AJCC Cancer Staging Manual 7th edition criteria for colon cancer: do the complex modifications improve prognostic assessment?

Abstract

Background: The 7th edition of the AJCC Cancer Staging Manual (AJCC-7) includes substantial changes for colon cancer (CC), which are particularly complex in patients with stage II and III disease. We used a national cancer database to determine if these changes improved prediction of survival.

Study design: The database of the Surveillance, Epidemiology and End Results Program was queried to identify patients with pathologically confirmed stage I to III CC diagnosed between 1988 and 2008. Colon cancer was staged by the 6(th) edition of the AJCC Cancer Staging Manual (AJCC-6) and then restaged by AJCC-7. Five-year disease-specific survival and overall survival were compared.

Results: After all exclusion criteria were applied, AJCC-6 and AJCC-7 staging was possible in 157,588 patients (68.9%). Bowker's test of symmetry showed that the number of patients per substage was different for AJCC-6 and AJCC-7 (p < 0.001). The Akaike information criteria comparison showed superior fit with the AJCC-7 model (p < 0.001). However, although AJCC-7 staging yielded a progressive decrease in disease-specific survival and overall survival of patients with stage IIA (86.3% and 72.4%, respectively), IIB (79.4% and 63.2%, respectively), and IIC (64.9% and 54.6%, respectively) CC, disease-specific survival and overall survival of patients with stage IIIA disease increased (89% and 79%, respectively). Subset analysis of patients with >12 lymph nodes examined did not affect this observation.

Conclusions: The AJCC-7 staging of CC does not address all survival discrepancies, regardless of the number of lymph nodes examined. Consideration of other prognostic factors is critical for decisions about therapy, particularly for patients with stage II CC.

Keywords: AIC; AJCC; AJCC Cancer Staging Manual, 6(th) edition; AJCC Cancer Staging Manual, 7(th) edition; AJCC-6; AJCC-7; Akaike information criterion; American Joint Committee on Cancer; CC; DSS; LN; OS; SEER; Surveillance, Epidemiology and End Results; colon cancer; disease-specific survival; lymph node; overall survival.

Figure 1

Flow diagram of patient selection from the 258,552 patients with colon cancer to establish patients with stages I-III who had surgical resection with curative intent within the SEER database from 1988-2008.

Figure 2

Five-year disease-specific survival (DSS) and overall survival (OS) for the 157,588 patients whose colon cancer was staged based on AJCC-6 (orange) and AJCC-7 (black) criteria. (A) DSS for stages I-III. (B) DSS for all substages. (C) OS for stages I-III (D) OS for all substages.

Figure 3

Five-year survival based on number of lymph nodes (LNs) examined: 1-11 LNs (red) and ≥ 12 LNs (black). (A) disease-specific survival, and (B) overall survival.

Figure 4

Five-year disease-specific survival (DSS) and overall survival (OS) for all patients based on substaging and number of LNs examined. AJCC-6 (< 12 lymph nodes [LNs] yellow, 12+ LNs red) and AJCC-7 (<12 LNs green, 12+ LNs blue) criteria. (A) DSS for Stages I-III. (B) OS for Stages I-III.