Revisiting Dukes' paradigm; some node positive colon cancer patients have better prognosis than some node negative patients

Background The current study tried to evaluate the prognostic value of a modified staging system compared to the American Joint Committee on Cancer (AJCC) staging system for patients with colon cancer. Patients and methods Surveillance, epidemiology and end results (SEER) database (2004-2014) was queried through SEER*Stat program and AJCC 7th stages were constructed. Through recursive partitioning analysis and subsequent decision tree formation, suggested new stages were formulated based on T and N descriptors. Overall survival analyses were performed through Kaplan-Meier analysis. The cancer-specific Cox regression hazard (adjusted for age, gender, sub-site, grade, race and surgery) was calculated and pair wise comparisons of hazard ratios were conducted. Results A total of 159,683 non-metastatic patients with colon cancer were recruited in the analysis. Pair wise hazard ratio comparisons among different AJCC 7th stages were conducted and all comparisons were significant (P < 0.0001). However, it should be noted that the adjusted risk of death among stage IIC patients was higher than stage IIIA and IIIB. Pair wise hazard ratio comparisons among different modified system stages were also conducted and all comparisons were significant (P < 0.0001). The outcomes of survival analysis were the same regardless of the number of examined lymph nodes (< 12 vs. >= 12). Concordance index (using death from colon cancer as the dependent variable) for AJCC 6th staging system was 0.704 (SE 0.002; 95% CI 0.701-0.708); for AJCC 7th staging system was 0.708 (SE 0.002; 95% CI 0.704-0.711); for Dukes staging system was 0.670 (SE 0.002; 95% CI 0.666-0.674); and for modified staging system was 0.712 (SE 0.002; 95% CI 0.709-0.716). Conclusion The proposed modified staging system provided an improved prognostication for colon cancer patients (particularly for stage II/III disease) compared to AJCC staging system. Further external validation of the proposed staging system is needed before adoption into routine practice.