Revised TN categorization for colon cancer based on national survival outcomes data

Purpose: The sixth edition of American Joint Committee on Cancer (AJCC) Cancer Staging Manual for colon cancer subdivided stage II into IIA (T3N0) and IIB (T4N0) and stage III into IIIA (T1-2N1M0), IIIB (T3-4N1M0), and IIIC (anyTN2M0). Subsequent analyses supported revised substaging of stage III because of improved survival for T1-2N2 versus T3-4N2 and T4N1 survival was more similar to T3-4N2 than to T3N1. The AJCC Hindgut Taskforce sought population-based validation that depth of invasion and nodal status interact to affect survival. Patients and Methods: Surveillance, Epidemiology, and End Results (SEER) population-based data from January 1992 to December 2004 for 109,953 colon cancer patients were compared with National Cancer Data Base (NCDB) data on 134,206 patients. T4N0 cancers were stratified by tumors that perforate visceral peritoneum (T4a) versus tumors that invade or are adherent to adjacent organs or structures (T4b). N1 and N2 were stratified by number of involved positive lymph nodes (N+): N1a/N1b (1 v 2-3), N2a/N2b (4 to 6 v ≥ 7). Five-year observed and relative survival data were obtained for each TN category. Results: SEER colon cancer analyses confirm that patients with T1-2N0 cancers have better survival than T3N0, T3N0 better than T4N0, T1-2N2 better than T3-4N2, and T4bN1 similar to T4N2. Patients with T4a lesions have better survival than T4b by N category. The number of positive nodes affects survival for each T category. Conclusion: This SEER population-based colon cancer analysis is highly consistent with rectal cancer pooled analysis and SEER rectal cancer analyses, supporting the shift of T1-2N2 lesions from IIIC to IIIA/IIIB, shifting T4bN1 from IIIB to IIIC, subdividing T4/N1/N2, and revising substaging of stages II/III. Survival outcomes by TN category for colon and rectal cancer are strikingly similar.