Is the lymph node ratio superior to the Union for International Cancer Control (UICC) TNM system in prognosis of colon cancer?

Background: Decision making for adjuvant chemotherapy in stage III colon cancer is based on the TNM system. It is well known that prognosis worsens with higher pN classification, and several recent studies propose superiority of the lymph node ratio (ln ratio) to the TNM system. Therefore, we compared the prognosis of ln ratio to TNM system in our stage III colon cancer patients. Methods: A total of 939 patients underwent radical surgery for colorectal cancer between January 2000 and December 2009. From this pool of patients, 142 colon cancer stage III patients were identified and taken for this analysis. Using martingale residuals, this cohort could be separated into a group with a low ln ratio and one with a high ln ratio. These groups were compared to pN1 and pN2 of the TNM system. Results: For ln ratio, the cutoff was calculated at 0.2. There was a good prognosis of disease-free and cancer-related survival for the N-category of the TNM system as well as for the lymph node ratio. There was no statistical difference between using the N-category of the TNM system and the ln ratio. Conclusions: There might not be a benefit in using the lymph node ratio rather than the N category of the TNM system as long as the number of subgroups is not increased. In our consideration, there is no need to change the N categorization of the TNM system to the ln ratio.