Hui Y, et al. - An inspection was conducted of the expression patterns of several common immunohistochemical markers in tumors with signet-ring morphology in order to differentiate between breast carcinoma with Signet-ring features from gastrointestinal Signet-ring carcinoma. Similar discriminatory characteristics were demonstrated by these markers when comparing lobular and gastric signet ring carcinomas. Successful discrimination between breast and gastric primary sites was achieved in 15 out of 16 cases. Estrogen receptor (ER) and GATA-3 were determine to be most supportive of mammary origin. Both presented as an effective panel for distinguishing primary breast from primary gastrointestinal signet-ring tumors when combined with CK20 and CDX2 immunohistochemistry.