Signet Ring Carcinoma (SRC) is considered to be a variant of infiltrating lobular carcinoma and consists of tumor cells with intracellular mucin accumulation resulting in signet ring appearance. This tumor must be separated from mucinous (colloid) carcinoma in which the mucin is predominantly extracellular. Exceptions do occur, however, in both directions. Majority of the tumor cells should have signet ring morphology for a tumor to be labeled as signet ring carcinoma. In this image, the lower part shows the classical pattern of lobular carcinoma transitioning to signet ring cell pattern in the upper half. Higher magnification of the previous image.