Metastatic lymph node ratio in advanced gastric carcinoma: a better prognostic factor than number of metastatic lymph nodes?

Gastric carcinoma is the most common cancer and the second most common cause of cancer-related death in Korea. Many studies have been reported regarding prognostic factors. Among the category I prognostic factors of gastric carcinoma, lymph node metastasis (nodal status) is considered to be the strongest prognostic factor. According to the current UICC (the International Union Against Cancer)/AJCC (American Joint Committee on Cancer) staging system, nodal status is categorized based on the number of metastatic lymph nodes (pN0, no metastasis; pN1, 1-6 lymph nodes positive; pN2, 7-15 and pN3, >15). Some groups have recently proposed the metastatic lymph node ratio (the ratio between metastatic lymph nodes and total dissected lymph nodes; MLR) as an alternative prognostic factor to supplement the limitations of the conventional N staging system, particularly when a limited number of lymph nodes is obtained. In the present study, we aimed to evaluate which lymph node assessment method, metastatic lymph node number vs. ratio of metastasis, was better to predict survival in comparison with known prognostic factors in advanced gastric carcinoma in Korea. In addition, we tried to determine what level of MLR was a statistically significant factor to get a meaningful separation of survival. Based on our study, we demonstrate that the MLR was a simple and reproducible prognostic factor that supplemented the limitation of the conventional N staging system, and provided more accurate prognostic stratification in advanced gastric cancer. In addition to patients' age, tumor size, and chemotherapy, MLR was a strong prognostic factor in multivariate analysis, although the number of lymph node metastases, was not a strong factor. The MLR demonstrated further survival influence in pN2 stage. Moreover, with the relationship to pT stage, MLR showed better survival information than that of ordinary AJCC pN stage. We also propose that the optimal cut off values for the MLR should be classified into four groups as follows: MLR0, 0; MLR1, >0-0.3; MLR2, >0.3-0.6 and MLR3, >0.6.