For the early gastric cancers, an endoscopic submucosal dissection is the first choice treatment in Japan, but the criteria of the additional surgery including lymph node dissection after the ESD are still controversial. Our series of immunohistochemistry studies for mucin expression in various human neoplasms have demonstrated that the expression of the MUC1 mucin is related with invasive proliferation of the tumors and poor outcome of the patients, whereas the expression of the MUC2 mucin is related with the non-invasive proliferation of the tumors and a favorable outcome for the patients. Our previous study showed that MUC1 expression in gastric cancers is a poor prognostic factor. MUC4 was first reported as tracheobronchial mucin and is a membrane-associated mucin. In our study series, the expression of MUC4 in intrahepatic cholangiocarcinoma, pancreatic ductal adenocarcinoma, extrahepatic bile duct carcinoma, lung adenocarcinoma, and oral squamous cell Regorafenib carcinoma was an independent factor for poor prognosis and is a useful marker to predict the outcome of the patients. Unfortunatly, there are few studies of the MUC4 expression profile in human gastric cancer. In the present study, we examined the expression profiles of MUC4 as well as MUC1 in early gastric cancer tissues, and found that MUC4 and MUC1 expression in the early gastric cancers would become poor prognostic factors by lymph vessel invasion, blood vessel invasion and lymph node metastasis. As anti-MUC4 monoclonal antibodies, 8G7 and 1G8, are known to detect different sites of MUC4 molecule. The MAb 1G8 is raised against the rat sequence, and recognizes an epitope on the rat ASGP-2 subunit, which corresponds to the human MUC4b subunit, and shows a cross reactivity with human samples. Thus, a special attention was paid to the comparison of two anti-MUC4 MAbs by Western blotting and IHC of two gastric cancer cell lines, before the IHC study of human gastric cancer tissues. Moreover, since there is controversy regarding the prognostic significance of these antiMUC4 MAbs, a literature review of MUC4 expression in various cancers was also performed. Recently, we have reported that the expression of MUC4 is an independent poor prognostic factor of pancreatobiliary adenocarcinomas as well as lung adenocarcinoma and oral squamous cell carcinoma. MUC1 has also been reported to be a poor prognostic factor in various human neoplasms. Our previous study in gastric cancers, including both early cancers and advanced cancers demonstrated that MUC1 is a useful prognostic factor for poor outcome in the patients. In the present study, the relationship between mucin expression and the patient’s outcome cannot be evaluated, because the gastric cancers are in the early stage at pT1b2 and most of the patients have had a favorable outcome. Nevertheless, the following results were obtained: The MUC4/8G7, MUC4/1G8 and MUC1/DF3 expressions were related with lymphatic invasion. The MUC4/ 1G8 expression was related with lymph node metastasis. The MU1/DF3 expression was related with venous invasion. In Japan, ESD is the first choice treatment for early gastric cancers. Examination of MUC4 as well as MUC1 in the ESD specimens may clarify whether the additional surgery, including lymph node dissection or frequent follow-up for the metastasis are necessary. Our previous studies demonstrated that there was no siginificant correlation between MUC4 expression and MUC1 expression. Also in the present study of the gastric cancers in the early stage, there was no siginificant correlation between expression of MUC4 and MUC1. Both MUC4 and MUC1 expression in the gastric cancers may be related with the poor prognostic factors, such as lymphatic invasion, venous invasion and lymph node metastasis.