We retrospectively analyzed whether it would be beneficial to determine the lymph node ratio rather than the N category of the TNM system in prognosis of colon cancer. Therefore, we picked 142 stage III colon cancer patients from a cohort of 939 colorectal cancer patients who were operated on over a 10-year period. In comparison to other reports , the fraction, Stage III patients in comparison to all (I to IV) patients) is rather small but the number of examined lymph nodes is rather high [8, 10] as is the percentage of patients receiving adjuvant chemotherapy .
For easier comparison of N stages to lymph node ratio, we decided to calculate two groups of lymph node ratios. By doing so, there is no superiority in predicting disease-free and overall survival of the lymph node ratio to the N category of the TNM system. Other authors split patient cohorts by random or percentiles rather than calculating groups [6, 7, 9, 11]. By using more groups, the lymph node ratio gains in precision of prognosis [6, 7, 11], but if more subgroups were established in the N category, precision would presumably rise there as well. So, in our opinion, the only possibility for comparing the two approaches is to use the same number of groups.
To exclude the bias of neoadjuvant treated patients, we decided not to include rectal cancer patients in the analysis. In rectal cancer patients, the number of pathologically diagnosed lymph nodes is frequently lowered after neoadjuvant treatment in comparison to patients not treated with neoadjuvants . Therefore, all rectal cancer patients were excluded from this analysis. Other authors used a stage I to IV colorectal cancer cohort over many years to show the advantage of the lymph node ratio . The disadvantage of this particular approach is that there are many patients included who do not have lymph node metastasis at all, have distant metastasis synchronously and that patients were operated over a long time period. Within this period, surgical techniques might have changed substantially, and therefore, it might be difficult to compare patients’ courses of the disease.