The "Classification Pendulum" of Stage I Colorectal Cancer: A National Level Analysis of the Survival Difference Between T1 and T2 Colorectal Cancer

BACKGROUND: The eighth edition of the American Joint Committee on Cancer classifies nonmetastatic, node-negative colorectal cancers invading the submucosa (T1) and muscularis propria (T2) as stage I tumors without additional subclassification. OBJECTIVE: The aim of the study was to compare survival of T1N0M0 versus T2N0M0 colorectal cancers and to investigate factors associated with decreased survival. DESIGN: This was an analysis of 2 large population-based data sets. SETTINGS: The study was conducted analyzing data from the Surveillance Epidemiology and End Result program and the National Cancer Database. PATIENTS: Adult patients undergoing major resection without additional therapy for stage I colorectal cancer were included. MAIN OUTCOME MEASURES: Overall and disease-specific survival for T1 versus T2 cancers were measured. Subgroup analyses by tumor location (colon versus rectum) were performed. RESULTS: A total of 30,228 (36.4% T1 and 63.6% T2) and 41,670 (41.1% T1 and 58.9% T2) patients were identified in the Surveillance Epidemiology and End Result database and the National Cancer Database. The 5-year overall survival rates were 87.1% and 86.2% for patients with T1 versus 82.7% and 80.7% for patients with T2 (p < 0.001) in the Surveillance Epidemiology and End Result database and the National Cancer Database. The 10-year overall survival rates were 71.3% and 66.3% for patients with T1 versus 62.2% and 57.2% for patients with T2 tumors (p < 0.001) in the Surveillance Epidemiology and End Result database and the National Cancer Database. The 5- and 10-year disease-specific survival for colorectal cancer in the Surveillance Epidemiology and End Result database was 97.0% (T1) versus 95.2% (T2) and 94.1% (T1) versus 90.3% (T2). Black race (HR = 1.26 and 1.65 for overall survival and disease-specific survival in the Surveillance Epidemiology and End Result database; HR = 1.20 for overall survival in the National Cancer Database) was associated with worse survival. LIMITATIONS: The study was limited by intrinsic biases related to large administrative data sets. CONCLUSIONS: Within stage I colorectal cancer, T2 tumors have decreased overall survival and disease-specific survival as compared with T1 cancers. This survival difference may justify revising the American Joint Committee on Cancer staging system to include the subclassification of stage Ia (T1N0M0) and stage Ib (T2N0M0).