Abstract:The estrogen receptor was studied in a total of 42 cases of gastric carcinoma which included 14 cases of the penetrating type of early gastric carcinoma (PEN), 14 cases of the common type of early gastric carcinomas (EA) and 14 cases of the advanced gastric carcinomas (AD). An immunohistochemical study using the anti‐ER‐D5 antibody revealed that the detection of estrogen receptor‐positive tumor cells was significantly higher in the PEN group and in the AD group than in the EA group. Moreover, the incidence of estrogen receptor immunoreactivity in infiltrative and scirrhous PENs was significantly higher than that in non‐infiltrative and non‐scirrhous PENs. These results suggests that the estrogen receptor may play an important role in infiltrative proliferation and scirrhous growth in the PENs. Furthermore, the results indicated that ER immunostaining procedures applied to endoscopic biopsy specimens could be useful for the endoscopic diagnosis of PEN‐type early gas