ESR1 and undifferentiated carcinoma of stomach: Although the diagnosis of undifferentiated gastric carcinoma with neuroendocrine differentiation had been suggested from the microscopic observation (a scatter mucosal spread of neoplastic signet ring cells) of biopsy specimens, and on the basis of the poor clinical history, the diffuse and strong positivity for ER, PR, CK7 and GDFP15 as well as the negativity for CA 19.9 and CK20 suggested that the breast was the primary site of the neoplasm.