A National-Level Validation of the New American Joint Committee on Cancer 8th Edition Subclassification of Stage IIA and B Anal Squamous Cell Cancer

Introduction The 8th edition of the American Joint Committee on Cancer (AJCC) updated the staging system of anal squamous cell cancer (ASCC) by subdividing stage II into A (T2N0M0) and B (T3N0M0) based on a secondary analysis of the RTOG 98-11 trial. We aimed to validate this new subclassification utilizing two nationally representative databases. Materials The National Cancer Database (NCDB) [2004–2014] and the Surveillance, Epidemiology, and End Results (SEER) database [1988–2013] were queried to identify patients with stage II ASCC. Results A total of 6651 and 2579 stage IIA (2–5 cm) and 1777 and 641 stage IIB (> 5 cm) patients were identified in the NCDB and SEER databases, respectively. Compared with stage IIB patients, stage IIA patients within the NCDB were more often females with fewer comorbidities. No significant differences were observed between age, race, receipt of chemotherapy and radiation, and mean radiation dose. Demographic, clinical, and pathologic characteristics were comparable between patients in both datasets. The 5-year OS was 72% and 69% for stage IIA versus 57% and 50% for stage IIB in the NCDB and SEER databases, respectively ( p < 0.001). After adjustment for available demographic and clinical confounders, stage IIB was significantly associated with worse survival in both cohorts (hazard ratio 1.58 and 2.01, both p < 0.001). Conclusion This study validates the new AJCC subclassification of stage II anal cancer into A and B based on size (2–5 cm vs. > 5 cm) in the general ASCC population. AJCC stage IIB patients represent a higher risk category that should be targeted with more aggressive/novel therapies.