Performance of Staging Systems for Non-head and Neck Cutaneous Squamous Cell Carcinoma

Data are limited regarding the performance of staging systems for non-head and neck cutaneous squamous cell carcinomas (non-HNCSCCs).

The aim of this study was to evaluate the performance of the Brigham and Women's Hospital (BWH) and American Joint Committee on Cancer 8th edition (AJCC8) staging system in predicting poor outcomes in non-HNCSCCs.

Demographics, tumor features and stages, and outcomes for non-HNCSCCs were collected retrospectively from 11 institutions in two countries. Poor outcomes included local recurrence, metastasis, and disease-specific death; major poor outcomes excluded local recurrence. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), concordance index (c-index), and 3-year cumulative incidence were calculated. Cumulative incidence function (CIF) plots were created.

9300 non-HNCSCCs were included. Ninety-five tumors (1%) resulted in major poor outcomes; 250 (2.7%) resulted in poor outcomes. The rate of local recurrence was 1.9%, and the rate of nodal metastasis was 0.74%. Major poor outcomes were predicted with sensitivities 0.48/0.49, specificities 0.98/0.96, PPVs 0.17/0.13, NPVs 0.99/0.99, and c-indices 0.73/0.74 for BWH/AJCC8. Poor outcomes were predicted with sensitivities 0.24/0.26, specificities 0.98/0.97, PPVs 0.22/0.17, NPVs 0.98/0.98, and c-indices 0.61/0.61 for BWH/AJCC8.

Both systems performed similarly in predicting poor outcomes in non-HNCSCCs. Specificity and NPV were high, sensitivity and PPV were low, and c-indices were moderately high. As the c-indices were comparable to those seen in the HNCSCC literature, it is reasonable to use the BWH and AJCC8 staging systems for tumors located off the head and neck. However, further refinement of CSCC staging systems is needed to improve prognostication.