Better grading systems for evaluating the degree of lymph node invasion in cancer of the thoracic esophagus.

To evaluate the quality of various grading systems for lymph node invasion in cancer of the thoracic esophagus, the surgical results of 142 patients who underwent systematic lymph node dissection with curative intent were analyzed. The survival probability of patients in the same grade was modeled using a Weibull distribution and the parameters were estimated by the maximum likelihood principle. The quality of each grading system was measured by the Akaike Information Criterion (AIC) of the estimated statistical model, by which the smaller the AIC of a grading system, the smaller the loss of information for predicting outcomes. The AIC of the TNM grading of the International Union Against Cancer, the grading of the Japanese Society for Esophageal Diseases, and the grading designed according to the total number of positive lymph nodes became substantially smaller in that order. The AIC of grading systems variously designed on rather simple criteria were examined with the aim of creating a better grading system. It was concluded that a grading system based on the total number of positive nodes and the state of the paratracheal and/or middle mediastinal node groups was better than the other systems examined.