Evaluation of AJCC and an Alternative Tumor Classification System for Primary Vulvar Squamous Cell Carcinoma

Background: Currently, no studies have attempted to validate the AJCC tumor (T) class for vulvar cancer or examine its performance via clinical data. The goal of this study was to identify risk factors associated with poor outcomes in vulvar squamous cell carcinoma (vSCC) and compare prognostic discrimination of these outcomes between the AJCC T-classification system and the newly developed Brigham and Women's Vulvar Tumor Classification system (BWVTC). Methods: A 15-year, 2-center retrospective cohort study of primary vSCCs (N=226) was undertaken. Risk factors for poor outcomes, including local recurrence (LR), nodal and distant metastasis (NM and DM, respectively), disease-specific death (DSD), and overall death (OD) were determined using competing risks models. Poor outcomes were analyzed by T stage with regard to each classification system's distinctiveness, homogeneity, and monotonicity. Results: AJCC T stages were indistinct, with overlapping 95% confidence intervals for 10-year cumulative incidences of poor outcomes. Most poor outcomes occurred in low AJCC T stages: T1a/T1b contained 77% of LR, 79% of NM, 66% of DM/DSD, and 78% of OD, indicating poor homogeneity and monotonicity. Five risk factors were independent predictors of poor outcomes: history of lichen sclerosus, tumor diameter ≥2.0 cm, tumor depth ≥3.0 mm, poor differentiation, and mucosal involvement, and these were used to develop the BWVTC (BWVTC BWT1 = 0 risk factors; BWT2 = 1 risk factor; BWT3 = 2 risk factors; and BWT4 = ≥3 risk factors). The BWVTC displayed superior homogeneity and monotonicity, with most poor outcomes occurring in high T stages: T3/T4 contained 87% of LR, 92% of NM, 91% of DM/DSD, and 78% of OD (P<.001), although not all T stages were statistically distinct in this small cohort. Conclusions: The BWVTC offers improved prognostic discrimination over the AJCC T-classification system. Validation in population-based cohorts and in vulvar cancers other than SCC is needed.