasis rate of 14.3%. Nodal metastases were significantly associated with reduced disease-specific survival. The significant predictors of metastasis were four or more high-risk features or tumors with a concurrent invasion deeper than 5 mm and PNI. For high-risk cSCC, SNB is a safe and feasible staging technique. The total number of high risk features and certain combinations of high-risk features predicted metastasis better than individual high-risk features.