266 Background: The 7th AJCC T-stage classification system for adrenocortical carcinoma (ACC), based on size and extra-adrenal invasion, does not adequately stratify patients by survival. Lymphovascular invasion (LVI) is a known poor prognostic factor. We propose a novel T-stage system that incorporates LVI to better risk-stratify patients undergoing resection for ACC. Methods: Patients undergoing curative-intent resections for ACC from 1993-2014 at 13 institutions comprising the US ACC Study Group were included. Primary outcome was disease-specific survival (DSS). Results: Of 265 patients with ACC, 149 had complete data for analysis. The current T-stage system failed to differentiate patients with T2 vs T3 disease ( p= 0.10). Presence of LVI was associated with worse DSS compared to no LVI (36 vs. 168mos; p= 0.001). After accounting for the individual components of the current T-stage system (size and extra-adrenal invasion), LVI persisted as a poor prognostic factor on multivariable analysis (HR 2.14, 95% CI 1.05-4.38, p= 0.04). LVI positivity further stratified patients with T2 and T3 disease, (T2: 37mos vs median not reached; T3: 36 vs 96mos; p =0.03), but did not influence survival in patients with T1 or T4 disease. By incorporating LVI, a new T-stage classification system was created: [T1: < 5cm, (-)local invasion, (+/-)LVI; T2: > 5cm, (-)local invasion, (-)LVI OR any size, (+)local invasion, (-)LVI; T3: > 5cm, (-)local invasion, (+)LVI OR any size, (+)local invasion, (+)LVI; T4: any size, (+)adjacent organ invasion, (+/-)LVI]. Each progressive new T-stage group was associated with worse median DSS (T1: 167mos; T2: 96mos; T3: 37mos; T4: 15mos; p< 0.001). Conclusions: The current AJCC T-stage system for ACC does not adequately stratify patients by survival, particularly for T2 and T3 disease. The proposed T-stage classification system, which incorporates lymphovascular invasion, better differentiates T2 and T3 disease and accurately stratifies patients by disease-specific survival. If externally validated, this novel T-stage classification should be considered for future AJCC staging systems.
A Novel T-Stage Classification System for Adrenocortical Carcinoma: Proposal from the U.S. Adrenocortical Carcinoma Study Group