80 Kwon SJ the lymph nodes with no respect to the number of lymph nodes dissected, even though the number of dissected lymph nodes was no greater than 16, could be classified as N0 group”, revisions were made in that the dissection of more than 16 lymph nodes would not be mandatory (the classification is pNo if the examined lymph nodes are negative but the number ordinarily resected is not met.). Previous studies reported contradictory results in that correct disease staging could become difficult due to stage migration in cases in whom the number of dissected lymph nodes was insufficient.(8,9) Based on these revisions, stage migration could occur in many cases. According to Hundahl et al.,(10) based on the disease staging performed for cases of gastric cancer surgery in North America, the proportion of those with more than 15 lymph nodes dissected was at most 18%. One study examined the validity of staging for cases of esophagogastric (EG) junction cancer through a comparison between the adequate staging group where more than 15 lymph nodes were dissected and an inadequate staging group where less than 15 lymph nodes had been dissected.(11) They reported that the TNM staging could be performed accurately only in cases in whom more than 15 lymph nodes had been dissected. In particular, this would make it possible to accurately predict the prognosis of patients with progressive gastric cancer. According to INT-0116(12) and MAGIC Trial,(13) both of which were large-scale, randomized clinical studies conducted in America and Europe, the proportion of cases in whom a more extensive D2 lymph node dissection was performed was 10% and 41.4%, respectively. In addition, the proportion of cases in whom the D0 lymph node dissection, i.e., a less D1 lymph node dissection, was performed on 54% and 15.1%, respectively. According to ACTS-GC, a prospective, in randomized clinical study recently conducted in Japan, 99.8% of cases had a D2 lymph node dissection. This is contradictory to the above reports. Of the total cases of gastric cancer surgery, which was performed at large-volume centers in Korea and the USA, the proportion of those in which less than 15 lymph nodes were dissected was 3% and 22%, respectively. A comparison of the survival rate of patients between the two hospitals during the same disease duration revealed the survival rates of patients with stage I/II/III to be significantly higher in Korea compared to USA.(14) One of the major causes of these results might be stage migration resulting from an insufficient lymph node dissection. In cases in whom the dissection of more than 15 lymph nodes is an essential condition for the TNM staging, it might be impossible to determine the TNM stage in many patients from the USA and Europe. The current guidelines might have been loosened considering this in the seventh edition. In a future TNM staging system, the untoward effects called ‘a lower standardization’ can be prevented provided it is specified as the essential condition for TNM staging that more than 16 lymph nodes should be dissected. The Proportion of Lymph Nodes with Metastasis In the UICC and AJCC TNM Classification, the cuff-off point of the scope of lymph nodes with a metastasis has been revised continuously. To date, its gold standard has not been identified. Given this background, the proportion of lymph nodes with a metastasis relative to the number of dissected lymph nodes was divided into several segments. Some suggest that it should be used as a tool for assessing the degree of lymph node metastasis.(15- 17) In addition, the proportion of lymph nodes with a metastasis exceeds the ability to predict the prognosis based on the pre- existing TNM Classification, even in cases of breast cancer, colon cancer and rectal cancer.(18-20) As reported by Lemmens et al.,(21) the proportion of lymph nodes with a metastasis was first proposed as a measure to overcome the limitations of a lymph node dissection. The methods for screening the lymph nodes with a metastasis were once assessed as the best tool for predicting the prognosis. This might not be superior to the classification based on the N category due to reasons such as the limitation in the number of dissected lymph nodes, the insufficiency in a consensus on the segment interval and the insufficiency in a consensus on the scope of lymph node metastasis. In cases for which surgery was performed with a smaller number of dissected lymph nodes in the USA and Europe, it might also be a good method that can be used alternatively to the pre-existing TNM classification. Constituents Forming the TNM Stage IV In the sixth edition, the TNM stage IV included M0 and M1, which showed a significant difference in the survival rate. Considering this, several authors reported that staging should be done in such a manner that stage IV should be differentiated into stages IVa and IVb according to M0 or M1.(22-25) Given this background, in the seventh edition, only distant metastasis-positive cases (M1) were classified as stage IV. Although there are many lymph nodes with a metastasis or the degree of invasion to the gastric wall is as high as possible, the corresponding cases were classified as stages other than stage IV. Therefore, differentiation