In the past, a standard gastrectomy, including the resection of more than two thirds of stomach and a D2 lymph node dissection, is the major treatment method for EGC and AGC. But, with the development of endoscopic technique, endoscopic resection, including EMR and ESD, has been widely used in the patients of EGC. Recently, researches have showed that in EGC, there was no significant difference in overall survival between the patients underwent radical gastrectomy and endoscopic resection, although the latter had a higher recurrence rate (8)(9). And the complication rate of endoscopic resection is lower than that of radical gastrectomy (8).
For those EGC patients who underwent endoscopic resection, lymph node metastasis has a significant adverse effect on the prognosis. So, endoscopic resection was suggested to be used in the EGC with a low possibility of lymph node metastasis. In our screened data, the lymph node metastasis rate of T1a gastric cancer is 10.1%, while in all T1a gastric cancer patients in SEER database, this rate is 9.7%. Choi (19) reported that the lymph node metastasis rate of T1a gastric cancer in western population is 7.8%, which is relatively close to our data. But Gotoda (20) suggested the lymph node metastasis rate of intramucosal cancers in the Japanese people is 2.2%. This could be because of ethnic differences, but it could also be because of other factors and all residents over 40 years old in Japan will be screened for gastric cancer (21). Therefore, they can always detect gastric cancer at a very early stage, which may be one of the reasons for its low lymph node metastasis rate. However, even after careful examination, it is still possible to misjudge whether there is lymph node metastasis. A method to predict the rate of lymph node metastasis is needed clinically.
Previous studies have shown that for EGC, age, tumor size, tumor location, ulceration, histological type, grade, macroscopic appearance (Such as ulcer, border, color) and depth of invasion are risk factors of lymph node metastasis (22-25). Especially the depth of invasion is the most critical risk factors. Only patients with T1a gastric cancer, whose depth of invasion is limited to the mucosa are suitable for ESD/EMR treatment in Japanese gastric cancer treatment guidelines. Thus, the object of our study were the patients with T1a gastric cancer. In this study, we selected seven factors (Sex, Race, Age, Primary site, Tumor size, Grade and Histologic type) to study their relationship with lymph node metastasis in EGC. After chi-square analysis, we found that for EGC, four factors (Race, Tumor size, Grade and Histologic type) were significantly related to the risk of lymph node metastasis. By logistic regression analysis, Race, Tumor size and Grade were considered to be the independent factors of lymph node metastasis. EGC with diameter>3cm or poor differentiation is prone to lymph node metastasis. In addition, blacks and whites are more likely than others to develop lymph node metastasis. Many studies had focused on the lymph node metastasis rate in EGC and its influencing factors, but there is a lack of a suitable method to predict lymph node metastasis of EGC clinically.
Nomogram has been widely used in the prediction of various clinical events. This is the first time a nomogram was used to predict lymph node metastasis in EGC. In this study, we construct a nomogram to directly predict the possibility of lymph node metastasis of EGC in T1a stage based on these four variables (Race, Tumor size, Grade and Histologic type) and the results of C-index, Calibration curve and ROC curve had revealed its great ability of prediction on lymph node metastasis. With this nomogram, we can calculate the score based on the level of the four variables, and then get the corresponding lymphatic metastasis rate according to the score in clinical practice. For patients with a low risk of lymph node metastasis, endoscopic resection might be a better treatment. In contrast, the patients with a high risk of lymph node metastasis are better candidates for standard gastrectomy or endoscopic resection with laparoscopic lymph node dissection (26).