Comparative assessment of the eighth and seventh AJCC staging edition prognostic performance of patients with p16 positive oropharynx cancer.

Abstract

6067 Background: The American Joint Committee on Cancer (AJCC) TNM staging system defines the anatomical extent of disease and serves as a guide for treatment and prognosis. The favorable prognosis of p16+ oropharyngeal squamous cell carcinoma (OPSCC) compared to p16 negative counterpart led to major updates in the AJCC 8th edition. Its prognostic performance, however, warrants further validation. Methods: We included patients diagnosed with p16+ OPSCC enrolled in a prospective registry ( Stiefel) at The University of Texas MD Anderson Cancer Center between March 2015 and December 2018. Patients’ stage at diagnosis was classified according to the AJCC 7th (AJCC-7) and 8th (AJCC-8) editions. Overall survival (OS) and progression-free survival (PFS) was defined as time from diagnosis to death or to progression or death, respectively. The Kaplan-Meier method was used to calculate 1- and 3-year survival probabilities. Differences between groups were compared using the log-rank test. Prognostic discriminative performance of each staging system was evaluated using Harrel’s C-statistic. Survival differences between heavy (> 10 pack-years [PY]) vs. light/never smokers (≤ 10 PY) by AJCC-8 staging groups was assessed with the log-rank test. Results: Of 463 patients, the median follow-up was 34.7 months (2.3-169.74). Nearly 90% (N=413) of patients were down-staged from AJCC-7 to AJCC-8 with 69% of patients with IVA disease based on AJCC-7 (N=319) re-staged as stage I (N=196 [42%]), II (N=79 [17%]) or III (44 [10%]) according to AJCC-8. Over 60% (N=279) of patients were staged as I with AJCC-8. Compared to AJCC-7, AJCC-8 had improved prognostic ability (C-statistic, 0.58 for AJCC-7 vs. 0.63 for AJCC-8) and provided better discriminative survival probabilities at 1 and 3-year follow-up (Table). Similar results were observed for PFS. Smoking status did not impact OS when stratified by AJCC-8 staging groups: I, p=0.347; II, p=0.310; and III, p=0.532 for > 10 vs. ≤ 10 PY. Conclusions: Our cohort validates that the AJCC-8 provides better prognostic discriminative performance when compared to AJCC-7, however, a disproportionate number of patients were classified as stage I. Smoking was not associated with survival within each staging group.[Table: see text]